"Women who take oral contraceptives have a 50% higher risk of having lupus than women who don't take them," says study researcher Samy Suissa, PhD, a professor of epidemiology at McGill University in Montreal.
But to put that in perspective, he says the overall risk is still small. In the study, Suissa and colleagues also found the risk higher in women who take the higher dose pills -- those with 50 micrograms of estrogen or more -- and in women currently taking them who have just taken the pills for a few months.
The study is published in the April 15 issue of Arthritis & Rheumatism.
Oral Contraceptives and Lupus: Study Details
Previous studies focusing on a possible link between birth control pills and lupus have produced conflicting results, Suissa tells WebMD.
His study evaluated more than 1.7 million women, ages 18 to 45, who were in the U.K. General Practice Research Database, which includes more than 6 million people.
The women had prescriptions for combined oral contraceptives, which contain both the hormones estrogen and progestin. The researchers followed the women for eight years, on average, and found that 786 women had gotten a first-time diagnosis of lupus.
In lupus, something goes awry with the immune system, and the body produces autoantibodies that attack and destroy healthy tissue, according to the Lupus Foundation of America. Patients have inflammation, pain, and damage in various parts of the body.
Suissa's team matched up each patient with lupus to 10 people from the study database who did not have lupus when the patient was diagnosed.
They found use of oral contraceptives was linked with an increased risk of getting the disease. "I think we have clear evidence that these pills, especially at higher doses, can increase the risk of lupus," Suissa says.
But the contraceptive alone probably does not boost the risk, he says. "We think it probably interacts with some genetic predisposition."
Oral Contraceptives and Lupus: Study Statistics, Perspective
While the overall risk of birth control pill use and lupus was boosted by 50%, or 1.5 times, Suissa says, the risk went up by 2.5 times among new users, during the first three months.
He also found that the higher doses of pills -- those with 50 micrograms of estrogen or more -- was associated with a higher risk of lupus than the lowest dose -- those with 30 micrograms or less of estrogen.
Those who took the highest dose pills had a 2.9 times increased risk of lupus, while those who took the lowest had a 1.4 times higher risk, he says.
Even so, Suissa says, the overall risk of getting lupus is still small. "In the general population, lupus will appear in six people per 100,000 per year," he says. "If you say, 'OK, let's assume all these women are using the pill, this will go to nine," he says, referring to the finding of a 50% increased overall risk of lupus associated with pill use.
"The benefits of the pill are certainly very high," he says. "Compared to these risks [of lupus], our study makes it clear that with the newer pills, at the lower doses, that in essence this risk is almost nonexistent."
The study suggests that "the risk for oral contraceptives causing lupus is there but it's small," says Bevra Hahn, MD, chief of rheumatology and arthritis at the University of California Los Angeles David Geffen School of Medicine and a member of the medical-scientific advisory council for the Lupus Foundation. .
The finding about higher-dose pills boosting the risk of lupus more than low-dose pills is new, Hahn says. The take-home point? "The lower the estrogen content you can manage, the less likely [the pill] is to cause lupus in someone who doesn't have it," she says.
''There is no well-established link between combined oral contraceptive use and the development of lupus," says Rose Talarico, a spokeswoman for Bayer HealthCare Pharmaceuticals, based in Wayne, N.J. which makes two types of birth control pills.
But, she adds, the labeling for combined oral contraceptives does caution that persistent lupus can be made worse with use of the pills.
Many lower-dose options are available these days, she says. Bayer, for instance, makes Yaz and Yasmin; both have 30 micrograms or less of estrogen, she says.