Women who begin hormone therapy at the start of menopause have a higher risk of developing breast cancer than women who start the therapy five or more years after menopause, a new study suggests.

Women who started estrogen-progestin hormone therapy five or more years after menopause had half the risk of developing breast cancer as women who started the same therapy as soon as they stopped getting monthly periods, said study researcher Valerie Beral, an epidemiology professor at the University of Oxford in England. The researchers followed up with the women for three years after they were first surveyed on their menopausal status and hormone therapy use.

"The risk was still there, but it was still quite a big effect," Beral told MyHealthNewsDaily.

Women who started estrogen-only hormone therapy at the start of menopause had a slight risk of developing breast cancer, but that risk also seemed to go away for women who started the therapy five or more years after menopause, the study said.

In the United States, hormone replacement therapy with estrogen and progestin is not recommended for long-term use because of cancer risks . But the new study suggests that it might be OK to take estrogen therapy, so long as you do it long after you start menopause, Beral said.

Beral and her colleagues looked at the health data of 1.13 million women who participated in the Million Women Study in the United Kingdom.

The results held true even if the women were overweight or obese, or used hormone therapy for short or long durations, the study said.

The findings mirror that of a previous Women's Health Initiative trial in the U.S., which also found that a lag time for starting hormone therapy decreased breast cancer risk, she said.

The study was published today (Jan. 28) in the Journal of the National Cancer Institute.

Pass it on: Starting hormone therapy five or more years after menopause decreases breast cancer risks, compared with starting directly after menopause begins.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.