Antioxidant Diet May Not Prevent Stroke, Dementia
Participants answered questionnaires about how often and how much they ate 170 typical Dutch foods. The researchers looked up the antioxidant capacity of each food item, which had previously been determined by chemical analyses, and added up the capacity of all the food items to calculate each participant's antioxidant score.
"There are thousands of antioxidants in the diet, and some of them may have more antioxidant power," Devore explained. This calculation allowed the group to estimate the whole antioxidant measure, although it does not take into account how antioxidants in different food items could influence one another, she added.
"The typical Dutch diet tends to be a lot of meat, pork or beef, a lot of dairy, coffee and tea, and lower intakes of fruits and vegetables," Devore said. The diet in this older population probably did not change much over the 14-year follow-up, she added.
Between 1990, when the researchers conducted the food surveys and collected the first health reports, and 2004, 599 of the participants developed dementia and 601 had a stroke. There was no difference between the groups that had high and low antioxidant capacity and the rates of these diseases.
Devore and her colleagues also failed to find a connection between total diet antioxidant power and brain sizes among the 462 participants who got an MRI test.
These findings suggest that it is time to go back to studying individual antioxidants, but more comprehensively, Devore said.
A connection between vitamin C and vitamin E and reduced risk of stroke and dementia, respectively, has been found in a number of studies, but there are probably other antioxidants such as flavonoids found in foods including onions, peas and berries that could be important, Devore said.
For his part, Bowman thinks there could still be a connection between antioxidant capacity in the Dutch group and dementia and stroke risk, but the researchers are not seeing it because they used food questionnaires to evaluate antioxidant levels.
"An alternative approach would be to look at dietary signatures in the blood," Bowman said.
Measuring nutrient levels in the blood could not only give a direct indication of what is available to the brain, but it could help avoid the inaccuracies in what people say they eat and differences in how well individuals absorb what they eat, he added.
In a 2012 study, Bowman and his colleagues developed a test to measure the levels of a panel of nutrients in the blood and found a connection among elderly people between high levels of vitamins B, C, D, and E and improved cognitive function and larger brains.
Although this connection has to be studied more, Bowman is working to start a clinical trial to test whether increasing the level of vitamins C and E could indeed help protect the brain from diseases.