Fruit and vegetables contain many nutrients and minerals that play an important role in helping us maintain good health. Take flavonoids, for example. These are a group of naturally occurring compounds that are found in many foods – including citrus fruit, berries, red wine and even dark chocolate.
Flavonoids act as antioxidants, which help to prevent or slow damage to cells which may lead to diseases – such as cancer. They also reduce inflammation in the body, which is common in many chronic diseases – including neurodegenerative ones, such as Alzheimer’s or Parkinson’s disease.
Research shows that flavonoids are good for our brain health, with studies showing diets high in fruit and veggies may slow cognitive decline and lower dementia risk. And now, a recent study has suggested that people with Parkinson’s disease who consume diets high in flavonoids may live longer than those who don’t.
To conduct their study, a team of researchers analysed data from 121,700 female registered nurses and 51,529 male health professionals. They chose to look at these two groups because many aspects of their lifestyles which might influence their disease risk would be similar – such as activity levels, education and years in work. Information on their diets has been gathered every two to four years, beginning in 1975 for the women and 1986 for the men. The data from these groups has been used in many other high quality nutrition studies.
At the time when this new study was conducted, 599 of the women and 652 of the men had been diagnosed with Parkinson’s disease. From the foods these women and men reported consuming, it was possible to calculate their intake of flavonoids.
It was found that the men with Parkinson’s disease who ate the most flavonoids as part of their diet had a 47% lower risk of dying from any cause compared to men who consumed the least flavonoids in their diet. But for women, the amount of flavonoids they consumed in their diet had no effect on their risk of death from all causes. So the tentative conclusion from this study is that flavonoids may reduce the risk of men with Parkinson’s disease from dying, although not in women. It’s not currently known why the men saw greater benefit.
As with any observational nutrition study of this type – where researchers simply observe outcomes without trying to intervene in the group (such as intervening by having half of the group eat a specific diet) – it’s not possible to prove a causal link. In the case of the present study, a causal link would mean that eating more flavonoids directly reduces the risk of men with Parkinson’s disease from dying.
A main reason for not being able to prove causality is that other dietary and lifestyle factors may also have contributed to extending lifespan. The authors did compensate for this to some extent by making statistical adjustments for other potentially beneficial nutrients – such as beta-carotene and the antioxidant vitamins C and E – and for possibly damaging lifestyle factors such as smoking, being overweight and not exercising enough.
But this still doesn’t take into account many other dietary, lifestyle and genetic factors that could contribute to a person’s risk. One example is exposure to herbicides and pesticides.
One factor that did influence the study’s results was the type of flavonoids they looked at. There are many different types of flavonoids, and two groups – known as anthocyanins and flavan-3-ols – were found in this study to be most strongly linked to prolonging life. Anthocyanins give berries and red wine their red and purple colours, and flavan-3-ols are found at high levels in green tea.
But it’s not known how these flavonoids may benefit the brain. As with other degenerative brain disorders, the progression of Parkinson’s disease is likely to involve oxidative stress (when too many highly reactive molecules, called free radicals, are produced for antioxidant defences to handle) and brain inflammation. Many flavonoids, including anthocyanins and flavan-3-ols, have been shown in experimental studies to have antioxidant and anti-inflammatory properties.
Other mechanisms may also be involved. Flavonoids can have a positive effect on the gut microbiome, which may decrease the inflammation that contributes to Parkinson’s. Also, as Parkinson’s disease progresses, many neurological pathways such as the dopamine pathway are affected. Dopamine plays a vital role in regulating movement by the body. But the possible role of flavonoids in improving the functioning of these pathways is not known.
Though this study examined risk of death in people who already had Parkinson’s disease, other studies have also shown that diets high in flavonoids lower the risk of developing Parkinson’s disease. The benefit was also shown to be greater in men – although again it is not clear why.
While there are many factors that might have influenced the results of this latest study, there’s still a good body of evidence suggesting that diets rich in flavonoids can help protect against many degenerative brain disorders – including Parkinson’s disease. And fortunately for us, flavonoids are found in many fruits and vegetables that we can readily buy from our supermarket.
Richard Hoffman is the author of two books on the Mediterranean diet: The Mediterranean Diet: Health and Science (2011) and More Healthy Years – Why a Mediterranean Diet is best for you and for the planet (2020).