Total Dietary Antioxidants Not Linked to Stroke, Dementia

February 21, 2013

No association was found between total dietary antioxidant intake and subsequent risk for dementia or stroke in a Dutch cohort study.

Noting that previous studies have suggested specific antioxidants may benefit stroke or dementia risk, the authors say the message from the current study is that total antioxidant intake is not as important as specific antioxidant sources.

"In general higher intake of fruit and vegetables appear to be good for stroke risk, and berries for better cognitive function. And we know these have other health benefits too," lead author, Elizabeth E. Devore, ScD, Harvard Medical School, Boston, Massachusetts, commented to Medscape Medical News.

Their findings are published online in the February 20 online issue of Neurology.

The Rotterdam Study

The current study used an existing cohort study — the Rotterdam Study — in older Dutch adults to look at the overall amount of antioxidant in an individual's diet and whether this showed any relationship with risk for stroke or dementia.

The Rotterdam study was established in 1990 to look at risk factors for chronic diseases in the elderly. The current study examined dietary questionnaires of 5395 dementia-free participants aged 55 years and older at the start of the study, which detailed intake of 170 specific foods eaten over the past year or so.

Although the food questionnaire was conducted only once, Dr. Devore said she thought this was adequate because most people were found to be eating a typical Dutch diet; it is "a pretty good assumption" that older people following a typical diet generally tend to continue to do that over the long-term.

The antioxidant quantities in the various foods were calculated with the use of the Antioxidant Food Table published by the Institute of Nutrition Research, University of Oslo, which includes measurements of 3000 foods worldwide. Then each individual was given an antioxidant score known as the ferric-reducing antioxidant power (FRAP) score.

Participants were followed up every 3 to 4 years over a 14-year period with screening tests for dementia (the Mini-Mental State Examination and Geriatric Mental State–Organic Level, as well as additional neuropsychological testing for those who screened poorly, with further evaluation by a neurologist or neuropsychologist, if necessary). They were also continuously monitored for incident dementia or stroke by computerized linkage to their digitalized medical records.

Results showed that during a median 13.8 years of follow-up, approximately 600 cases each of dementia and stroke were identified. In multivariable-adjusted models, no associations between dietary antioxidant scores and risk for dementia or risk for stroke were found.

Table. Risk for Neurologic Outcomes With Highest vs Lowest FRAP Score

Outcome Relative Risk (95% Confidence Interval) P Value for Trend
Dementia 1.12 (0.91 - 1.38) .3
Stroke 0.91 (0.75 - 1.11) .3

Antioxidant scores were also found to be unrelated to brain tissue volumes in a subgroup of people who underwent MRI.

No Role for Tea and Coffee?

Dr. Devore noted that in the current study, the major contributors to antioxidant intake were tea and coffee, which accounted for 90% of the variation in antioxidant intake within the population studied.

"The US Nurses' Health Study showed similar results to ours in that overall dietary antioxidant intake was not associated with any reduction in the decline of cognitive function, and coffee and tea also had a big contribution to antioxidant intake in that study. But it did show a reduced risk of cognitive decline with a high intake of berries."

Dr. Devore also pointed out that her group has previously published that a higher intake of vitamin E was associated with a reduced risk for dementia and Alzheimer's disease. "Also it has previously been shown that a high intake of vitamin C was linked to a reduced risk of ischemic stroke from this same Rotterdam database."

In an Italian study, overall antioxidant activity was associated with a reduced risk for ischemic stroke, she said, but in that study there was a higher intake of antioxidants from fruit and vegetables and alcoholic beverages and a lower contribution from coffee and tea. "High intakes of fruit and vegetables have been linked to reduced stroke risk in many previous studies," Dr. Devore added.

"These results appear to be telling us that it is not the overall antioxidant intake that matters but rather the specific antioxidant compounds consumed," she concluded.

This study was supported by the Netherlands Organization for Scientific Research and the U.S. National Institutes of Health. The authors have disclosed no relevant financial relationships.

Neurology 2013;80:904-910. Abstract