Antioxidants to prevent Alzheimer’s? Study reveals potential flavanol link

30 Jan 2020 --- Regular consumption of foods with the antioxidant flavonol, which is found in nearly all fruits, vegetables and tea, may lead to a reduced likelihood of developing Alzheimer’s in later years. This is the conclusion of a study published in this week’s Neurology issue in the American Academy of Neurology medical journal. While diet experts question the credibility of the study’s results – given the fact that it could not prove a biological, causal link – this study contributes to the body of literature finding that regular fruit and vegetable intake can yield long-term positive health effects.

“Consuming more fruits and vegetables and drinking more tea could be a fairly inexpensive and easy way for people to help stave off Alzheimer’s dementia. With the elderly population increasing worldwide, any decrease in the number of people with this devastating disease, or even delaying it for a few years, could have an enormous benefit on public health,” says study author Dr. Thomas M. Holland of Rush University in Chicago, US.

Following a healthful diet is known to be a good approach to chronic disease prevention rather than focusing on particular nutrients.The study involved 921 people without Alzheimer’s with an average age of 81, tracking their health states for six years. Every year, the test subjects submitted a questionnaire on how often they ate certain foods. The researchers also monitored other factors, such as their level of education, how much time they spent doing physical activities and how much time they spent doing mentally engaging activities, such as reading and playing games.

The researchers divided the study participants into five groups based on how much flavonol they had in their diets. The average amount of flavonol intake in US adults is about 16 to 20 mg per day. In the study, the lowest group had an intake of about 5.3 mg per day and the highest group consumed an average of 15.3 mg per day.

Using various tests, the researchers used various tests to determine that 220 of the research participants developed Alzheimer’s dementia during the study. The study also concluded that subjects in the highest flavonol group were 48 percent less likely to later develop Alzheimer’s dementia than those in the lowest group after adjusting for genetic predisposition, demographic and lifestyle factors. Of the 186 people in the highest group, 28 people (15 percent) developed Alzheimer’s dementia, compared to 54 people (30 percent) of the 182 people in the lowest group.

Unreliable methodology?
While presenting potentially significant results for future nutrition research, this study has been criticized for its methodology. “To estimate flavonol intake in this population, researchers used a type of food questionnaire, which is not the best tool to measure food intake, as it relies on what people remembered they ate over an entire year,” notes Dr. Ana Rodriguez-Mateos, Lecturer in Nutritional Sciences, Kings College, London, UK.

Dr. Ada Garcia, Lecturer in Public Health Nutrition, University of Glasgow, UK, also notes that relying on memory is particularly difficult in elderly participants because reduced cognitive function is a normal process of aging.

A cup of black tea can provide 15 mg of flavonols to diets.Besides this point, other researchers highlight that observed associations studies should not be confused with actual biological or causal links. “To give confidence in this observation, it must first be repeated in other groups. Many studies in the past have shown, however, that such observations do not replicate well. In general, one should be careful not to overstate the importance of such findings,” flags Professor Bart De Strooper, Director, UK Dementia Research Institute. 

The sentiment is echoed by Dr. James Pickett, Head of Research, Alzheimer’s Society, UK. “This new study in people is not definitive about whether flavonols can lower dementia risk and it doesn’t provide enough evidence to say that drinking tea and eating food rich in flavonols will ward off dementia,” he stresses.

Fluctuating flavonols
Flavonols are a type of flavonoid, a group of phytochemicals found in plant pigments known for its beneficial effects on health. They are found, for example, in onions (125 mg per 100 g – about 250 mg in an onion) or berries (42 mg per 100 g in elderberry). A cup of tea contains about 20 mg, although depending on how it is made, it can be anywhere between 2 and 40 g. 

“In the UK, people consume about 30 mg per day through tea alone – which is higher than the average intake of about 20 mg per day in Europe,” explains Professor Gunter Kuhnle, Nutrition and Food Science, University of Reading, UK. 

“Consuming isolated flavonols or extracts of flavonol rich foods, such as tea extracts, will not work in isolation to reduce risk of disease. Furthermore, high doses can also have negative effects on health,” warns Dr. Garcia.

Regardless, this study does add to the wide body of research that confirms long-standing health benefits increased fruit and vegetable consumption, affirms Catherine Collins, an NHS Dietitian.

“In the meantime, we can say for sure that eating a balanced diet, with lots of fruit and vegetables and getting enough exercise is a proven way to reduce your risk of dementia,” Dr. Pickett concludes.

By Anni Schleicher