British researchers revealed Thursday that birth control pill could protect women against ovarian cancer for 30 years or longer after they stop taking them.

Birth control pills have prevented 100,000 ovarian cancer deaths worldwide so far, and 200,000 women from developing cancer of the ovary, the researchers led by Valerie Beral, head of the Cancer Research UK epidemiology unit at University of Oxford wrote in the journal Lancet.

The new study is the first to discover the benefits of the pill when it comes to ovarian cancer.

“When you are 60 it matters whether you took it for five years or 10 years in your twenties. The longer you took it, the better off you are when the risk of ovarian cancer is high,” Beral said in a telephone interview with Reuters.

The findings result from the analysis of 45 studies on ovarian cancer in 21 countries and show that the benefits of the contraceptive pill outweigh the risks.

“The eventual reduction in ovarian cancer is bigger than any increase in other types of cancer caused by the pill,” the researcher said.

The study shows that 10 years of taking the pill reduced the incidence of ovarian cancer before age 75 from 12 cases per 1,000 women to eight. Those who take it for 15 years cut their risk by half. Death were cut from seven women per 1,000 to five.

What is the most significant finding of the research is that protection lasted for more than 30 years after pill use was stopped. This is important, as ovarian cancer is commoner in older women who have passed the menopause.

“More than 100 million women are now taking the pill, so the number of ovarian cancers prevented will rise over the next few decades to about 30,000 per year,” the study said.

Over the time, the contraceptive pills were thought to be harmful because they increase the risk of blood clots. However, a study of the pill dated on last September, spanning 36 years and run by the Royal College of General Practitioners, showed that it reduced the risk of three cancers - ovarian, womb and bowel in women who took it for up to eight years.

“Young women don’t have to worry about cancer from taking the pill because the eventual reduction in ovarian cancer is bigger than any increase in other types of cancer caused by the pill,” Sir Richard Peto, professor of epidemiology at Oxford University said.

Two Canadian researchers explained in a commentary for the Lancet that the protection offered by the contraceptive pills “stems from the cumulative suppression of ovulatory cycles.” Therefore, oral contraceptives “could help to decrease the number of cells that are likely to become malignant over a lifetime, whereas HRT after menopause could have a carcinogenic effect,” Eduardo Franco and Eliane Duarte-Franco from McGill University and the Institut National de Sante Publique du Quebec said.

Following this research, experts called for better access to oral contraceptives, arguing that the drugs should now be available over the counter.

According to the International Agency for Research on Cancer, there are more than 190,000 new cases of ovarian cancer a year worldwide.