More than a cup of coffee a day may alter estrogen levels in women.

What's more, the effects may change depending a woman's race.

Asian women who drank an average of two cups of coffee a day had higher estrogen levels than those who drank less. The opposite was found among white women whose estrogen levels were lower than those who drank less.

There seems to be no significant impact at least in the short-term, but researchers say more studies are needed.

This study included various caffeine sources -- coffee, soda and tea.