Osteoporosis is a serial killer. It affects one in three women and one in 12 men - and kills more women than all gynaecological cancers put together. Bones get progressively more brittle until they snap and when they do, it's bad news. One in six women taken to hospital with a hip fracture, will not come out alive and men fare even worse. But for some reason, we're not engaging with it as a serious problem: this week a survey found breathtaking ignorance amongst women about the disease.

Unlike cancer, it is actually fairly easy to predict who is likely to get osteoporosis. "At least 30% of the cause of osteoporosis is genetic," says expert Dr Gordana Prelevic. "Any woman with a mum, grandmother or aunt who had a hip fracture is at greatly increased risk. We also know that women who don't have periods for long stretches of time because of anorexia, or because they breastfeed for a long time or go in to an early menopause, are at risk. Heavy smokers and very underweight women are also more prone."

The chances of walking into a GP surgery and being offered unsolicited advice about preventing osteoporosis are extremely slim if you are a woman and next to nothing if you're a man. Finding out whether you have osteoporosis can also be tricky. Bone-density scanning, which is only available in some areas, can provide useful information.

But the measurements are but one part in the complex mosaic of osteoporosis, which is really about fragile bones. Some women will have terrible bone density scans, but will never fracture a bone or get any pain, while others have reasonable bone density scans and have one fracture after another. "If you know you are at risk of osteoporosis, because of your family history or because you have two or more of the other risk factors, you should take precautions against osteoporosis, regardless of whether or not you can get a bone density scan," warns Dr Prelevic.

She is scathing about self-testing kits available in pharmacies throughout the land. "They're rubbish! My local pharmacist in Hampstead was very apologetic to me for selling them, but she told me that people do ask for them, which is a shame because they can give people a false sense of security or cause unnecessary panic."

So how do you guard against the disease in the future? Bones need calcium and vitamin D to keep them strong. There's a lot of emphasis on eating calcium rich foods such as milk, cheese and sardines to prevent osteoporosis, but vitamin D, which comes from animal fats in our diet and which we can also make ourselves when exposed to sunlight, may be the missing factor for many of us. "Every other person that I see in my clinic in central London seems to be vitamin D deficient whereas most are eating enough calcium. We tend to associate vitamin D deficiency with Asian women who don't get much sunshine and eat vegan diets, but I see lots of non vegan Caucasians who need extra vitamin D too because our Northern hemisphere sunshine is too weak to be useful," says Dr Prelevic.

The recommendation is that women under 65 who eat a well balanced diet are probably getting the right amount of calcium, namely 1000-1500mgs a day. Unless your diet is very low in calcium, that is less than 400mgs a day, you are unlikely to benefit much from calcium supplements. After the age of 65, taking a calcium supplement which includes vitamin D is wise, however good your diet. A little bit of vitamin D, contained in cod liver oil capsules, would do us all good, apparently. Regular exercise makes a big difference; it keeps bones strong and older people who keep exercising fall over less and are less prone to fractures. A glass of red wine a day's good for bones, but getting legless isn't.

There is no perfect treatment for established osteoporosis. Dr Prelevic tends to suggest HRT for women in their 50s who have menopausal symptoms such as hot flushes and early osteoporosis. For women who can't take HRT or don't want to, older women or men with severe osteoporosis, she prescribes alendronate (Fosamax), which causes stomach inflammation in up to a fifth of users, but can now happily be taken just once a week. This drug prevents destruction of bone, but only tiny amounts of it are actually absorbed and taking it with indigestion tablets can render it totally ineffective.

Osteoporosis remains a worrying health problem that is just as likely to affect us as cancer is. If only cancer could be prevented by cod liver oil, a glass of wine, a walk round the park and a snooze in the sunshine, we'd all sleep easier tonight.