Taking vitamin E could increase the risk of a particular type of stroke, experts have said.
A review found the vitamin increased the risk of suffering a haemorrhagic stroke (where bleeding occurs in the brain) by 22% compared to people not taking it.
The overall risk was small, accounting for one extra haemorrhagic stroke for every 1,250 people taking vitamin E.
Haemorrhagic strokes are the least common type and occur when a weakened blood vessel supplying the brain bursts and causes brain damage.
The review, from experts at Harvard Medical School in Boston in the US, also found vitamin E could actually cut the risk of the most common type of stroke by 10%. This type of stroke, ischaemic, accounts for 70% of all cases and happens when a blood clot prevents blood reaching the brain.
Experts found vitamin E could cut the risk, equivalent to one ischaemic stroke prevented per 476 people taking the vitamin. However, they warned that keeping to a healthy lifestyle and maintaining low blood pressure and low cholesterol have a far bigger effect on cutting the risk of ischaemic stroke than taking vitamin E.
More than 111,000 people have a stroke every year and they are the third biggest cause of death in the UK. Those who survive are frequently left with disability.
Dr Peter Coleman, deputy director of research at The Stroke Association, said: "This is a very interesting study that shows that the risk of haemorrhagic stroke can be slightly increased by high levels of orally taken vitamin E, although what is a 'high level' has not clearly been ascertained, and more research is required to discover the mechanism of action and the level at which vitamin E can become harmful.
"The Stroke Association urges people to maintain a lifestyle of a balanced diet, regular exercise and monitoring their blood pressure to reduce their risk of a stroke but would be very interested in seeing further research into this study."
The study, published online in the British Medical Journal (BMJ), included nine studies on almost 1.2 million people to investigate the link between vitamin E and stroke.