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Source: CC0 Public Domain

An estimated 5.5 million Americans have Alzheimer's disease, and by 2020 that number could reach 16 million. More people die from Alzheimer’s disease than from breast and prostate cancer combined.

By nearly any measure, this is a major health problem. Because Alzheimer’s is a complex disease, it is difficult to pinpoint its causes, and even more difficult to treat. But a growing body of evidence demonstrates that lifestyle factors, such a diet and exercise, play a role.

A systematic review published earlier this year in The Journals of Gerontology: Medical Sciences investigated the link between physical activity and Alzheimer’s disease.

Neurology and geriatrics researchers from Finland and Sweden selected 24 prospective, observational, and intervention studies to include in their analysis. The studies measured the association between Alzheimer’s disease and a broad range of physical activities including walking, bicycling, bowling and work-related activities such as carpentry, shoveling, or lifting and yard work.

Their analysis found that people who were physically active were less likely to develop Alzheimer’s disease. Overall, 18 of the 24 studies found that exercise reduced participants’ risk.  

The researchers found that leisure activities were more likely to reduce the risks of Alzheimer’s disease compared with work-related physical activity. Their paper discusses a wide range of reasons why this could be true: People who work in more physical jobs are more likely to have lower education and socioeconomic status, and less cognitive stimulation. They also tend to be more sedentary when they are not at work and after retirement.

The researchers did note that the available data do not provide information about what types and how much exercise are required to reduce the risks or delay the onset of Alzheimer’s disease. But they note that physical activities—especially the leisure activities found to be beneficial in the review—likely provide social and cognitive stimulation that also help protect against Alzheimer’s disease.

A second systematic review published earlier this year in the International Journal of Neuroscience raised the question of whether diet influences the risk of developing Alzheimer’s disease. This review included 64 studies of more than 130,000 people in total.

The authors drew several conclusions. First, the nature of analyzing eating patterns and Alzheimer’s disease makes it difficult to develop any firm conclusions. It can be difficult to track everything that a study participant eats, and most patients experience brain changes due to Alzheimer’s disease long before showing any symptoms of the disease.

Despite the limitations of this type of analysis, the study authors found clear evidence that diet does influence Alzheimer’s disease. Of the 64 studies included in the paper, 50 revealed a significant association between the disease and diet.

It is important to note that the entire body of data did not provide enough information about specific types of food to prevent or cause Alzheimer’s disease. But individual studies included in the paper did identify some protective foods including fish, fruit, coffee and wine. The authors also found some evidence that a diet high in saturated fats may increase the risk of Alzheimer’s disease.

The take-home message: The evidence suggests that lifestyle factors such as diet and exercise can help to prevent—and also increase the risk of—Alzheimer’s disease. But it is also important to note that Alzheimer’s disease is influenced by a wide range of factors including genetics, social and cognitive interactions and more. And researchers still don’t understand how these factors intersect.  

References

Stephen, R., Hongisto, K., Solomon, A., Lönnroos, E.; Physical Activity and Alzheimer’s Disease: A Systematic Review. J Gerontol A Biol Sci Med Sci 2017; 72 (6): 733-739.

Yusufov, M., Weyandt, L., Piryatinsky, I.; Alzheimer's disease and diet: a systematic review. International Journal of Neuroscience 2017; 27 (2).

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