A diet rich in antioxidants may not reduce the risk of stroke or dementia as hoped, a new study suggests.

It's thought that antioxidants may help protect against stroke by neutralizing damaging molecules called free radicals that are linked to heart disease and stroke.

Most of the difference in antioxidant levels in the studywas from differences in how much coffee and tea people drank. (David Gray/Reuters)

A previous analysis of the Rotterdam Study of aging of nearly 5,400 participants aged 55 and older when the study began suggested that higher intakes of vitamin C might be related to lower risk of stroke and vitamin E may be associated with reduced risk of dementia.

In Wednesday's issue of the journal Neurology, Elizabeth Devore of Harvard Medical School in Boston and her co-authors confirmed those vitamin results but no benefits or risks were found for total dietary antioxidants.

"Overall, we found little association between total antioxidant capacity in the diet, measured by FRAP, and major neurologic diseases of the elderly," they concluded.

FRAP or ferric-reducing antioxidant power evaluates antioxidants in the diet including flavonoids missed by other measurements, although the researchers said it doesn't include as much information as individual antioxidants assessments.

Over the study's average follow-up of 13.8 years, 599 cases of dementia were identified as were 601 cases of stroke.

The statistical model controlled for factors such as age, education, total calorie intake, smoking, body mass index and use of supplements.

About 90 per cent of the difference in antioxidant levels in the study was from differences in how much coffee and tea people drank. The beverages are high in flavanoids.

Participants filled in a meal-based checklist of foods and then a detailed food questionnaire during a clinical exam.

The researchers said their findings were consistent with the findings of the Nurses' Health Study in the U.S.

Another study of Italians with an average age of 50 found higher antioxidants levels in the diet were associated with reduced risk of ischemic stroke, although those in the Italian study got relatively more antioxidants from alcoholic beverages, fruits and vegetables rather than coffee and tea. "Growing epidemiologic evidence does suggest that higher consumption of fruits, vegetables and alcohol may be associated with reduced risk of stroke," Devore's team said. The study was funded by the Netherlands Organization for Scientific Research and the U.S. National Institutes of Health.