A simple cup of coffee may effect the estrogen levels in women in different ways.

Researchers found the amount of caffeine in just two shots of espresso or one large coffee a day changed the estrogen levels in young women.

The women drank caffeine from tea, coffee or soda. Asians had a significant increase in estrogen. Black women also had an increase.
Including breast and ovarian cancer, and osteoporosis.

But scientists said at the moderate caffeine levels studied no short term health effects.

For Caucasian women caffeine actually lowered estrogen. Researchers said they could not comment on long term health effect.
Studies in lab animals have shown estrogen variation reduces ovulation, causing difficulty conceiving.