Published online 9 November 2007 | Nature | doi:10.1038/news.2007.234

News: Briefing

Contraceptive risks

Two studies out this week warn about possible long-term health consequences of taking birth-control pills. But does that mean the pill is dangerous? Heidi Ledford takes a look at why it’s so hard to get a straight answer.

So what are they saying about the pill?

Researchers have found that plaque accumulation in the arteries is greater in women who use birth-control pills than in those who never have. Plaque is the hardened fat and cholesterol that can clog arteries and lead to heart disease and stroke.

Pill popping: does one a day create health risks?Punchstock

Researchers at Ghent University in Belgium studied more than 1,000 women who had taken oral contraceptives for a period of time and then stopped. They found a 20-30% increase in the amount of plaque for every decade the woman was on the pill. The results were presented this week at the American Heart Association meeting in Orlando, Florida, but have not yet been published.

Meanwhile, another study published this week in The Lancet confirms previous findings that the risk of cervical cancer is higher in women who are on the pill1. That risk drops back down to normal levels within ten years of quitting the pill, they found.

Does this mean women on the pill should panic?

No. The overall risk of cervical cancer associated with birth control is nothing new. And although the findings on artery-clogging plaque are novel, they are also preliminary, cautions Sharonne Hayes, director of the Women’s Heart Clinic at the Mayo Clinic in Rochester, Minnesota.

“We know that when you are taking oral contraceptives there is an increased cardiovascular risk,” says Hayes. But several previous studies have shown that the risk declines after women stop taking the pill, she adds. Furthermore, the women in the plaque study had taken an older generation of birth control pills that contained higher doses of hormones.

“It’s an interesting finding and we should look more at this,” says Hayes. “But we shouldn’t read too much into it.”

If the cervical cancer findings aren't new, what else do we know about the birth-control pill and health risks?

Studies have shown that the pill can increase the risk of stroke, cervical cancer, cardiovascular disease and breast cancer. But other studies have also shown that it protects against ovarian cancer, endometrial cancer, acne ... and breast cancer.

Wait, why is breast cancer on both of those lists?

The jury is still out on breast cancer. This disease is known to be linked to hormone levels, so it makes sense to look for a link to the pill. An analysis of more than 150,000 women worldwide found a slightly increased incidence of breast cancer in women on the pill2. But other studies have found no effect of oral contraceptives on breast-cancer risk. And a study published last month found that use of the pill did not affect the likelihood of death from breast cancer in more than 4,000 women diagnosed with the disease3.

Different birth-control pills contain different amounts of different hormones; some pill formulations may actually reduce the risk of breast cancer, says Hayes.

How do other risks and benefits stack up against each other?

“It’s very, very hard to give an overall 'the pill is good, the pill is bad' assessment”

Jane Green
Cancer epidemiologist

A recent study of around 46,000 women found a slight reduction in total cancer risk in women who used birth control (the reduced risk of ovarian and endometrial cancer is generally thought to outweigh the increased risk of cervical cancer and breast cancer)4. But most of the women in that study were white and from the United Kingdom; the results may not hold true in other populations in other parts of the world. Some risk factors, such as how many children a woman has and how old she is when she has them, vary between women and between cultures.

"If using the pill allowed you to have fewer children and have the first child later in life, that alone would reduce the risk of cervical cancer," says Jane Green, a cancer epidemiologist at the University of Oxford, UK, and an author on the recent cervical-cancer study.

The risk of stroke during a full pregnancy and the post-partum period is twice as high as the risk from birth control, Green adds.

Can someone please just tell me if the pill is good or bad?

“It’s very, very hard to give an overall 'the pill is good, the pill is bad' assessment,” says Green.

Why is it so hard to get a straight answer?

In addition to differences between populations of women, study results can be muddied by differences in the composition and concentration of hormones in the many different birth-control pills on the market, says Hayes. “You can’t lump all oral contraceptives together.”

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Many studies were begun years or decades ago, when birth-control pills contained higher overall levels of hormones and the hormones were derived from different sources. “The drugs we’re using now are very different,” says Hayes.

“This is one of the problems we often face in medicine. We start a study only to have the treatment evolve radically between the beginning of the study and its end. You can get good results, but they’re not necessarily clinically relevant.”

And, Hayes notes, study designs are often less than ideal. “It would be very hard to randomize an oral-contraceptive trial,” she says. 

  • References

    1. International Collaboration of Epidemiological Studies of Cervical Cancer. Lancet 370, 1609-1621 (2007).
    2. Collaborative Group on Hormonal Factors in Breast Cancer. Lancet 347, 1713-1727 (1996). | Article | PubMed | ISI |
    3. Wingo P. A. et al. Obstetrics & Gynecology 110, 793-800 (2007).
    4. Hannaford, P. C. et al. Br. Med. J. doi:10.1136/bmj.39289.649410.55 (2007).
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