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Science News

Dietary Flavonoids May Lower Parkinsonís Risk

Men who consume high amounts of flavonoids — plant pigments abundant in foods such as berries, tea, and apples — may lower their risk of Parkinson’s disease (PD), according to a new study published in the April 10, 2012 issue of Neurology.  However, the protective effects of flavonoids do not appear as strong for women, suggesting gender-specific differences in Parkinson’s disease risk.

Prior research has shown that some flavonoids protect dopamine-producing neurons (the same ones lost in Parkinson’s) from cell damage and death, and from forming toxic α-synuclein fibrils.  These findings suggested that flavonoids could slow or prevent the loss of dopamine-producing neurons in PD.  However, those experiments were conducted using cells in petri dishes, and scientists did not know whether flavonoids would have the same effects in people.  When a person eats flavonoid-rich foods, the digestive process may break down the flavonoids into inactive compounds.  And even if intact flavonoids make it into the bloodstream, they may not be able to enter the brain, where the dopamine-producing neurons reside.

To find out whether people with a high dietary flavonoid intake show a reduced risk of PD, researchers led by Xiang Gao, M.D., Ph.D., at Harvard Medical School analyzed the diets and medical histories of 80,336 female registered nurses and 49,281 male health professionals.  The women and men were enrolled in two separate long-term studies, the Nurses’ Health Study and the Health Professionals Follow-up Study, which began in 1976 and 1986, respectively.  Every four years, participants in both studies completed a questionnaire that asked about their lifestyle, including diet and health status.

The questionnaires asked how often during the previous year the participants had consumed a particular amount of a food item (for example, half a cup of strawberries), with nine possible responses ranging from “never” to “six or more times per day.”  Based on these responses, Dr. Gao and colleagues calculated the total flavonoid intake for each individual, as well as his or her intake of specific flavonoids.  Then, they examined medical histories to determine which participants had developed Parkinson’s.

Results

  • 805 participants (438 men and 367 women) developed PD during 20–22 years of follow-up.
  • Men who consumed the highest levels of total flavonoids (80th percentile and above) had a 40 percent lower PD risk than those who consumed the least (20th percentile and below).
  • The researchers found no significant relationship between total flavonoid consumption and PD risk in women.
  • Men who ate five or more servings of apples per week showed a 46 percent reduced risk of PD compared with those who ate less than one apple a month.  No similar effect was observed for women eating apples.
  • Men and women who had a high intake of a specific class of flavonoids known as anthocyanins, abundant in berries, lowered PD risk by about 24 percent.

What Does It Mean?

This study suggests that a person’s diet, specifically their flavonoid intake, may influence PD risk.  In particular, high consumption of berries, which are rich in anthocyanins, appears to slightly lower PD risk for both men and women.  These results are consistent with previous studies in which animals fed blueberry or strawberry extract showed increased dopamine release and reduced neural inflammation in the brain.

Men who ate high amounts of apples or of total flavonoids showed a reduced risk of PD, but no such relationships were observed for women.  This finding reinforces other studies that have shown gender differences in several risk and protective factors for PD.  Although the biological basis for these differences is unclear, one possibility is that men’s and women’s bodies break down, or metabolize, flavonoids differently. 

The researchers were careful to control for lifestyle factors, such as smoking, caffeine intake, medications, and alcohol consumption that might skew their results.  However, they did not control to Mediterranean diet adherence, which they reported was associated with lower PD risk in these cohorts.

Also, less obvious factors may have resulted in a false association between flavonoid intake and PD risk.  As in all studies that use self-reported questionnaires, errors may arise from incorrectly reported data.  Also, it’s possible that men and women may answer the same food frequency questionnaire differently.  Finally, the study consisted primarily of white health professionals; therefore, the results may not be generalizable to all populations.  Although a diet rich in fruits and vegetables is certainly advisable from a general health standpoint, further confirmation from additional epidemiological studies is needed to determine whether berries and apples can indeed lower PD risk.

Reference: Gao, X., Cassidy, A., Schwarzschild, M. A., Rimm, E. B., Ascherio, A. Habitual intake of dietary flavonoids and risk of Parkinson disease. Neurology, April 10, 2012, 78(15): 1138–1145.

 

Source Date: Apr 27 2012