Cycling: A particularly beneficial exercise for the health of diabetics

Cycling: A particularly beneficial exercise for the health of diabetics

OVERVIEW

  • Exercise and physical activity bring many benefits for people with type 2 diabetes.
  • Among a large cohort of 110,944 people from 10 European countries, 7,459 people had type 2 diabetes, 37% of whom were cyclists.
  • After a 5-year follow-up, the researchers found that fewer premature deaths and deaths from cardiovascular disease occurred proportionately among cyclists than among non-cyclists.
  • Participants who started cycling after the start of the study also saw their risk of death significantly reduced, showing that it is never too late to get on that bike and reap the health benefits.

Diabetes increases the risk of developing cardiovascular disease and of dying prematurely from cardiovascular causes and from any cause. Regular physical activity and exercise reduce risk factors for cardiovascular disease in people with diabetes.

Benefits of aerobic exercise
In diabetics, aerobic training (brisk walking, running, cycling, etc.) increases insulin sensitivity, mitochondrial density (production of energy in cells), vascular reactivity, immune and pulmonary functions, and cardiac output. In addition, regular training lowers the level of glycated hemoglobin and triglycerides in the blood as well as blood pressure.

Benefits of resistance exercise
Diabetes is a risk factor for having poor muscle tone, and it can lead to a faster decline in muscle strength and function. A few mechanisms have been proposed to explain this phenomenon in diabetics, including: 1) endothelial dysfunction secondary to high blood glucose levels which cause vasoconstriction of the vessels that nourish muscles and 2) disruption of skeletal muscle energy metabolism through a dysfunction of the mitochondria (elements of the cell that produces its energy).

Benefits of resistance training (weightlifting, use of a resistance band, etc.) in the general population include improvements in muscle mass and strength, fitness, bone mineral density, insulin sensitivity, blood pressure, lipid profile, and cardiovascular health. For diabetics (type 2), resistance training improves blood sugar control, insulin resistance, blood pressure, muscle strength, lean body mass vs. fat mass.

Benefits of other types of exercise
People with diabetes are particularly affected by the loss of joint mobility, a condition caused in part by the build-up of end products of glycation that occurs during normal aging, but is accelerated by hyperglycemia. People with diabetes can therefore benefit from stretching exercises that allow them to increase the flexibility and mobility of their joints.

Cycling and mortality risk in diabetics
Is there one physical activity that is more beneficial than others to improve the health of people with diabetes and reduce the risk of premature death? A prospective study of 7,459 adults with diabetes, with an average age of 55.9 years, assessed whether there is an association between time spent cycling and cardiovascular mortality or from any cause. Participants, who had been diabetic for an average of 7.7 years at the start of the study, completed detailed questionnaires upon enrollment and 5 years later. Compared with participants who did not cycle at all (0 minutes/week), those who did had a lower risk of death from any cause, from 22% (1 to 59 min/week) to 32% (150 to 299 min/week). Reductions of the same order of magnitude (21 to 43%) were observed for cardiovascular mortality. These reductions in mortality risk were independent of other physical activities reported by participants and other confounding factors (level of education, smoking, adherence to the Mediterranean diet, total energy intake, occupational physical activity).

Another question the study researchers wanted to answer was whether stopping or starting to cycle during the 5-year follow-up had an effect on the risk of death of participants with diabetes. The results indicate that participants who cycled after the start of the study had a significantly lower risk of cardiovascular and all-cause mortality compared to non-cyclists. Participants who instead stopped cycling after starting the study had a similar risk of premature death to that of non-cyclists. It is therefore never too late to start cycling and reap significant health benefits, provided that this exercise is practised regularly, without interruption.

Other researchers found it surprising that the association between cycling and a reduction in the risk of mortality is independent of other physical activities. They point out that there is a relationship between the amount of physical activity and the reduction in mortality (4% reduction in risk per 15 minutes of additional physical activity per day) for healthy people and those with cardiovascular disease according to published data. They questioned whether a bias comparable to that of the “healthy worker effect” is not at issue here. This bias could be caused in this case by the fact that diabetics who cycle are healthier than those who do not, resulting in lower premature mortality. In their response to this criticism, the study authors say they agree that cyclists might be healthier than non-cyclists, but they say they did all they could to minimize this potential bias by adjusting the results to take into account risk factors for premature mortality, including diet, physical activity other than cycling, incidence of myocardial infarction and cancer, and excluding smokers, former smokers and individuals who play sports. The authors conclude that they are convinced that cycling can directly contribute to reducing premature mortality, but that in this type of study it is always possible that there are known or unknown confounding factors.

An earlier study had previously reported that cycling had advantages over other physical activities. This study was carried out about 20 years ago with 30,640 participants in the Copenhagen region of Denmark. In the 14.5 years of follow-up, people who cycled to work had a 40% lower risk of dying prematurely than non-cyclist participants, after accounting for possible confounding factors, including the amount of physical activity during leisure time.

Cycling requires being fit, having a good sense of balance, and having the financial means to buy a bicycle. In addition, cycling must be done in a safe environment, which is increasingly possible with the addition of cycle paths in recent years. In Quebec, cycling cannot be practised safely during the winter, namely for more than 4 months, but it is fortunately possible to ride a stationary bike at home or in training centres. In recent years, there has been real enthusiasm for cycling, including the electric bicycle, which allows older or less fit people to climb slopes without much effort. Let’s hope that this enthusiasm continues so that more people who are healthy or have a chronic illness can benefit from the health benefits of this extraordinary physical activity.

Gradual return to physical activity after recovering from COVID-19

Gradual return to physical activity after recovering from COVID-19

OVERVIEW

  • People with persistent symptoms or who have had a severe form of COVID-19 or who may have a history of cardiopathy should consult a doctor before resuming physical activity.
  • People who have had a mild form of COVID-19 and want to resume physical activity should do so very gradually.
  • Do not resume exercise until at least seven days without symptoms and start with at least two weeks of minimal exercise.
  • Use daily self-monitoring to track your progress and determine when to seek additional medical help if needed.

Here we provide a summary of guidelines and advice from public health organizations for returning to exercise after COVID-19 (see hereherehere and here).

After a mild form of COVID-19, some people have a prolonged recovery, especially when trying to resume exercise. In addition, many affected people may have long-term complications from COVID-19, including chronic COVID syndrome (post-COVID syndrome or long COVID), cardiopulmonary disease, and, in some people, psychological sequelae (1234). This article presents a pragmatic approach to help people safely return to physical activity after symptomatic SARS-CoV-2 infection, focusing on those who have lost their physical condition or have had a prolonged period of inactivity but who do not have chronic COVID syndrome.

The health benefits of physical activity, for cardiovascular as well as mental health, are well established (56). Conversely, the harms of physical inactivity make it a major risk factor for noncommunicable diseases around the world, as are smoking and obesity (7). Before the COVID-19 pandemic, the majority of adult Canadians (82.5%) did not meet physical activity guidelines (at least 150 minutes of moderate-intensity physical activity per week at a rate of at least 10 minutes per session) and were sedentary for most of the day (9.6 hours) (8). There has been a further decline in physical activity since the start of the pandemic among people with chronic conditions like obesity and hypertension (9), conditions that are associated with severe forms of COVID-19 (10). Brief advice can help people engage in physical activity, with the associated positive health effects, and help those recovering from illness to return to previous levels of physical activity or beyond (11). Some people may not know how and when to resume physical activity after COVID-19, and if it is safe. Some may have tried returning to their baseline exercise and found that they were unable to do so.

You should consult a doctor before exercising after having COVID-19 when:

  • The illness required treatment in the hospital.
  • Myocarditis has been diagnosed.
  • You experienced heart symptoms during the illness (chest pain, palpitations, severe shortness of breath or syncope).
  • You experience persistent symptoms (respiratory, gastrointestinal, rheumatic or other).

If you had no complications during the illness and have had no symptoms for 7 days, you can gradually resume physical activity (Figure 1):

Resuming in four phases (minimum of 7 days for each phase):

Phase 1: Very low intensity physical activity, such as flexibility and breathing exercises.

Phase 2: Low-intensity physical activity such as slow walking, light yoga, light housework and gardening, gradually increasing the duration to 10–15 minutes per day, when the exercise is well tolerated.

At both phases 1 and 2, the person should be able to hold a normal conversation without difficulty while doing the exercises.

Phase 3: Aerobic and strength exercises of moderate intensity, such as brisk walking, jogging, swimming, cycling, going up and down stairs. You shouldn’t feel like the exercise is “hard”. It is recommended to do two 5-minute intervals of exercise separated by a recovery block. People should add one interval per day if exercise is well tolerated.

Phase 4: Aerobic and strength exercises of moderate intensity with control of coordination and functioning skills, such as running with changes of direction, side steps, but without it feeling too difficult. Two days of training followed by a day of recovery.

Phase 5: Return to regular exercise (pre-COVID).

 

Figure 1. Suggested return to physical activity after COVID-19. Adapted from Salman et al., BMJ, 2021.

 

It is proposed to devote a minimum of 7 days to each phase to avoid sudden increases in training load. However, people should stay at the stage they feel comfortable with for as long as necessary. Watch for any inability to recover 1 hour after exercise and the next day, for abnormal shortness of breath, abnormal heart rate, excessive fatigue or lethargy, and markers of poor mental health. If this happens or if you are not progressing as planned, you should return to a previous phase and seek medical attention if in doubt. Keeping a journal of exercise progress, as well as the intensity of exertion, any changes in mood and, for those who are used to measuring it, objective fitness data such as heart rate, can be useful in tracking progress.

Effects of cold on cardiovascular health

Effects of cold on cardiovascular health

OVERVIEW

  • Exposure to cold causes a contraction of blood vessels as well as an increase in blood pressure, heart rate, and the work of the heart muscle.
  • The combination of cold and exercise further increases stress on the cardiovascular system.
  • Cold temperatures are associated with increased cardiac symptoms (angina, arrhythmias) and an increased incidence of myocardial infarction and sudden cardiac death.
  • Patients with coronary artery disease should limit exposure to cold and dress warmly and cover their face when exercising.

Can the sometimes biting cold of our winters affect our overall health and our cardiovascular health in particular? For an exhaustive review of the literature on the effects of cold on health in general, see the summary report (in French only) recently published by the Institut national de santé publique du Québec (INSPQ). In this article, we will focus on the main effects of cold on the cardiovascular system and more specifically on the health of people with cardiovascular disease.

Brief and prolonged exposure to cold both affect the cardiovascular system, and exercise in cold weather further increases stress on the heart and arteries. Numerous epidemiological studies have shown that cardiovascular disease and mortality increase when the ambient temperature is cold and during cold spells. The winter season is associated with a greater number of cardiac symptoms (angina, arrhythmias) and cardiovascular events such as hypertensive crisis, deep venous thrombosis, pulmonary embolism, aortic ruptures and dissections, stroke, intracerebral hemorrhage, heart failure, atrial fibrillation, ventricular arrhythmia, angina pectoris, acute myocardial infarction, and sudden cardiac death.

Mortality from cold
Globally, more temperature-related deaths were caused by cold (7.29%) than heat (0.42%). For Canada, 4.46% of deaths were attributable to cold (2.54% for Montreal), and 0.54% to heat (0.68% for Montreal).

Intuition may lead us to believe that it is during periods of extreme cold that more adverse health effects occur, but the reality is quite different. According to a study that analyzed 74,225,200 deaths that occurred between 1985 and 2012 in 13 large countries on 5 continents, extreme temperatures (cold or hot) accounted for only 0.86% of all deaths, while the majority of cold-related deaths occurred at moderately cold temperatures (6.66%).

Acute effects of cold on the cardiovascular system of healthy people

Blood pressure. The drop in skin temperature upon exposure to cold is detected by skin thermoreceptors that stimulate the sympathetic nervous system and induce a vasoconstriction reflex (decrease in the diameter of the blood vessels). This peripheral vasoconstriction prevents heat loss from the surface of the body and has the effect of increasing systolic (5–30 mmHg) and diastolic (5–15 mmHg) blood pressure.

Heart rate. It is not greatly affected by exposure of the body to cold air, but it increases rapidly when, for example, the hand is dipped in ice water (“cold test” used to make certain diagnoses, such as Raynaud’s disease) or when very cold air is inhaled. Cold air usually causes a slight increase in heart rate in the range of 5 to 10 beats per minute.

Risk of atheromatous plaque rupture?
Post-mortem studies have shown that rupture of atheroma plaques (deposits of lipids on the lining of the arteries) is the immediate cause of over 75% of acute myocardial infarctions. Could cold stress promote the rupture of atheromatous plaques? In a laboratory study, mice exposed to cold in a cold room (4°C) for 8 weeks saw their blood LDL cholesterol level and the number of plaques increase compared to mice in the control group (room at 30°C). Furthermore, it is known that exposure to cold induces aggregation of platelets in vitro and increases coagulation factors in vivo in patients during colder days (< 20°C) compared to warmer days (> 20°C). Combined, these cold effects could help promote plaque rupture, but to date no study has been able to demonstrate this.

Risk of cardiac arrhythmias
Arrhythmias are a common cause of sudden cardiac death. Even in healthy volunteers, the simple act of dipping a hand in cold water while holding the breath can cause cardiac arrhythmias (nodal and supraventricular tachycardias). Could cold promote sudden death in people at risk for or with heart disease? Since arrhythmias cannot be detected post-mortem, it is very difficult to prove such a hypothesis. If it turns out that exposure to cold air can promote arrhythmias, people with coronary artery disease may be vulnerable to the cold since the arrhythmia would amplify the oxygenated blood deficit that reaches the heart muscle.

Effects of cold combined with exercise
Both cold and exercise individually increase the heart’s demand for oxygen, and the combination of the two stresses has an additive effect on this demand (see these two review articles, here and here). Exercising in the cold therefore results in an increase in systolic and diastolic blood pressure as well as in the “double product” (heart rate x blood pressure), a marker of cardiac work. The increased demand for oxygen by the heart muscle caused by cold weather and exercise increases blood flow to the coronary arteries that supply the heart. The rate of coronary blood flow increases in response to cold and exercise combined compared to exercise alone, but this increase is mitigated, especially in older people. Therefore, it appears that cold causes a relative lag between the oxygen demand from the myocardium and the oxygenated blood supply during exercise.

In a study carried out by our research team, we exposed 24 coronary patients with stable angina to various experimental conditions in a cold room at – 8°C, specifically a stress test with electrocardiogram (ECG) in cold without antianginal medication and an ECG at + 20°C. We then repeated these two ECGs after taking one drug (propranolol) that slows the heart rate, and then another drug (diltiazem) that causes dilation of the coronary arteries. The results showed that the cold caused mild to moderate ischemia (lack of blood supply) to the myocardium in only 1/3 of the patients. When ECG was done with medication, this effect was completely reversed. The two drugs have been shown to be equally effective in reversing this ischemia. The conclusion: cold had only a modest effect in 1/3 of patients and antianginal drugs are as effective in cold (- 8°C) as at + 20°C.

In another study in the same type of patients, we compared the effects of an ECG at – 20°C with an ECG at + 20°C. The results showed that at this very cold temperature, all patients presented with angina and earlier ischemia.

Hypertension
The prevalence of hypertension is higher in cold regions or during winter. Cold winters increase the severity of hypertension and the risk of cardiovascular events such as myocardial infarction and stroke in people with hypertension.

Heart failure
The heart of patients with heart failure is not able to pump enough blood to maintain the blood flow necessary to meet the body’s needs. Only a few studies have looked at the effects of cold on heart failure. Patients with heart failure do not have much leeway when the heart’s workload increases in cold weather or when they need to exert sustained physical effort. Cold combined with exercise further decreases the performance of people with heart failure. For example, in a study we conducted at the Montreal Heart Institute, cold reduced exercise time by 21% in people with heart failure. In the same study, the use of beta-blocker class antihypertensive drugs (metoprolol or carvedilol) significantly increased exercise time and reduced the impact of cold exposure on the functional capacity of patients. Another of our studies indicates that treatment with an antihypertensive drug from the class of angiotensin converting enzyme inhibitors, lisinopril, also mitigates the impact of cold on the ability to exercise in patients with heart failure.

Cold, exercise and coronary heart disease
It is rather unlikely that the cold alone could cause an increase in the work of the heart muscle large enough to cause a heart attack. Cold stress increases the work of the heart muscle and therefore the blood supply to the heart in healthy people, but in coronary patients there is usually a reduction in blood flow to the coronary arteries. The combination of cold and exercise puts coronary patients at risk of cardiac ischemia (lack of oxygen to the heart) much earlier in their workout than in warm or temperate weather. For this reason, people with coronary artery disease should limit exposure to cold and wear clothes that keep them warm and cover their face (significant heat loss in this part of the body) when working out outdoors in cold weather. In addition, the exercise tolerance of people with coronary heart disease will be reduced in cold weather. It is strongly recommended that coronary heart patients do indoor warm-up exercises before going out to exercise outdoors in cold weather.

Standing up is still doing a little exercise!

Standing up is still doing a little exercise!

OVERVIEW

  • Sedentary lifestyle is associated with a significant increase in the risk of cardiovascular disease, type 2 diabetes, certain types of cancer and an increased risk of dying prematurely.
  • A study of seniors (65 years and older) reported that simply standing for more than an hour a day, without necessarily exercising, is enough to significantly reduce this risk of premature death.

According to recent estimates from the World Health Organization, physical inactivity is directly responsible for around 10% of premature deaths worldwide, an impact similar to those of smoking and obesity. Canada is no exception to this trend, with barely 15% of the population doing the recommended minimum of 150 minutes of physical activity per week and only 5% doing so on a regular basis, i.e. being active for at least 30 minutes a day, five days a week. This sedentary lifestyle is particularly pronounced among older people (60 and over), with barely 10% of this age group being sufficiently active. As a result, it is estimated that the elderly spend on average more than 60% (10 hours and more) of their waking period in sedentary activities, totally devoid of physical activity (Figure 1).

Figure 1. Proportion of waking time spent in sedentary activities by age group. From Matthews et al. (2008).

This is far too much, as numerous studies have clearly shown that high levels of physical inactivity are associated with a significant increase in the risk of cardiovascular disease, type 2 diabetes, certain types of cancer and an increased risk of dying prematurely. There is no doubt that sitting or lying down doing nothing for too long is very bad for health and that itis absolutely necessary to break this bad habit to improve the health of the population.

Standing up is already better
Obviously, the best option to counter the harmful effects of a sedentary lifestyle is to be more physically active. For example, a recent study reports that around 30 minutes of moderate to vigorous physical activity per day (such as brisk walking) seems sufficient to completely cancel out the negative impact of a sedentary lifestyle on the risk of premature mortality.

A study of older people suggests that much lower levels of physical activity may also have positive health effects. In this study, nearly 6,000 American women, ages 63 to 97, wore a research accelerometer for seven days to get accurate measurements of time spent sitting, standing, or moving. During a follow-up period of 5 years on average, the researchers observed that the simple fact of spending more time in a standing position, without doing any other exercise, was enough to significantly decrease the risk of premature death. Compared to the most sedentary women (less than 45 min standing per day), participants who spent the most time standing had a 37% lower risk of death (Figure 2A). These positive effects of standing were even stronger when participants stood and moved at the same time (50% reduction in mortality) (Figure 2B).


Figure 2. Effect of standing (A) or standing with movement (B) on the risk of premature mortality. The values represent the comparison of the mortality rate between the most sedentary people (Q1) and those who are more active (Q4). From Jain et al. (2020).

These results are interesting because many elderly people develop several chronic diseases during aging that weaken them and prevent them from participating in moderate to vigorous physical activities. According to the study, however, these people can improve their health simply by switching from sitting to standing as often as possible.

The transition from sitting to standing requires activating the muscles of the legs and abdominals to lift the body and keep it in balance. These efforts immediately increase blood pressure, heart rate and vascular tone, and the required energy expenditure improves blood vessel function and lipid and carbohydrate metabolism. Although these physiological adaptations are obviously not of the same order as during higher intensity exercise, the results of the study clearly show that they have a positive effect on health and that standing, even without moving, is far better than sitting or lying down for long periods of time.

In short, these results confirm that a sedentary lifestyle is an abnormal behaviour, completely ill adapted to human physiology, and that one should avoid sitting and being inactive for too long as much as possible, regardless of the type of activity performed. And this is true for all ages, young and old alike.

Can exercise protect against respiratory infections?

Can exercise protect against respiratory infections?

OVERVIEW

  • Participants in more than 14 studies were randomly separated into two groups: one group who did not exercise and one who exercised regularly and under supervision.
  • Exercise did not reduce the incidence of acute respiratory infections.
  • Exercise appears to reduce the severity of symptoms associated with episodes of acute respiratory infections.
  • According to several other studies, exercise can improve the immune response to viruses, bacteria and other antigens. Regular physical activity and frequent exercise may reduce or delay the aging of the immune system.

COVID-19 caused by infection with the SARS-CoV-2 virus particularly affects people who have certain risk factors (advanced age, male) or a comorbidity such as chronic respiratory disease, obesity, cardiovascular disease, diabetes, hypertension and cancer (see this article). A healthy lifestyle, including eating well, not smoking, consuming alcohol in moderation, and exercising regularly, is the best way to prevent many diseases such as diabetes, cancer and cardiovascular disease. Also, certain conditions are associated with a decrease in immune activity, for example, stress, diabetes and the deficiency of certain dietary compounds like vitamin D and zinc. By its action on these conditions, exercise is likely to influence our resistance to infections.

Can exercise prevent acute respiratory infections, including COVID-19? Researchers at the Cochrane Library recently updated a systematic review of the effect of exercise on the occurrence, severity and duration of acute respiratory infections.  The systematic review included 14 studies of 1377 healthy individuals aged 18 to 85 who were followed for a median period of 12 weeks. The participants were randomly separated into two groups: one who did not exercise and one who exercised regularly. In most cases, the exercise was supervised and was performed at least three times per week. The exercise sessions lasted 30 to 45 minutes and consisted of moderate intensity exercise such as walking, cycling, treadmill or a combination of these exercises. Exercise did not have a significant effect on biochemical parameters, quality of life or number of injuries.

Exercise did not decrease the number of acute respiratory infections (ARI) episodes, nor the proportion of participants who had at least one episode of ARI during the study, or the number of days with symptoms during each of these episodes. On the other hand, exercise was associated with a decrease in symptom severity in two studies and in the number of days with symptoms during the total study duration (4 studies). The study authors indicate that certainty about the data is low and that data from ongoing or future studies may impact their conclusions.

Exercise and the immune system
The immune system is very responsive to exercise, depending on both the duration and the intensity of effort (see this review article). Exercise causes multiple micro-injuries to the muscles, triggering a local and systemic inflammation reaction. During a moderate to high intensity exercise session lasting less than 60 minutes, the number of leukocytes (white blood cells) and several cytokines (proteins produced by the immune system to stimulate the proliferation of defence cells) increases rapidly in the bloodstream. The increase in the number of neutrophils (a type of white blood cell) often lasts for up to 6 hours after the end of the exercise session. This physiological response to stress caused by exercise is followed, during the recovery period, by a drop in the number of leukocytes in the bloodstream to a level below that measured at the start of the exercise session.

Although exercise transiently increases markers of inflammation, including several cytokines (interleukins, chemokines, interferons, and others), at rest, people who exercise regularly have lower blood levels of these pro-inflammatory proteins than people who exercise little or not at all or who are obese. Regular exercise therefore appears to moderate the inflammatory response and promote an anti-inflammatory environment in the body. The persistent increase in markers of inflammation (chronic inflammation) is linked to several conditions and diseases, including obesity, osteoarthritis, atherosclerosis and cardiovascular disease, chronic kidney disease, liver disease, metabolic syndrome, insulin resistance, type 2 diabetes, chronic obstructive pulmonary disease, dementia, depression, and various types of cancers. In short, exercise reduces the negative effects on the immune system of a recognized factor that is diabetes and the associated insulin resistance.

It is known that in severe forms of COVID-19 an exaggerated inflammatory reaction called “cytokine storm” destroys the cells of the pulmonary endothelium that allow oxygenation of the blood and body. Could regular exercise that provides a less inflammatory environment protect us in the event of a SARS-CoV-2 virus infection? This has not been demonstrated, but it is certainly a hypothesis that will need to be examined. Moreover, it seems that in the elderly, immune aging (also called “immunosenescence”) is associated with a decline in the cells that regulate the immune response. It is because of this decline that we observe an increase in immune disorders such as autoimmune diseases and an increase in cancers. However, the cytokine storm would be secondary to the lack of control by these cells. A healthy immune system would be less likely to lack these “regulatory” cells.

Suppression of immunity in athletes: Myth or reality?
In recent decades, an idea has taken root in the scientific literature according to which aerobic exercise, particularly if it is vigorous and of long duration, can interfere with immunocompetence, i.e. the body’s ability to produce a normal immune response in response to exposure to an antigen. This idea is now increasingly questioned and has even been called a myth by some researchers. This hypothesis dates from the early 20th century, when fatigue was believed to contribute to infections that caused pneumonia, but it was not until the 1980s–1990s that studies verified this assertion with professional and amateur athletes. In general, it is increasingly certain that it is “psychological” stress rather than physical stress that is immunosuppressive. For example, a study in the 1980s among medical students showed that immune capacity collapsed within 24 to 48 hours of exams. The “mental” stress on the eve of competitions could be the comparison. Exercise is a great stress reliever for most people.

One of the studies indicated that one third of the 150 runners participating in the 1982 Two Oceans ultramarathon (56 km) in South Africa reported symptoms of upper respiratory tract infection (runny nose, sore throat, sneezing) within two weeks of the race. The control group reported half as many symptoms of upper respiratory tract infection than runners. Similar results were obtained from athletes who participated in the Los Angeles Marathon (42 km) in 1987. Among the 2311 participants who completed the race and who had not reported symptoms of infection in the week before the race, 12.9% reported symptoms of infection in the week following the race. Only 2.2% of participants who dropped out of the race (for reasons other than health reasons) reported symptoms of infection in the week after the race. Another study conducted at the same time did not find an association between aerobic exercise and the risk of upper respiratory tract infection for runs over shorter distances, namely 5 km, 10 km, and 21 km (half marathon). This suggested that the risk of infections increases only after exercising for a very long period of time.

The major problem with these studies is that they are questionnaire-based and none of the infections reported by athletes were confirmed in the laboratory. In a 2007 study, researchers took swabs and tested athletes who reported symptoms of upper respiratory tract infection over a period of 5 months. Only 30% of the cases reported by the participants were associated with the presence of viruses, bacteria, or mycoplasmas. These results suggest that the symptoms experienced by athletes in previous studies may not have been caused by infection, but rather by other causes, including allergies, asthma, inflammation of the mucous membranes, or trauma to the epithelial cells of the airways caused by increased breathing or exposure to cold air.

The decrease in leukocytes in the bloodstream that is observed after exercise has led to the so-called “open window” hypothesis that intense exercise causes transient immunosuppression during the recovery period. During this “open window”, athletes would be more susceptible to viral and bacterial infections. Another hypothesis would be that of the recruitment of white blood cells to repair small damage to the muscles. Indeed, tissue damage, whether mechanical or infectious, causes the release of cytokines, which “call” the defences to “see what happens.” Yet, contrary to the studies cited above, recent studies indicate that exercise is rather associated with a reduction in the incidence of infections. There are as many epidemiological studies that show that regular exercise is associated with a reduction in infections as there are that show that regular exercise is associated with an increase in infections, but the former are less taken into account than the latter in the literature on exercise immunology.

For example, a Swedish study of 1509 men and women aged 20 to 60 found that high levels of physical activity are associated with a reduced incidence of upper respiratory tract infections. Studies of ultramarathon runners, one of the most taxing sports, have shown that these people report fewer days of absence from school or work due to illness compared to the general population. For example, the average number of sick days reported annually was 1.5 days in a study of 1212 ultramarathon runners and 2.8 days in another study of 489 161-km ultramarathon runners, while that year the number of sick days reported in the American population was 4.4 days. An often overlooked aspect of outdoor exercise is its vitamin D intake with exposure to the sun. The longer the routes, the greater the exposure and endogenous skin production of vitamin D. Vitamin D intake would be beneficial for the regulatory cells of the immune system.

In summary, contrary to the immunosuppression (“open window”) hypothesis, regular exercise can be beneficial for the immune system, or at least not harmful. Exercise does not increase the risk of diagnosed opportunistic infections. Exercise can improve the immune response to viruses, bacteria, and other antigens. Regular physical activity and frequent exercise may reduce or delay the aging of the immune system.

To prevent cardiovascular disease, medication should not be a substitute for improved lifestyle

To prevent cardiovascular disease, medication should not be a substitute for improved lifestyle

OVERVIEW

  • Cardiovascular disease dramatically increases the risk of developing serious complications from COVID-19, again highlighting the importance of preventing these diseases in order to live long and healthy lives.
  • And it is possible! Numerous studies clearly show that more than 80% of cardiovascular diseases can be prevented by simply adopting 5 lifestyle habits (not smoking, maintaining a normal weight, eating a lot of vegetables, exercising regularly, and drinking alcohol moderately).

The current COVID-19 pandemic has exposed two major vulnerabilities in our society. The first is, of course, the fragility of our health care system, in particular everything related to the care of the elderly with a loss of autonomy. The pandemic has highlighted serious deficiencies in the way this care is delivered in several facilities, which has directly contributed to the high number of elderly people who have died from the disease. Hopefully, this deplorable situation will have a positive impact on the ways of treating this population in the future.

A second vulnerability highlighted by the pandemic, but much less talked about, is that COVID-19 preferentially affects people who present pre-existing conditions at the time of infection, in particular cardiovascular disease, obesity and type 2 diabetes. These comorbidities have a devastating impact on the course of the disease, with increases in the death rate of 5 to 10 times compared to people without pre-existing conditions. In other words, not only does poor metabolic health have a disastrous impact on healthy life expectancy, it is also a significant risk factor for complications from infectious diseases such as COVID-19. We are therefore not as helpless as we might think in the face of infectious agents such as the SARS-CoV-2 coronavirus: by adopting a healthy lifestyle that prevents the development of chronic diseases and their complications, we simultaneously greatly improve the probability of effectively fighting infection with this type of virus.

Preventing cardiovascular disease
Cardiovascular disease is one of the main comorbidities associated with severe forms of COVID-19, so prevention of these diseases can therefore greatly reduce the impact of this infectious disease on mortality. It is now well established that high blood pressure and high blood cholesterol are two important risk factors for cardiovascular disease. As a result, the standard medical approach to preventing these diseases is usually to lower blood pressure and blood cholesterol levels with the help of drugs, such as antihypertensive drugs and cholesterol-lowering drugs (statins). These medications are particularly important in secondary prevention, i.e. to reduce the risk of heart attack in patients with a history of cardiovascular disease, but they are also very frequently used in primary prevention, to reduce the risk of cardiovascular events in the general population.

The drugs actually manage to normalize cholesterol and blood pressure in the majority of patients, which can lead people to believe that the situation is under control and that they no longer need to “pay attention” to what they eat or be physically active on a regular basis. This false sense of security associated with taking medication is well illustrated by the results of a recent study, conducted among 41,225 Finns aged 40 and over. By examining the lifestyle of this cohort, the researchers observed that people who started medication with statins or antihypertensive drugs gained more weight over the next 13 years, an excess weight associated with an 82% increased risk of obesity compared to people who did not take medication. At the same time, people on medication reported a slight decrease in their level of daily physical activity, with an increased risk of physical inactivity of 8%.

These findings are consistent with previous studies showing that statin users eat more calories, have a higher body mass index than those who do not take this class of drugs, and do less physical activity (possibly due to the negative impact of statins on muscles in some people). My personal clinical experience points in the same direction; I have lost count of the occasions when patients tell me that they no longer have to worry about what they eat or exercise regularly because their levels of LDL cholesterol have become normal since they began taking a statin. These patients somehow feel “protected” by the medication and mistakenly believe that they are no longer at risk of developing cardiovascular disease. This is unfortunately not the case: maintaining normal cholesterol levels is, of course, important, but other factors such as smoking, being overweight, sedentary lifestyle, and family history also play a role in the risk of cardiovascular disease. Several studies have shown that between one third and one half of heart attacks occur in people with LDL-cholesterol levels considered normal. The same goes for hypertension as patients treated with antihypertensive drugs are still 2.5 times more likely to have a heart attack than people who are naturally normotensive (whose blood pressure is normal without any pharmacological treatment) and who have the same blood pressure.

In other words, although antihypertensive and cholesterol-lowering drugs are very useful, especially for patients at high risk of cardiovascular events, one must be aware of their limitations and avoid seeing them as the only way to reduce the risk of cardiovascular events.

Superiority of lifestyle
In terms of prevention, much more can be done by addressing the root causes of cardiovascular disease, which in the vast majority of cases are directly linked to lifestyle. Indeed, a very large number of studies have clearly shown that making only five lifestyle changes can very significantly reduce the risk of developing these diseases (see Table below).

The effectiveness of these lifestyle habits in preventing myocardial infarction is quite remarkable, with an absolute risk drop to around 85% (Figure 1). This protection is seen both in people with adequate cholesterol levels and normal blood pressure and in those who are at higher risk for cardiovascular disease due to high cholesterol and hypertension.

Figure 1. Decreased incidence of myocardial infarction in men combining one or more protective factors related to lifestyle. The comparison of the incidences of infarction was carried out in men who did not have cholesterol or blood pressure abnormalities (upper figure, in blue) and in men with high cholesterol levels and hypertension (lower figure, in orange). Note the drastic drop in the incidence of heart attacks in men who adopted all 5 protective lifestyle factors, even in those who were hypertensive and hypercholesterolemic. Adapted from Åkesson (2014).

Even people who have had a heart attack in the past and are being treated with medication can benefit from a healthy lifestyle. For example, a study conducted by Canadian cardiologist Salim Yusuf’s group showed that patients who modify their diet and adhere to a regular physical activity program after a heart attack have their risk of heart attack, stroke and mortality reduced by half compared to those who do not change their habits (Figure 2). Since all of these patients were treated with all of the usual medications (beta blockers, statins, aspirin, etc.), these results illustrate how lifestyle can influence the risk of recurrence.

Figure 2. Effect of diet and exercise on the risk of heart attack, stroke, and death in patients with previous coronary artery disease. Adapted from Chow et al. (2010).

In short, more than three quarters of cardiovascular diseases can be prevented by adopting a healthy lifestyle, a protection that far exceeds that provided by drugs. These medications must therefore be seen as supplements and not substitutes for lifestyle. The development of atherosclerosis is a phenomenon of great complexity, which involves a large number of distinct phenomena (especially chronic inflammation), and no drug, however effective, will ever offer protection comparable to that provided by a healthy diet, regular physical activity, and maintenance of a normal body weight.