Women who use contraceptive pills with high doses of estrogen are at 50 percent risk of developing breast cancer, a new research shows.

For the research, the study authors examined 1,102 women diagnosed with breast cancer and 21,952 controls. All the participants were a part of the Group Health Cooperative in the Seattle-Puget Sound area and received a cancer diagnosis between 1990 and 2009.

Researchers used electronic pharmacy records to get detailed information on oral contraceptive use including drug name, dosage, and duration of medication.

Researchers found that women who consumed birth control pills had 50 percent increased risk of breast cancer. The team found that birth control pills that had high-doses of estrogen increased breast cancer risk 2.7-fold and the pills containing moderate-dose estrogen increased the risk by 1.6-fold. Contraceptive pills with ethynodiol diacetate raised the risk 2.6-fold and triphasic combination pills containing an average of 0.75 milligrams of norethindrone amplified the risk 3.1-fold.

"Our results suggest that use of contemporary oral contraceptives (birth control pills) in the past year is associated with an increased breast cancer risk relative to never or former oral contraceptive use, and that this risk may vary by oral contraceptive formulation," said Elisabeth F. Beaber, PhD, MPH, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington, in a press release.

Beaber said that the study results should be interpreted carefully. Previous researchers showed the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives.

A recent study on breast cancer showed that night light exposure makes the commonly prescribed drug tamoxifen resistant to the treatment. Researchers explained that melatonin, essential for success of tamoxifen, shuts down due to light exposure at night.

The findings of the current study were published in Cancer Research, a journal of the American Association for Cancer Research.