Contrary to previous research, a diet rich in antioxidants may not reduce a person’s risk for stroke or dementia, a new study says.

Researchers analyzed information from more than 5,300 people ages 55 and older living in the Netherlands. Participants answered questions about how often they ate certain foods, and their responses were used to calculate the total level of antioxidants in their diets.

Fourteen years later, about 600 people had developed dementia, and 600 had suffered a stroke. People who reported diets high in antioxidants were just as likely to develop dementia or have a stroke during the study period as individuals who consumed diets that were low in antioxidants. 

Interestingly, previous studies that used information from this same group of people found a link between consumption of vitamin E and a lower risk of dementia, and between consumption of vitamin C and a lower risk of stroke. Both vitamins are types of antioxidants.

While the new study looked at total antioxidant levels, regardless of the food source, it may be that the kind of food providing the antioxidants matters, said study researcher Elizabeth Devore of the Harvard Medical School in Boston.

In the current study, the difference between a diet high in antioxidants and a diet low in antioxidants was primarily linked to the amount of coffee and tea that people drank. (These beverages contain antioxidants called flavonoids.)

However, if people get most of their antioxidants from fruits, vegetables and nuts, the effect on dementia and stroke risk might be different, Devore said. For instance, a study published last year found that women who ate a lot of citrus fruits, such as oranges and grapefruits, were 19 percent less likely to have a stroke during a 14-year period compared to women who ate fewer of these fruits.

It's important to note that all of these studies only looked for associations and cannot demonstrate cause-effect links.

The new study was published on Feb. 20 in the journal Neurology.

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