In a new study, investigators find that good dietary habits do not necessarily reduce the risk of dementia later in life.
Jennifer L. Dearborn-Tomazos, MD
A team of investigators, led by Jennifer L. Dearborn-Tomazos, MD, Yale School of Medicine, identified the link between dietary patterns in midlife and cognitive function in later life in people without dementia.
“This study found that the dietary pattern of US adults at midlife was not associated with processing speed, word fluency, memory, or incident dementia in later life,” the authors wrote.
In the observation cohort, the investigators analyzed data collected between 1987-2017 of 13,588 community-dwelling people between the ages of 45-64 from Washington County, Maryland; Forsyth County, North Carolina; Jackson, Mississippi; and suburban Minneapolis, Minnesota. Each participant was part of the Atherosclerosis Risk in Communities study.
They derived a pair of dietary patterns scores from a 66-iten food frequency questionnaire using principal component analysis.
A Western dietary pattern was characterized by a higher consumption of meats and fried foods, while a healthier dietary pattern was characterized by higher amounts of fruits and vegetables.
The investigators used the results of 3 different cognitive tests—Digit Symbol Substitution Test, Word Fluency Test, and Delayed Word Recall—performed between 1990-1992, 1996-1998, and 2011-2013. The results were standardized and combined to represent global cognitive function.
The 20-year change in cognitive function was measured by textile of diet pattern score using mixed-effect models. The risk of incident dementia was also determined by textile of the diet pattern score.
Participants in the top third of Western and prudent diet patterns were considered adherent to their respective diets.
“Cognitive scores at baseline were lower in participants with a Western diet (z score for textile 3 [T3], −.17 [95% CI, −.20-−.14] vs T1, .17 [95% CI, .14-.20]) and higher in participants with a prudent diet (z score for T3, −0.09 [95% CI, −.12-−.06] vs T1, −.09 [95% −.12-−.06]),” the authors wrote. “Estimated 20-year change in global cognitive function did not differ by dietary pattern (difference of change in z score for Western diet, T3 vs T1: −.01 [95% CI, −.05-.04]; and difference of change in z score for prudent diet, T3 vs T1: .02 [95% CI, −.02-.06]).”
However, the risk of incident dementia, did not differ by dietary pattern (Western HR T3 vs T1, 1.06 [95% CI, .92-1.22]; prudent HR T3 vs T1, .99 [95% CI, .88-1.12]).
While healthy dietary patterns could protect against dementia and mild cognitive impairment, previous studies show that healthy dietary patterns are linked with increased brain volumes and reduced atrophy compared to less healthy dietary patterns.
However, the mechanisms behind the relationship between a healthy diet and improved brain health are not fully understood.
The plausible mechanisms include reduced vascular injuries and a reduction in Alzheimer pathology.
A healthy dietary pattern reduces hypertension, dysglycemia, hyperlipidemia, and chronic inflammation, which may reduce brain vascular injury. Also, through reduced oxidative stress, a healthy diet could reduce the accumulation of proteins involved in Alzheimer disease.
Midlife dietary pattern, compared with dietary pattern in later life, may have a stronger association with cognitive decline and dementia because chronic disease or the concern for chronic disease in later life may motivate individuals to improve their diet.