TOKYO (AFP) - Researchers in Japan say black tea could help treat osteoporosis, a bone condition affecting older people, but admit you need to drink an awful lot of it.

Scientists say the humble brew contains an antioxidant that can prevent the loss of bone density commonly seen in old age that makes the elderly more vulnerable to fractures.

The news is the latest claim for a drink that is a staple of countries around the world, and one over which never-ending arguments rage about how to brew the perfect cup.

Researchers led by Keizo Nishikawa of Osaka University found that theaflavin-3 (TF-3), the antioxidant, works by inhibiting the function of an enzyme called DNA methyltransferase, which destroys bone tissue.

The research, published in the online edition of the US journal Nature Medicine on Monday, found that mice suffering from osteoporosis who were given TF-3 showed recovering levels of bone volume, similar to those of healthy mice.

But it might be a bit early to rush to put the kettle on - the research found that a 60 kilogramme adult would have to drink 60 cups of tea over three days to see a noticeable difference, Jiji Press reported.

Osteoporosis particularly affects women in later life and is a growing problem in rapidly ageing societies such as Japan.