Dementia Risk Tied to Quality of Plant-Based Diets

People who followed a high-quality plant-based diet had a lower risk of Alzheimer’s disease and other dementia, while those with a low-quality plant-based diet had a higher risk, prospective data showed.

At baseline, people who ate the most plant foods overall had a 12% lower risk of dementia over nearly 11 years of follow-up compared with those who ate the least (HR 0.88, 95% CI 0.85-0.92), reported Song-Yi Park, PhD, of the University of Hawaii at Manoa in Honolulu, and co-authors.

However, not all plant-based diets performed equally well. People with a high-quality plant-based diet at baseline had a lower dementia risk (HR 0.93, 95% CI 0.89-0.97), while those with a low-quality plant-based diet had a higher dementia risk (HR 1.06, 95% CI 1.01-1.10), Park and colleagues wrote in Neurology.

Compared with people whose diets remained stable over 10 years, those who shifted their eating habits to have a large decrease in low-quality plant foods over time had an 11% lower risk (HR 0.89, 95% CI 0.84-0.94), the researchers said. Those with a large increase in low-quality plant foods over that period had a 25% higher risk (HR 1.25, 95% CI 1.15-1.36).

The relationships between plant intake and dementia risk were generally similar by age group (under age 60 vs 60 and older at baseline), race and ethnicity, and APOE4 gene status.

“We found that adopting a plant-based diet, even starting at an older age, and refraining from low-quality plant-based diets were associated with a lower risk of Alzheimer’s and other dementias,” Park said in a statement. “Our findings highlight that it is important not only to follow a plant-based diet, but also to ensure that the diet is of high quality.”

Plant-based diets, especially those rich in high-quality plant foods, have been linked with lower risks of coronary heart disease and type 2 diabetes. Some studies have tied plant-based diets with less dementia risk; others have shown no relationship.

Plant-based eating patterns can encompass a wide variety of diets, including vegan, vegetarian, and omnivorous diets with small amounts of animal foods. To account for the quality of plant-based foods, diet indices have been developed. These include the overall plant-based diet index (PDI), the healthful plant-based diet index (hPDI), and the unhealthful plant-based diet index (uPDI).

The overall PDI prioritizes eating plant foods instead of animal products without assessing quality. The hPDI focuses on high-quality plant foods including whole grains, fruits, vegetables, vegetable oils, nuts, legumes, and tea/coffee. The uPDI includes less healthy plant foods like refined grains, fruit juices, potatoes, and added sugars. The hPDI has been associated with less risk of cognitive decline and lower mortality risk.

Park and colleagues studied data from 92,849 African American, Japanese American, Latino, Native Hawaiian, and white participants in the Multiethnic Cohort Study in Hawaii and California. They used a quantitative food frequency questionnaire to assess participants’ usual diet at cohort baseline in 1993 to 1996 and at 10-year follow-up in 2003 to 2008.

Participants had a mean age of 59.2 years at baseline and were followed for an average of 10.9 years. The researchers identified incident Alzheimer’s and related dementia using diagnostic codes in Medicare fee-for-service claims data.

Overall, there were 21,478 cases of incident Alzheimer’s disease or other dementia. In the smaller group of 45,065 participants who reported their diet again after 10 years, 8,360 had incident Alzheimer’s or dementia.

When researchers examined specific food groups, they found that a large decrease in four healthy plant food groups over 10 years — whole grains, vegetable oils, nuts, and tea/coffee — was associated with a higher risk of dementia by 11% to 15%, and a large increase in fruits was related to an 11% higher risk, compared with no dietary changes. Increased consumption of added sugars over 10 years also was associated with a 12% higher dementia risk.

Food frequency questionnaires are subject to measurement error, including random recall error, Park and co-authors acknowledged. Unknown risk factors and residual confounding also may have influenced results.