The oral contraceptives used by more than 100 million women worldwide are coming under increasing fire.
Earlier this week, a Belgian study found that the pill causes artery-clogging plaque, which increases the risk of heart disease. And Thursday a study published in the British journal Lancet reiterates the link between the pill and cervical cancer.
If there's any good news for those taking oral contraceptives, it's that the new research suggests a higher risk of cervical cancer is reversible in the long term after women go off the pill.
"We already knew that the risk of cervical cancer increases in women taking the pill," says study author Jane Green. "What we didn't know is what happens after you stop taking it. We found that the risks start to fall, and by 10 years, the risk has dropped to normal levels."
Green, an epidemiologist at the University of Oxford, and her colleagues reported that women who take the pill for five years or more are twice as likely to develop cervical cancer as those who do not.
However, some doctors question whether there is a direct link between cervical cancer and oral contraceptives. This is because cervical cancer is caused by a sexually transmitted virus called the human papillomavirus, or HPV, and some experts believe the message of this study may be misleading.
"I fear that this paper, well intentioned as it is, will convey the wrong message to the public," says Dr. Diane Harper, a professor of women's and gender studies at Dartmouth College in Hanover, N.H. "The message that would be wrong for people to conclude is that prolonged use of oral contraceptives causes cervical cancer -- only HPV causes cervical cancer."
Rather, some doctors say the link between the pill and cancer may be due to increased sexual activity. They note women who are on the pill may be more sexually active, and therefore more likely to be infected with HPV.
"Does the pill increase risk of cervical cancer, or is it just that women who are on the pill tend to have more sexual relationships and more opportunities to get HPV?" asks Dr. Donna Shoupe, a professor of obstetrics and gynecology at the University of Southern California in Los Angeles.
Dr. Michael Bookman, vice president of ambulatory care and clinical research at Fox Chase Cancer Center, has the same concerns. "Just because they show an increase risk of cervical cancer in women taking the pill does not mean there is a direct relationship," he says.
"For example, women using the pill are more likely to have a greater number of sexual partners and to have sexual activity at an earlier age -- both of which lead to an increased likelihood of exposure to the virus."
In addition, women who take birth control pills may be less likely to use condoms, which means that they are not protected from HPV infection.
"We know that cervical cancer is caused by the HPV virus, and we also know that the transmission of HPV is reduced with condom use," says Dr. Lisa Jones, a gynecologist at the New Bedford Community Health Center in Massachusetts. "The important variable is the lack of condoms, not the presence of birth control pills."
The connection between the birth control pill and cervical cancer may be more complicated, however.