Taking vitamin E could increase the risk of a particular type of stroke, experts said.
A review found the vitamin increased the risk of suffering a haemorrhagic stroke (where bleeding occurs in the brain) by 22pc 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.
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 10pc.
This type of stroke, ischaemic, accounts for 70pc 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.
Today's 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.
The authors concluded: "Given the relatively small risk reduction of ischaemic stroke and the generally more severe outcome of haemorrhagic stroke, indiscriminate widespread use of vitamin E should be cautioned against."