In a population study, scientists have found that consuming foods associated with a low Diet Inflammatory Index substantially lowers the risk of dementia [1].
Aging is accompanied by an increase in chronic, low-grade inflammation, known as inflammaging, which has been linked to multiple age-related diseases. Inflammaging promotes cancer, diabetes, cardiovascular diseases, and various types of dementia, such as the deadly Alzheimer’s disease. Age-related cognitive decline is of particular concern to geroscientists since the brain is the one organ that can never be replaced as a whole.
While modern medicine is usually pretty good at treating acute inflammation, countering inflammaging is a much harder task. Currently, no approved treatments exist, and inflammaging is not even in the International Classification of Diseases.
Not much to do except exercise and diet
Like with many age-related conditions, lifestyle interventions are the only available treatments. For instance, there are indications that aerobic exercise protects against inflammaging [2]; on the other hand, too much exercise can exacerbate local inflammation, such as in joints affected by osteoarthritis [3]. It has been known for years that some types of food are more inflammatory than others. For example, a plant-based diet has been found to lower inflammation in general and in rheumatoid arthritis in particular [4].
The Diet Inflammatory Index (DII) shows how various foods and nutrients contribute to inflammation. Based on hundreds of studies, it is widely accepted by the scientific community. Since inflammaging negatively affects many aspects of health, it is not surprising that previous studies have found that an anti-inflammatory diet substantially lowers the risk of cardiovascular diseases, colorectal cancer, and overall mortality [5, 6].
Three-fold increase in the risk of dementia
In this new paper, an international group of researchers ran a population study to determine how DII affects dementia incidence. 1059 healthy participants (no dementia at baseline) with a mean age of 73 were recruited through random population sampling. The mean follow-up period was 3 years, and the participants’ dietary habits were assessed via a detailed questionnaire.
The researchers controlled for several potentially confounding variables that have been associated with a risk of dementia: total energy intake, baseline mild cognitive impairment (MCI) score, education, sex, and a clinical comorbidity index that, in turn, included multiple conditions like hypertension and diabetes. Unfortunately, some other relevant variables, such as physical activity, smoking, and alcohol consumption, were not accounted for.
Over the course of the study, 62 of the participants developed dementia. DII score emerged as the main predictor: a 1-point increase in DII was associated with a 21% increase in the risk of dementia, and people in the highest DII tertile (that is, the people consuming the most pro-inflammatory diets) were three times as likely to develop dementia as people in the lowest tertile. The results were highly statistically significant.
Broad studies, broad variables
Population studies are tricky, mostly because there are too many variables to consider. They can produce widely varying and sometimes contradictory results, so they should be taken with a grain of salt; figurative salt, though, as salt intake promotes inflammation [7]. However, that does not make population studies worthless. When there is a critical mass of studies pointing in one direction, they can influence the scientific consensus.
It looks like on this particular topic, scientists are inching towards an agreement. The authors cite several previous studies, including a US-based population study of 7085 women that produced similar results (this study included people of both sexes) and other studies from France and Korea. A smaller Australian study, on the other hand, did not find an association between DII and global cognitive function.
In addition to the usual limitations of a population study, this one was characterized by a high rate of people who were not available for follow-up at the end of the study. The researchers do not cite specific reasons for that but maintain that this did not affect the robustness of the results.
Accruing evidence supports that diet plays a central role in the regulation of chronic inflammation, and dietary modulation of inflammaging might be a valuable preventive strategy for dementia and cognitive decline. In the present study, we were able to demonstrate that the inflammatory potential of diet, assessed using an easily applicable tool, was positively associated with the risk for dementia in community-dwelling non-demented older adults.
Conclusion
This population study bolsters the hypothesis that a low-inflammation diet can be protective against age-related cognitive decline. Though more research is needed, these results are in agreement with what we know about inflammation and aging.
Literature
[1] Charisis, S., Ntanasi, E., Yannakoulia, M., Anastasiou, C. A., Kosmidis, M. H., Dardiotis, E., … & Scarmeas, N. (2021). Diet Inflammatory Index and Dementia Incidence: A Population-Based Study. Neurology, 97(24), e2381-e2391.
[2] Nilsson, M. I., Bourgeois, J. M., Nederveen, J. P., Leite, M. R., Hettinga, B. P., Bujak, A. L., … & Tarnopolsky, M. A. (2019). Lifelong aerobic exercise protects against inflammaging and cancer. PloS one, 14(1), e0210863.
[3] Perez-Lasierra, J. L., Casajús, J. A., González-Agüero, A., & Moreno-Franco, B. (2021). Association of physical activity levels and prevalence of major degenerative diseases: Evidence from the national health and nutrition examination survey (NHANES) 1999–2018. Experimental Gerontology, 111656.
[4] Alwarith, J., Kahleova, H., Rembert, E., Yonas, W., Dort, S., Calcagno, M., … & Barnard, N. D. (2019). Nutrition interventions in rheumatoid arthritis: the potential use of plant-based diets. A review. Frontiers in nutrition, 6, 141.
[5] Shivappa, N., Godos, J., Hébert, J. R., Wirth, M. D., Piuri, G., Speciani, A. F., & Grosso, G. (2018). Dietary inflammatory index and cardiovascular risk and mortality—a meta-analysis. Nutrients, 10(2), 200.
[6] Shivappa, N., Godos, J., Hébert, J. R., Wirth, M. D., Piuri, G., Speciani, A. F., & Grosso, G. (2017). Dietary inflammatory index and colorectal cancer risk—a meta-analysis. Nutrients, 9(9), 1043.
[7] Zhu, H., Pollock, N. K., Kotak, I., Gutin, B., Wang, X., Bhagatwala, J., … & Dong, Y. (2014). Dietary sodium, adiposity, and inflammation in healthy adolescents. Pediatrics, 133(3), e635-e642.
