Sept. 11, 2007 -- More than 300 million women have used oral contraceptives since they were introduced in the early 1960s. Now a 36-year study shows a slight decrease in overall cancer risk in users of the pill.
In one of the largest and longest follow-up studies ever to examine the issue, researchers found a 12% decreased risk of any cancer in oral contraceptive users compared with women who never used birth control pills.
The study included 46,000 women followed for almost four decades from the late 1960s through 2004, when most were in their early to late 60s.
Researcher Philip Hannaford, MD, of the University of Aberdeen, says comprehensive cervical cancer screening, which is the norm today but was not in the early years of the study, can minimize this risk for long-term oral contraceptive users.
The findings appear in the latest online issue of the medical journal BMJ.
"The overall message is that women should not be frightened of the pill," Hannaford tells WebMD. "This is a very effective and safe method of contraception, especially when combined with regular cervical cancer screening."
The Pill and Cancer
Numerous studies over the years have examined the impact of oral contraceptives on cancer risk.
The consensus, based on the bulk of the research, is that contraceptive pill users have a slightly increased risk of breast, cervical, and liver cancer while they are on the pill and for a few years after.
Oral contraceptive users have also been found to have a lower risk for ovarian and uterine cancer, and that the protection lasts for at least 15 years after women stop taking oral contraception, Hannaford says.
The current study was done, he adds, to examine the overall pattern of cancer risk associated with oral contraceptive use.
The average age of the women in the study was 29 at recruitment between 1968 and 1969. Roughly half used oral contraceptives and the other half did not.
The women were followed for an average of 36 years, during which time the University of Aberdeen researchers recorded a 12% reduction in overall cancer risk, based on data from a large subset of the women derived from national cancer registries.
That translates to one fewer case of cancer for every 2,200 women who took the pill for a year, Hannaford tells WebMD.
Specifically, contraceptive pill users had significantly lower rates of colorectal, uterine, and ovarian cancer.
'Benefits Outweigh the Risks'
The researchers reported a 22% increase in overall cancer risk among women who took the pill for eight years or longer, including a 2.7-fold increase in cervical cancers and a fivefold increase in rare central nervous system and pituitary cancers.
They had no explanation for the increase in the latter cancers, but noted that the cervical cancer association has been well documented.
Most of the women in the study took the first generation of birth control pills, which contained much higher doses of hormones than are used in the oral contraceptives available today.
Hannaford says it is not clear if the risks and benefits are the same with the newer, lower-dose pills most women take today, but he suspects they are.
"I think these findings do have relevance for today's users, but I am pushing the boundaries a bit to say this because there isn't a lot of research," he says.
The researchers conclude that for most women who take birth control pills, "the cancer benefits associated with oral contraception outweigh the risks."
American Cancer Society epidemiologist Carmen Rodriquez, MD, does not disagree with the statement.
"We know that there is a small increase in breast cancer risk among women who take oral contraceptives, and this cannot be ignored," she says. "But we also know that oral contraception use lowers the risk of ovarian cancer. Since this cancer is so deadly and since we don't have good ways to screen for it or prevent it, I think it's fair to say that the benefits outweigh the risks."