Heather Shilling has been taking hormones for the past four decades. She is in her 60s now, and a great Hormone Replacement Therapy (HRT) enthusiast. She took the contraceptive pill through most of her fertile years, pausing only to have three kids. And because she didn't smoke and was generally healthy, her doctor at the time carried on prescribing the pill right up to her menopause, when she switched to HRT. "Sometimes I do stop and wonder what 40 years of taking hormones will have done to my body," she says. "But two of my close friends have had breast cancer and another has just had a heart at tack, whereas I'm the fittest of the lot of us."

Eighty-five million pill takers worldwide will be as relieved as Shilling to hear that the latest news on the pill is that it protects women from heart disease and stroke, as well as from cancer of the ovary and womb (endometrium). And any lingering worries about whether it increases the risk of other cancers is dispelled by another new study of American women in whom pill use didn't increase the risk of either breast or cervical cancer.

These results were presented at the American Society of Reproductive Medicine conference in Philadelphia last week by the aptly named Dr Rahi Victory. He won the conference prize for the most important piece of research presented to the meeting. The data comes from the ongoing Women's Health Initiative (WHI) study which is tracking a group of more than 160,000 women. Some 41% of women in the study had taken the pill, and they have subsequently had a 17%-50% reduction in their risk of having a stroke or heart attack. Women like Shilling, who had taken the pill for many years, had the lowest risk. And the overall risk of getting cancer was also reduced by 7%-13% among pill users, with a clear reduction in ovarian and endometrial cancers and no effect on breast and cervical cancers.

Good news for Shilling and the 3.5 million pill users in the UK. But have we really heard the last on this? The WHI study, has previously reported data linking HRT to an increased risk of breast cancer, heart disease and strokes. And the contraceptive pill and HRT are practically the same; both containing the female sex hormones oestrogen and progestogen. It's true that the proportions, doses and chemical structure of both hormones differ between preparations, but essentially they've got the same ingredients. So how can the pill be so great for you, and HRT be so bad?

For every woman like Shilling who feels that taking hormones has been a safe and beneficial thing to do, there will be another who is instinctively wary. Hormone enthusiasts argue that the pill and HRT are only synthetic versions of the chemicals that our ovaries produce naturally. If you're not on the pill, there's a monthly ebb and flow of hormones to stimulate the ovaries, to build up the womb lining, to shed the lining if the egg isn't fertilised, and then to start the whole business over again.

The chemicals that we call hormones have a particular job to do, and they travel round the body in the bloodstream until, like a key fitting into a lock, they reach their destination. In other words, they have no effect in most parts of the body they pass through, but can have just the right effect at their destination. Taking hormones artificially overrides all that. When you take the contraceptive pill, you get a constant dose of oestrogen and progestogen for three out of four weeks. This fools the brain into thinking that there's no need to pump out hormones to tell the ovaries to ovulate. So you don't. And without ovulation, you can't get pregnant. And what data such as the WHI results seems to suggest is that the constant levels of hormones in the pill may be better for you than the ups and downs of natural hormonal fluxes.

But we are a nation of sceptics. And although we have wholeheartedly embraced the pill, it's probably because the fear of pregnancy is even stronger than our mistrust of hormones. When it comes to taking HRT, British women vote with their feet - the vast majority never take it, and most of those who do give up within the first year.

Pill expert Dr Anne Szarewski works as a clinical consultant at Cancer Research UK and is a leading family-planning doctor at the Margaret Pyke Centre in London. She has prescribed the pill to countless women, and is delighted at its latest clean bill of health. But she warns against unbridled enthusiasm that paints the pill as the elixir of life.

"These research findings were presented at a conference but have yet to be published in a journal," she warns. "I certainly hope that the claims are true, but it isn't really possible that the pill is as protective as they are saying."

Szarewski says that perhaps the women who take the pill are healthier than non-pill takers to start with, and that is why they go on to develop fewer heart attacks and strokes. Doctors don't usually prescribe the pill to women who are diabetic, obese or to smokers over 35. So young women who take the pill tend to be those with the lowest risk of heart disease anyway. This study hasn't proved that it's taking the pill that protects them: and the fact that the pill doesn't increase the risk of breast cancer may be because women who are most likely to get breast cancer, because it runs in their family, are avoiding it.

But Szarewski does concede that the pill definitely seems to protect women against cancer of the ovary and endometrium. And she says that the jury is still out about whether the pill increases the risk of cancer of the cervix. "No one knows whether the slightly increased risk of cervical cancer that has been noted in the past is due to the pill itself or because pill users are likely to sleep with more men and are less likely to use condoms than non-pill users," she says. She suspects that the risk of cervical cancer has more to do with how many men you sleep with than the method of contraception.

But despite her caution about the WHI results, Szarewski says that the known benefits of the pill are numerous. "We know the pill reduces ovarian and endometrial cancer, heavy and painful periods, pelvic inflammatory disease, and helps conditions like rheumatoid arthritis. On balance, I'm sure the pill is beneficial," she says.

But what of the pill's close relative, HRT? How does she explain the fact that while the pill is obviously a good thing for most, the reputation of HRT is slithering downwards?

"There really is no good evidence that HRT is beneficial [in preventing cardiovascular disease]," says Szarewski. "But as it is given to older women, we expect to see more health problems. The population of young women that takes the pill is generally fit and well. Even if the pill did cause a small increase in risk of heart disease or stroke, you still wouldn't see significant numbers because the overall risk is so tiny. But among HRT users, the overall risk is much higher and any increase among HRT users would be more apparent."

But why should the pill have no effect on your risk of developing breast cancer whereas taking HRT appears to increase the risk? Szarewski thinks that it might be that the seeds of breast cancer are usually sewn before you reach the menopause, though it may not become apparent for many years to come. Once you get to the menopause, your body stops producing oestrogen, and the chances of laying down the seeds of breast cancer fall. But if you take HRT, your body is still getting hormones that would otherwise have fallen drastically. So your risk of breast cancer remains as high as before the menopause.

HRT users can, though, take heart from a new US study also presented last week at the Philadelphia conference. The study pooled the results of 30 trials and represented 26,608 women. Being on HRT didn't increase death rates among women over 60 (though they may still be more likely to develop breast cancer). And HRT use reduced death rates in women under 60 by 39%. This may mean that HRT can be protective for women in their 50s or it may reflect the fact that women who take HRT tend to be healthier to start with. Either way, nice to know it won't kill you.

There was more good news for women who've taken hormones as part of fertility treatment. Until now, the suspicion has been that IVF treatment increases the risk of breast cancer - but a review of studies involving 50,000 women found no evidence that the hormonal drugs given as part of the treatment could either trigger breast tumours or worsen ones that were already there. Even better, when IVF works and a woman conceives, the procedure appears to reduce her chances of developing breast cancer by 26%, scientists found.

We haven't heard the last on links between hormones and cancer, but for women such as Heather Shilling there was plenty of reassurance coming out of Philadelphia last week.