Older adults whose diets included only small amounts of flavonoid-rich foods, such as berries, apples and tea, were two to four times more likely to develop Alzheimer's disease and Alzheimer’s related dementias over 20 years compared with people whose intake was higher. This is according to a new study from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.
The study of 2,800 people aged 50 and older examined the long-term relationship between eating foods containing flavonoids and risk of Alzheimer's disease (AD) and related dementias.
While many studies have looked at links between diet and dementias over short periods of time, this looked at the association over 20 years.
What are flavonoids?
Flavonoids are bioactive compounds in fruits, vegetables and other plant foods. They’re categorized into several subclasses, each one residing in certain foods and having specific health properties.
Flavonoids most commonly consumed include anthocyanins (berries, red grapes, red cabbage, pears), flavan-3-ols (green tea, cocoa), flavonols (onions, kale, broccoli), flavanones (citrus fruit), flavones (parsley, celery) and isoflavones (soybeans, legumes).
Many flavonoids have strong antioxidant and anti-inflammatory properties and, as such, are thought to protect brain cells from damage.
The findings
The research team determined that a low intake of three types of flavonoids was linked to higher risk of dementia when compared to the highest intake. Specifically:
- A low intake of flavonols (found in apples, pears and tea) was associated with twice the risk of developing AD related dementia
- A low intake of anthocyanins (in blueberries, strawberries and red wine) was associated with a four-fold risk of developing AD related dementias
- A low intake of flavonoid polymers (in apples, pears, and tea) was associated with twice the risk of developing AD related dementias.
The results were similar for risk of developing Alzheimer’s disease.
About the study
To arrive at their conclusions, the researchers analyzed six types of flavonoids and compared long-term intake levels with the number of AD and ADRD diagnoses later in life. They found that a low intake of three different flavonoids was linked to higher risk of dementia when compared to the highest intake. Examples of the levels studied included:
- A low intake was equal to no berries (anthocyanins) per month, roughly one-and-a-half apples per month (flavonols) and no tea (flavonoid polymers).
- A high intake was equal to roughly 7.5 cups of blueberries or strawberries (anthocyanins) per month, 8 apples and pears per month (flavonols) and 19 cups of tea per month (flavonoid polymers).
People who may benefit the most from consuming more flavonoids are people at the lowest levels of intake, and it doesn't take much to improve levels. A cup of tea a day or some berries two or three times a week would be adequate, the researchers said.
The also said age 50, the approximate age at which data was first analyzed for participants, is not too late to make positive dietary changes. The risk of dementia really starts to increase over age 70. When you’re approaching 50 or just beyond, it is time to start thinking about a healthier diet if you haven't already.
Caveats
There are some limitations to the study, including the use of self-reported food data from food frequency questionnaires, which are subject to errors in recall.
The findings are generalizable to middle-aged or older adults of European descent. Factors such as education level, smoking status, physical activity, body mass index and overall quality of the participants' diets may have influenced the results, but researchers accounted for those factors in the statistical analysis.
Finally, due to its observational design, the study does not prove a causal relationship between flavonoid intake and the development of Alzheimer’s disease or its related dementias.
Source: The American Journal of Clinical Nutrition, April 22, 2020.
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