Even newer lower-dose birth control pills raise a woman's risk of breast cancer, although the actual danger is "quite small," researchers reported Wednesday.
Hormone-infused devices such as vaginal rings, implants and some IUDs also appear to raise the risk, although again not by much, the study found.
It's a disappointment to doctors who had hoped that lower doses of hormones in both oral and non-pill contraceptives might be safer than older birth control pills. But they stress there is no need for most women to abandon birth control pills for fear of breast cancer.
"When we look at all comers, the absolute overall increased risk of breast was one extra case of breast cancer for every 7,690 women using hormonal contraception for one year," said Dr. Rebecca Starck, a gynecologist at the Cleveland Clinic, who was not involved in the study.
"It's really quite small — not to say it's zero. Yes, hormonal contraception may increase your risk for breast cancer, but the absolute risk of breast cancer is small."
This study was done in Denmark, where every resident is on a register of medical visits and drug purchases. The researchers tracked nearly 1.8 million women starting in 1995 and compared those who purchased birth control methods with women who developed breast cancer.
Overall, the use of any hormone-based contraceptive for five years or more raised a woman's risk of breast cancer by 20 percent, Lina Morch of the University of Copenhagen and colleagues reported in the New England Journal of Medicine.
The risk of breast cancer ranged from a 9 percent increase among women who used birth control for a year or less, to a 38 percent greater risk if a woman used it for 10 years or more.
Breast cancer is the second-biggest cancer killer of American women, after lung cancer. The American Cancer Society says every year it's diagnosed in 200,000 women and a few men, and kills around 40,000.
Other studies had shown about the same breast cancer risk for older versions of birth control pills.
"There were hopes that the new formulations would not increase a user's risk of breast cancer as the older formulations did," said Mia Gaudet, strategic director of breast and gynecologic cancer research at the American Cancer Society, who was not involved in the research.
"Yes, hormonal contraception may increase your risk for breast cancer, but the absolute risk of breast cancer is small."
"Unfortunately this was not the case and additional research is needed to tweak the formulation. In the meantime, women who are using oral contraceptives might want to speak to their doctors about use before age 35 and after age 35. Depending on their reasons for using oral contraceptives, they might want to consider other options, including non-hormonal contraceptives."
Some intrauterine devices (IUDs) do not employ hormones. Condoms and diaphragms do not deliver hormones.
"We always thought that non-oral hormonal contraception like the IUD is more of a localized form and systemically didn't affect women in the same way. But in the study it does appear that any form is basically the same," added Dr. Taraneh Shirazian of New York University's Langone Joan H. Tisch Center for Women's Health.
However, hormonal birth control does lower the risk of other cancers, including ovarian cancer and endometrial cancer, and it may lower the risk of colon cancer.
Most breast cancers are fueled by estrogen. Over the years, makers of birth control pills and hormone replacement therapy for women past menopause have reduced the amount of estrogen in their products.
Two types of birth control pills are sold in the U.S. — one that combines synthetic versions of the hormones estrogen and progesterone, and the "minipill" that only delivers progestin, a synthetic formulation of progesterone.
Shirazian notes that for women of average risk of breast cancer, the concern is not high.
"The relative risk increase in this study is only 1.2 on average. That is not a huge risk increase," she told NBC News.
"That is a very small extra risk. Don't forget there is relative risk of death in pregnancy, too. The risk of dying when you're pregnant is probably higher."
The National Cancer Institute estimates that 12.4 percent of women born in the United States will develop breast cancer at some time during their lives. That roughly translates to a 12 percent lifetime risk for a woman, although many factors affect breast cancer risk.
They include smoking, obesity, starting menstruation early, having children late in life or not at all and not breastfeeding. Any woman's risk of breast cancer goes up as she gets older.
"No one should take (oral contraceptives) without careful thought, but the advantages in avoiding an unwanted pregnancy will usually more than outweigh the very slightly increased risk of breast cancer," said Ashley Grossman, emeritus professor of endocrinologyat Britain's University of Oxford.
"And there is also the reassuring thought that oral contraceptive use may decrease the risk of ovarian and endometrial cancer."