Cardiovascular mortality increases during the holiday season

Seasonal variation in mortality rates has been known for a very long time (Hippocrates described it around 400 BC!) and is generally characterized by a greater number of deaths occurring during cold seasons than during warm seasons. In Quebec, for example, weekly death statistics collected during the years without a major epidemic (such as the COVID‑19 pandemic in 2020) show that mortality is highest during the first and last weeks of the year (around 1,500 deaths each) and lowest during the summer period, from July to September (around 1,100 deaths per week).

Cardiovascular mortality
Cardiovascular diseases are a major cause of mortality and several studies conducted in Europe, Asia, Oceania (Australia, New Zealand), and North America (United States and Canada) have unsurprisingly observed a higher incidence of mortality related to these diseases during the cold season. Colder weather activates a sympathetic peripheral vasoconstriction response, as well as an increase in blood pressure and heart rate, thus increasing the risk of cardiovascular events, particularly in those who are initially at higher risk due to age, a history of cardiovascular diseases or the presence of cardiometabolic abnormalities (overweight, hypertension, hypercholesterolemia) (see our article on this subject). It has also been suggested that certain physiological stresses (e.g. shovelling snow) as well as the higher incidence of respiratory infections typical of the winter season may increase the incidence and/or severity of myocardial infarction and stroke, particularly in older people.

On the other hand, a higher incidence of cardiovascular mortality has also been observed in regions with much milder winter temperatures (10ºC and above), such as Los Angeles (see Figure 1) and Taiwan, suggesting that factors other than cold contribute to this phenomenon.

Figure 1. Monthly variation in coronary mortality in Los Angeles (USA). From Kloner et al. (1999).

The holiday season…and heart attacks
A more detailed analysis of these seasonal variations in cardiovascular disease-related deaths has identified two main events that may contribute to the excess mortality observed during the winter season. In this study, which has become a classic, the examination of the distribution of 53 million deaths that occurred daily during the period between 1973 and 2001 showed that the winter mortality peak is particularly pronounced for two specific periods, namely Christmas (December 25 and 26) and New Year’s Day (January 1) (see Figure 2).

Figure 2. Excess cardiovascular mortality during the holiday season. The red line shows the sum of the number of deaths from cardiovascular disease in the United States for each day of the year during the study period (1973–2001). The dashed regression line shows the average number of daily deaths expected if mortality varies with the seasons but is not affected by holidays. Note the higher-than-expected number of deaths during the Christmas and New Year periods. From Phillips et al. (2004).

The influence of the holiday season on the increase in cardiovascular mortality has also been observed in other countries in the northern hemisphere, such as Norway and Sweden, but not in Australia (where Christmas occurs during the summer), which could suggest an influence of cold temperatures on the increased risk of death. On the other hand, one study reported an increase in cardiovascular mortality during the holiday season in New Zealand, a country in the southern hemisphere where Christmas is also celebrated in the summer, and it is therefore unlikely that the cold is the main culprit for the increase in the number of deaths at Christmas and New Year’s. In fact, data collected in the United States indicate that the increase in cardiovascular mortality during the holiday season is observed in both the cold northern regions of the country and the southern regions (and is even slightly higher in the southern states).

The excess mortality associated with Christmas and New Year’s Day is particularly striking when looking more specifically at deaths occurring in the emergency department or noted upon arrival at the hospital (Figure 3). It is also interesting to note that although cardiovascular mortality accounts for the majority of these deaths occurring during Christmas and New Year’s Day (Figure 3A), the influence of the holiday season does not appear to be limited to cardiac events, as a similar pattern is observed for natural deaths of non-cardiovascular origin (Figure 3B). Overall, these holidays are estimated to be characterized by an incidence of mortality from cardiovascular and noncardiovascular natural causes that is approximately 4% higher than normal and are estimated to have been responsible for 42,325 excess deaths in the United States between 1973 and 2001.

Figure 3. Daily variation in sudden cardiovascular (A) and non-cardiovascular (B) mortality during December and January in the United States. Values ​​represent deaths occurring in the emergency department or recorded upon arrival at the hospital. The dashed regression line indicates the average number of daily deaths expected if mortality were unaffected by holidays. From Phillips et al. (2004).

Mortality from natural causes in emergency departments or before hospital arrival thus shows distinct peaks around Christmas and New Year’s Day (Figures 4A and 4B), such that there are more of these sudden deaths on Christmas, Boxing Day, and New Year’s Day than on any other day of the year. In contrast, deaths that occur in other settings (hospitalized patients, nursing homes, or other locations) do not show two distinct peaks during the holidays, but rather a small, more diffuse peak that begins at Christmas and extends for about two weeks after the New Year (Figure 4C).

Figure 4. Daily variation in total natural mortality during December and January in the United States by location of death. Values ​​represent the number of total natural deaths (excluding accidents and suicides) that occurred in the emergency department, were recorded upon arrival at the hospital, or occurred at other locations. Note the sharp Christmas and New Year peaks in both emergency department and hospital arrival deaths, while deaths occurring outside of these settings have a diffuse distribution, starting at Christmas and ending in mid-January. To facilitate comparison, the figures have the same ratio scale, i.e. the highest value on the y-axis is 1.4 times the mean mortality level in each figure. From Phillips et al. (2010).

Possible mechanisms
Several hypotheses have been proposed to explain the underlying reasons for the peak in deaths (cardiovascular or other) that occur during the end-of-year festivities. So far, none of these possibilities have been clearly demonstrated, but some of them are more plausible and deserve to be seriously considered if we want to prevent, or at least reduce, the negative impact of the holidays on excess winter mortality:

1. Delayed health care consultations. Given the social importance of Christmas and New Year celebrations, some people may ignore symptoms of illness (or attribute them to stress or overindulgence in food or alcohol) to avoid disrupting the festivities. Such delays in consulting medical professionals are likely to worsen patients’ conditions and increase the risk of sudden death (cardiac or other) upon arrival at the hospital, as observed in the study (Figure 3). The deterioration in the health status of patients admitted to hospital due to these consultation delays could also explain the excess mortality observed in the weeks following the end-of-year festivities (Figure 4C).
   
2. Holiday emergency department overcrowding and/or reduced staffing. The holiday season is a particularly conducive time for emergency department overcrowding (due in part to respiratory infections and gastroenteritis), and this overcrowding of emergency departments does not spare American hospitals. The researchers noted that this upward trend in emergency department overcrowding coincides with an increase in the magnitude of the Christmas and New Year’s effects on excess mortality and may therefore contribute to this phenomenon. It is also possible that the reduction in medical staffing typical of the holiday season may play a role.
   
3. Emotional stress. Patients may be more stressed than usual due to the many obligations associated with the holiday season, whether financial (buying gifts, food, travel expenses, entertainment, decorating) or personal (receiving guests, preparing meals for several guests, unwanted interactions with certain people, etc.). Since many studies have established a strong link between certain stressful events and cardiovascular mortality, it is likely that holiday stress may contribute to the excess mortality observed during this period. In this sense, it was observed that during the celebrations of the year 2000, when the arrival of the new millennium was more stressful than usual due to various beliefs (terrorist attacks, end of the world or even the famous “year 2000 bug”), deaths from heart attacks increased significantly compared to “normal” New Year’s celebrations in the years before and after 2000. On the other hand, emotional stress is not considered a risk factor for most diseases other than cardiovascular diseases and therefore cannot explain the mortality peaks at Christmas and New Year’s associated with these diseases (Figure 3B).
   
4. Abuse of food and alcohol. Although many people indulge in excesses during the holidays, it is unlikely that this alone is responsible for the increased mortality at Christmas and New Year’s. For one thing, Thanksgiving, a holiday during which Americans eat and drink as much or more than at Christmas or New Year’s, is not associated with increased mortality. For another, similarly to the role of stress mentioned earlier, although it has been suggested that overeating can trigger heart attacks in some at-risk individuals, there is no plausible explanation for linking overeating to mortality from other diseases.

In short, excess mortality associated with the holiday season remains a poorly understood phenomenon. In the current state of knowledge, the most likely hypothesis remains that of the delay in medical consultation, where some patients minimize the seriousness of their illnesses so as not to disrupt the festivities. By waiting until the last minute to go to the hospital, it is often too late and the risk of sudden death becomes higher than normal. In the short term, going to the emergency room as quickly as possible in the event of an illness, whether cardiac or otherwise, can undoubtedly ruin a Christmas or New Year’s party; in the longer term, however, this decision can save your life and allow you to enjoy these moments of celebration for years to come.