Eating plenty of fruits, vegetables and whole grains that are rich in antioxidants may help reduce a woman's risk of stroke, even if she has a history of heart disease, 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.

"Eating antioxidant-rich foods may reduce your risk of stroke by inhibiting oxidative stress and inflammation," said study author Susanne Rautiainen, a doctoral student at the Karolinska Institute in Sweden.

For the study in this week's issue of Stroke: Journal of the American Heart Association, Rautiainen and her co-authors followed more than 31,000 women without cardiovascular disease and another 5,700 women with that history who filled in questionnaires about their diet and other lifestyle factors.

After more than 11 years, there were 1,322 strokes among women without a history of heart disease or stroke. Among women with previous heart disease or stroke, 1,007 strokes were recorded after about 10 years.

For those who ate the most antioxidant-rich foods and had no history of cardiovascular disease, the risk of stroke was 0.83 times that of those who ate the least, the researchers said.

Among those with a history of the disease, the risk of hemorrhagic or bleeding stroke was 0.10 times lower for the women had the highest levels of antioxidants in their diet compared with those eating the lowest amounts.

Fruits and vegetables contributed about half of the antioxidant capacity in women with no history of heart disease. Other contributors were:

- Whole grains (18 per cent).

- Tea (16 per cent).

- Chocolate (5 per cent.)

The protective effect remained after taking other factors into account such as exercise, smoking and education.

Researchers suspect that antioxidants may block atherosclerosis or hardening of the arteries through a variety of potential ways, such as lowering blood pressure and anti-inflammatory effects.

In contrast to these diet findings, randomized controlled trials of antioxidant supplements have failed to show beneficial effects of the pills on stroke risk, the study's authors said.

The study included detailed data on diet with a large number of stroke cases.

But the authors acknowledged that they only used dietary information from when the study started, and participants' blood pressure and cholesterol levels weren't measured at that time.

The study was funded by the Swedish Research Council for Infrastructure and the Swedish Council for Working Life and Social Research.