The antioxidant content of fruits and vegetables may help mediate their protective effect against strokes caused by blood clots, US researchers claim.

The team, led by Dr Elizabeth Hak from Harvard School of Public Health in Boston, Massachusetts, found that men with high blood levels of carotenoids - antioxidants that are abundant in fruits and vegetables - were less likely to suffer a stroke than those with low levels.

Although a high intake of fruit and vegetables is known to have a beneficial effect on the risk of ischemic stroke, it was not known which specific nutrients conveyed this benefit, the researchers explain in the journal Stroke.

As part of the 13-year Physicians’ Health Study, the team analysed blood levels of five major carotenoids, as well as retinol (vitamin A) and tocopherol (vitamin E), among 297 male doctors with ischemic stroke, and 297 “healthy” individuals of the same age.

The researchers found that higher blood levels of the carotenoids a-carotene, ?-carotene, and lycopene were associated with a lower risk of ischemic stroke.

Further analysis revealed that men whose blood levels of the three carotenoids were in the lowest fifth of the study group had a 40% greater risk of ischemic stroke than those with higher levels. However, a similar risk of stroke was seen among all those with plasma levels of carotenoids greater than the lowest fifth.

No significant association with stroke risk was observed for the other antioxidants and vitamins studied.

“Our data suggest that higher plasma [blood] levels of carotenoids, as markers of fruit and vegetable intake, are inversely related to risk of ischemic stroke and provide support for recommendations to consume fruits and vegetables regularly,” the researchers conclude.