Dietary Inflammatory Index
Several studies suggest that the nature of the foods we eat can greatly influence the degree of chronic inflammation and, in turn, the risk of chronic disease, including cardiovascular disease. For example, a pro-inflammatory diet has been associated with an increased risk of cardiovascular disease, with a 40% increase in risk in people with the highest index (see our article on the subject).

Pro-inflammatory diet and risk of dementia
In order to see if there is an association between a diet that promotes systemic inflammation and the risk of developing dementia, 1,059 elderly people residing in Greece were recruited as part of the study Hellenic Longitudinal Investigation of Aging and Diet (HELIAD). Only people without a diagnosis of dementia at the start of the study were included in the cohort. The inflammatory potential of the participants’ diet was estimated using the Dietary Inflammatory Index (DII) based on the known effect of various foods on the blood levels of inflammatory markers . The main pro-inflammatory foods are red meat, deli meats, refined flour, added sugars, and ultra-processed foods. Some of the main anti-inflammatory foods are vegetables, fruits, whole grains, tea, coffee, and red wine.

After a follow-up of 3 years on average, 62 people were diagnosed with dementia. Participants who had the diet with the highest inflammatory index had a three-fold higher risk of developing dementia at the end of the study, compared to those with the least inflammatory index. In addition, there appears to be a dose-response relationship, with an increased risk of dementia that increases by 21% for each unit of the inflammatory index.

Inflammation, interleukin-6, and cognitive decline
The study in Greece is not the first to be conducted on the impact of a pro-inflammatory diet on the incidence of dementia. In a Polish study of 222 postmenopausal women, those with cognitive deficits had significantly higher blood levels of interleukin-6 (IL-6; a marker of inflammation), were less educated, and were less physically active, compared to women with normal cognitive functions. Postmenopausal women who had a pro-inflammatory diet were much more likely to have cognitive impairment compared to those who had an anti-inflammatory diet, even after adjusting for age, height, body mass index, level of education, and levels of physical activity. Each one-point increase in the dietary inflammatory index was associated with a 1.55-fold increase in the risk of cognitive impairment.

In addition to these studies, it is interesting to see that a meta-analysis of 7 prospective studies including 15,828 participants showed that there is an association between the concentration of IL-6 in the blood and the overall cognitive decline in the elderly. Participants who had the most circulating IL-6 had a 42% higher risk of suffering cognitive decline than those with low blood IL-6 levels.

Several studies have suggested that systemic inflammation (i.e., outside the central nervous system) may play a role in neurodegeneration, Alzheimer’s disease, and cognitive decline in older adults. People with Alzheimer’s disease and mild cognitive impairment tend to have high blood levels of markers of inflammation (IL-6, TNF-α, CRP). In addition, a study indicates that people who have elevated levels of markers of inflammation during midlife have an increased risk of cognitive decline in subsequent decades.

Since the studies described above are observational, they do not establish a causal link between inflammatory diet and dementia. They only show that there is an association. Further studies are needed in the future to establish a cause and effect relationship and identify the underlying molecular mechanisms.

Evidence from recent studies should encourage experts to more often recommend diets high in flavonoids that decrease systemic inflammation and are conducive to the maintenance of good cognitive health. Mediterranean-type diets or the hybrid MIND diet (Mediterranean-DASH Intervention for Neurodegenerative Delay) with an abundance of plants are particularly effective in reducing or delaying cognitive decline.