Vitamin E supplements may interfere with the process that keeps bones healthy, suggest Japanese scientists.
Writing in the journal Nature Medicine, the Keio University team said mice given large doses had lower bone mass - if the same was true in humans, fracture risk would be increased.
Vitamin E is found in oils, green vegetables such as spinach and broccoli and in almonds and hazelnuts.
But a UK expert said supplements could be problematic.
The relationship between nutrients such as vitamin D and bone health are well established, but there is far less research which looks at the role of vitamin E.
The research at Keio University in Tokyo looked at what happened when mice had not enough vitamin E, and what happened when they were given supplements.
Although some early studies suggested that consumption of the vitamin had a positive effect on bone mass, the Japanese team found the reverse was true, with bone health improving in the deficient mice, and losing bone mass when given supplements.
The size and density of bones in the body is not fixed in adulthood, but dependent on a balance between cells which lay down new bone, called osteoblasts, and cells which strip it away, called osteoclasts.
The researchers suggested that vitamin E could encourage the formation of osteoclast cells, which meant more bone was lost than would be laid down.
Similar experiments in rats, including work published in 2010, found the opposite results to the latest study, even suggesting that vitamin E could be useful as a bone-growth promoting treatment for older people.
But Dr Helen Macdonald, who researches the influence of nutrition on bone health at Aberdeen University, said that there were a small number of studies, including her own, which found negative effects.
She stressed there was no reason for people to change their diet to avoid the relatively small amounts of vitamin E contained in it.
She said: "However, vitamin E supplements involve doses far higher than those in a normal diet.
"There is increasing evidence that taking supplements doesn't do any good, and if anything, may be doing harm."