Japanese researchers have found that a substance in black tea may be effective for treating osteoporosis, a disease that causes bones to become weak and brittle.

The team, including Keizo Nishikawa, assistant professor at Osaka University, found that theaflavin-3, or TF-3, a substance in black tea, blocks an enzyme - DNA methyltransferase - that increases osteoclasts, cells that destroy bone tissues.

In a study published in the journal Nature Medicine, researchers said that after TF-3 was administered to mice suffering from osteoporosis, their bone volume recovered to levels similar to those of normal mice.

If the experimental conditions are applied to humans, however, a person weighing 60 kg would need to drink 60 cups of black tea every three days, 'The Japan Times' reported.

The discovery may pave the way for development of teas or supplement foods containing a large amount of TF-3.

However, Nishikawa said that products using TF-3 may have very bitter taste because it is a type of catechin, a bittering agent.