A new study has found that men who regularly consume foods rich in flavonoids, such as berries, apples, certain vegetables, tea and red wine, may significantly reduce their risk for developing Parkinson's disease. The study was published in the journal Neurology this week. It added that there was no such effect among women.
The research was led by Dr Xiang Gao, a nutrition research scientist at Harvard School of Public Health in the US, and Dr Aedin Cassidy, a professor of nutrition at University of East Anglia's Norwich Medical School in the UK.
Flavonoids are naturally occurring, bioactive compounds present in many plant-based foods and drinks. In this study, the main protective effect appeared to come from a subclass of flavonoids known as anthocyanins, which are present in berries such as blackcurrants and blackberries, and other fruits, and also certain vegetables, such as aubergines.
It is already known that regular consumption of certain flavonoids may lower the risk for developing a wide range of human diseases, such as high blood pressure, heart disease, dementia, and some cancers. Another study published in Stroke: Journal of the American Heart Association earlier this year found that the flavonoids in citrus fruits – particularly oranges and grapefruits – may lower a woman’s risk of stroke. However, it is the first to show the compounds may protect neurons against brain diseases such as Parkinson's.
Cassidy said, “This is the first study in humans to look at the associations between the range of flavonoids in the diet and the risk of developing Parkinson's disease and our findings suggest that a sub-class of flavonoids called anthocyanins may have neuroprotective effects.”
Parkinson's is a degenerative neurological disease where the death of certain cells in the brain means it does not have enough dopamine, which in turn affects ability to control movement so that it takes longer to do things. The disease is progressive, so symptoms, such as tremor, rigidity and slowness of movement, gradually get worse with time. The disease affects around one in 500 people, which equates to 127,000 people in the UK. There is no cure, and very few effective drug therapies.
For the study, the researchers analyzed data from 49,281 men who took part in the Health Professional Follow-up Study and 80,336 women who took part in the Nurses' Health Study. Both cohorts are based in the US. Over the 20 to 22 years of follow-up, 805 of the participants (438 men and 367 women), developed Parkinson's Disease.
The researchers looked at habitual intake of five major sources of flavonoid-rich foods (tea, berry fruits, apples, red wine, oranges, and orange juice), both in terms of total flavonoid intake, and also in terms of subclasses of flavonoids.
For the analysis, the researchers ranked participants according to flavonoid intake, into quintiles: that is the 20% with the lowest intake, then the 20% with the next lowest intake and so on, and after taking into account potential confounders such as age, lifestyle, and so on, looked at the link between the quintiles and risk for Parkinson's Disease.
They found that in men, participants in the highest quintile of total flavonoid intake had a significant 40% lower risk for Parkinson's Disease than those in the lowest quintile of total flavonoids. No such significant relationship for total flavonoids was seen in women.
However, pooled analyses (men and women together) that examined subclasses of flavonoids, did show some significant reductions in risk for Parkinson's. Gao explained, “Interestingly, anthocyanins and berry fruits, which are rich in anthocyanins, seem to be associated with a lower risk of Parkinson's disease in pooled analyses.”
The analysis showed that those participants who consumed the most anthocyanins had a 24% lower risk for developing Parkinson's disease compared to those who consumed the least. The most common source of anthocyanins in the participants' diet were strawberries and blueberries. “Participants who consumed one or more portions of berry fruits each week were around 25 per cent less likely to develop Parkinson's disease, relative to those who did not eat berry fruits,” said Gao.
Antioxidants help to neutralise free radicals – destructive by-products of metabolism in the body that can damage cell membranes and DNA. Brain cells are particularly sensitive to free radicals – which may help to explain the benefits revealed by the study.
Gao said these findings, together with the other potential health benefits of eating berry fruits shown in other studies, such as lowering blood pressure, suggest “it is good to regularly add these fruits to your diet”. He, Cassidy and colleagues said they can't rule out that these protective effects may have come from other compounds, and the findings must now be confirmed by other large epidemiological studies and clinical trials.
Dr Kieran Breen, director of research at Parkinson's UK, said the results look interesting, but there are still a lot of questions to answer: there is a lot “more research to do before we really know how important diet might be for people with Parkinson's”, he added.
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