Forty-something years ago women in the industrialised countries began taking the contraceptive pill en masse. Somebody thought they should have fewer children and wanted to make it easy for them. Of course, the easy way to achieve a goal is not always the safest way, and swallowing extra hormones month after month and year after year when there is nothing actually wrong with you seems like asking for trouble. Right from the beginning, then, health authorities acknowledged the need to monitor the safety of the pill, as well as its effectiveness.

In Britain, between 1968 and 1969, almost 46,000 women were enrolled in the Royal College of General Practitioners' oral contraception study -- 23,000 of whom were using the pill while the other 23,000 had never used it. They have been followed up ever since, minus the one third who have dropped out. The most recent account of their collective fate was published last week in the British Medical Journal and reported around the world under such headings as "Taking the Pill cuts the risk of cancer" and "The pill: new evidence shows it helps protect against cancer".  

One could just about hear the champagne corks popping in the head offices of the pill manufacturers who helped fund the study. Although oral contraceptives have been modified over the years to reduce side effects, bad news keeps surfacing. They have been linked with blood clots, strokes, heart attacks and diabetes. They increase a woman's risk of cancer of the breast, cervix and liver. Hormone replacement therapy for menopausal women is proving just as risky. In 2005 the World Health Organisation classified both OCs and HRT as group 1 carcinogens.

The whole idea of excess hormones being "good for you",
counter-intuitive as it is, may be due to missing data and historical
factors that no longer apply.

Negative findings, however, are regularly contested by studies which find the opposite, or explain away the side effects or defend them as risks that should be balanced against the benefits of the pill and managed so as to minimise the harm. The increased risk of cervical cancer, for example, is taken care of by screening programmes to detect early signs. The risk of breast cancer is only raised if a woman takes the pill for more than eight years, and so on.

There are even studies that show the pill is good for a woman's health. It appears to reduce the risk of cancer of the endometrium (lining of the womb), ovaries and possibly the bowel.

But a pill that is merely a mixed bag of risks and benefits is not particularly attractive to women and nor is it necessarily a sound public investment. What if it happens to be doing more harm than good on the whole? Should governments be shelling out vast sums of money to provide the pill for the deserving poor if it is going to increase the country's cancer burden?

On the other hand, if it can be shown to do more good than harm, or just break even, the pill stays in business.

Professor Philip Hannaford of the University of Aberdeen and his colleagues seem to have settled the question with their analysis of 36 years of data from the 1968 contraception cohort study. In that group of women, now at an age when the risks are growing, taking the pill did not increase the risk of cancer. Rather, it reduced the risk of cancer by as much as 12 per cent for those who had used it compared with those who had not.

Now, a 12 per cent reduction in cancer risk by the time one is 60ish is not a bonus that would make the average woman break out the champagne, although older women may be "reassured" as the study authors suggest.

But it is a significant figure to those dealing in the grand generalisations of public health. It means, says Prof Hannaford, one fewer cancer case for every 2,200 women taking the pill. Since there are about 3.5 million British women taking the pill, that would mean about 1590 fewer women with cancer in their lifetime -- a "net public health gain", as the authors note.

Even that much gain, however, is uncertain. By 2004 one third of the women had dropped out of the study and data for the remaining women was not complete in every case. When the researchers did a separate analysis of those with complete data from their GPs up until 1996, the reduction in cancer risk dwindled to 3 per cent -- a statistically insignificant result.

Erring on the side of caution, therefore, the most that can be said in favour of the pill on the basis of this study is that cancer risk is not increased, on the whole, by using oral contraception. So much for headlines about "cutting" cancer risk.

In fact, the whole idea of excess hormones being "good for you", counter-intuitive as it is, may be due to missing data and historical factors that no longer apply.

Missing data: In an online letter Dr Ellen Grant, a long-time critic of the pill, points out that the study probably underestimates the role of HRT later in life among women who never used the contraceptive pill. She notes that the authors kept no records of HRT use since 1996, even though many menopausal women were using the therapy after that. This could boost the cancer rates of the non-pill-users and could account for the fact that the Aberdeen study, unlike many others recently, found no increased risk for breast cancer among pill users.

Historical factors: Those enrolled in the study in 1968 and 1969 were all married or living in a stable relationship (and most were white). Many would already have had a child before starting on contraception -- a factor which is known to reduce the risk of breast cancer in women taking the pill.

Also, they took the pill for an average of four years and the majority for not more than eight years -- the critical cut-off point for avoiding cancer, according to the authors.

Today's young women are in a very different situation, many of them 30 or more before they marry, which is when they are most likely to have their first child. In the meantime they are likely to have been through more than one sexual relationship and cohabited with at least one partner. Although these relationships do not preclude children they are less open to procreation and so increase the demand for contraception -- the pill being the most popular method.

And yet, if a young woman starts taking the pill at 18, which is not uncommon, what is she to do at the age of 26 when her eight "safe" years of hormonal contraception are up and marriage is still not on the horizon? Will she suddenly abstain from sex, or will she fall back on condoms, and abortion to compensate for their even higher failure rate?

Cancer is not the only serious risk of the pill. More deadly is the way it has changed the meaning of sex and eroded the chances of a happy and fruitful marriage. Throw that into the calculations and the net public health gain becomes a personal and social dead loss.

Commenting on the British study a London Times writer reaches the verdict that "the developers of the Pill did a good job. They helped to liberate a generation of women without doing them any harm." 

Tell that to the thirty-something men and women who are still looking for a spouse and hoping for children. Tell the girls their cancer risk might be down by 12 per cent. And see how grateful they are.

Carolyn Moynihan is Deputy Editor of MercatorNet.