Parkinson-Berry Study Should Be Viewed Cum Grano Salis

A word of caution about a much-publicized study suggesting a neuroprotective benefit of eating a lot of anthocyanin-rich berries. Although the study, distributed by way of press release and scheduled to be presented at the upcoming AAN meeting, found a gee-whiz 40% reduction of Parkinson disease in men who ate a lot of berries, the absolute rates of disease had to be very small.

Among 49,281 men and 80,336 women followed up for 22 years, there were only 805 cases of PD—for an overall rate of disease at about 0.6%.* So the absolute rate reduction (which isn't given in the lay press reports) has to be tiny—probably less than 1%. For instance, if about 0.4% of men who ate a lot of berries developed PD, and 0.8% of men who didn't eat a lot of berries got PD, the relative risk reduction would equal an impressive-sounding 50%. However, the absolute risk reduction associated with berry eating would be only 0.4%.

Another head-scratching facet of this story is that the supposed neuroprotective effect of eating berries was seen only in men—a fact that suggests a statistical fluke rather than a sound finding. In fact, the only reason that this story has any credence is the speculation that anthocyanin, a flavanoid, has some neuroprotective, antioxidant effect—an effect that really shouldn't be confined to men.

All of that said, however: It probably doesn't hurt to eat a decent, weekly share of berries.

* About 500,000 people in the United States have PD, for an overall prevalence of about 0.2%.

Image of 1886 drawing of PD patient by neurologist Sir William Richard Gowers from Wikimedia Commons.