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Onset of Alzheimer’s disease (AD) was inversely associated with intake of flavonols, a subclass of flavonoids with antioxidant and anti-inflammatory properties, according to the study authors.
The rate of developing AD was reduced by 50% among individuals reporting high intake of kaempferol, a flavonol plentiful in leafy green vegetables, and by 38% for high intake of the flavonols myricetin and isorhamnetin, researchers said in a report published in Neurology.
The findings are from the Rush Memory and Aging Project (MAP), a large, prospective study of older individuals in retirement communities and public housing in the Chicago area that has been ongoing since 1997.
“Although there is more work to be done, the associations that we observed are promising and deserve further study,” said Thomas M. Holland, MD, of the Rush Institute for Healthy Aging in Chicago, and coauthors.
Those associations between flavonol intake and AD help set the stage for U.S. POINTER and other randomized, controlled trials that seek to evaluate the effects of dietary interventions in a more rigorous way, according to Laura D. Baker, PhD, associate professor of internal medicine at Wake Forest University, Winston-Salem, N.C.
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Dr. Laura D. Baker
“This kind of data helps us feel like we are looking in the right direction in the randomized, controlled trials,” Dr. Baker said in an interview.
Dr. Baker is an investigator in the U.S. POINTER study, which will in part evaluate the impact of the MIND diet, which has been shown to slow cognitive decline with age in a previously published MAP study.
However, in the absence of randomized, controlled trial data, Dr. Baker cautioned against “prematurely advocating” for specific dietary approaches when speaking to patients and caregivers now.
“What I say is, we know for sure that the standard American Heart Association diet has been shown in clinical trials to reduce the risk of heart disease, and in terms of brain health, if you can reduce risk of heart disease, you are protecting your brain,” she said in the interview.
The present MAP study linking a reduced rate of AD to flavonol consumption is believed to be the first of its kind, though two previous studies from the early 2000s did find inverse associations between incident AD and intake of flavonoids, of which flavonoids are just one subclass, said Dr. Holland and coinvestigators in their report.
Moreover, in a MAP study published in 2018, Martha Clare Morris, ScD, and coauthors concluded that consuming about a serving per day of green leafy vegetables and foods rich in kaempferol, among other nutrients and bioactive compounds, may help slow cognitive decline associated with aging.
To more specifically study the relationship between kaempferol and other flavonols and the development of AD, Dr. Holland and colleagues evaluated data for MAP participants who had completed a comprehensive food frequency questionnaire and underwent at least two evaluations to assess incidence of disease.
The mean age of the 921 individuals in the present analysis was 81 years, three-quarters were female, and over approximately 6 years of follow-up, 220 developed AD.
The rate of developing AD was 48% lower among participants reporting the highest total dietary intake of flavonols, compared with those reporting the lowest intake, Dr. Holland and coauthors reported.
Intake of the specific flavonols kaempferol, myricetin, and isorhamnetin were associated with incident AD reductions of 50%, 38%, and 38%, respectively. Another flavonol, quercetin, was by contrast not inversely associated with incident AD, according to the report.
Kaempferol was independently associated with AD in subsequent analyses, while there was no such independent association for myricetin, isorhamnetin, or quercetin, according to Dr. Holland and coinvestigators.
Further analyses of the data suggested the linkages between flavonols and AD were independent of lifestyle factors, dietary intakes, or cardiovascular conditions, they said in their report.
“Confirmation of these findings is warranted through other longitudinal epidemiologic studies and clinical trials, in addition to further elucidation of the biologic mechanisms,” they concluded.
The study was funded by grants from the National Institutes of Health and the USDA Agricultural Research Service. Dr. Holland and coauthors said that they had no disclosures relevant to their report.
SOURCE: Holland TM et al. Neurology. 2020 Jan 29. doi: 10.1212/WNL.0000000000008981.