The following correction was published in the Guardian's Corrections and Clarifications column, Friday December 14 2007

In the article below about osteoporosis we said that only people over 75 would be given a DXA bone scan on the NHS. We should have made clear that scans are available to anyone under that age who is considered by their GP to be at risk of developing osteoporosis. In the same piece we quoted a doctor who runs a private London clinic offering bone scans, but wrongly referred to her as a consultant. The second error has been corrected.

In terms of fright factor, osteoporosis is the new breast cancer. For a while now, women have been warned that their bone may be becoming progressively less dense and more fragile, until fractures are inevitable. The most severe cases can end up in wheelchairs.

But we only began to hear about it when the pharmaceutical industry launched drugs to treat it. Suddenly it was high-profile. Prince Charles's then fiancee Camilla Parker Bowles became president of the National Osteoporosis Society, and scanning machines to register bone density were proliferating in a variety of private clinics, funded by the drug manufacturers. Industry critics began to talk about osteoporosis as a prime example of "disease-mongering" - where drug companies talk up the condition to establish a market for their products.

If some of the steam has evaporated from the osteoporosis scare, it is because the government's rationing body, the National Institute for Health and Clinical Excellence (Nice) has ruled that osteoporosis drugs that help build up bone density should not be made available on the NHS to anybody below the age of 75, unless they have serious risk factors, such as a family history.

Osteoporosis is a desperate condition for 2 million women, more than a quarter of whom are over 80. So it is more than reasonable that younger women want to know whether they are at risk and, if so, how they can help keep their bones strong.

But the NHS will not send you for their gold-standard diagnostic test - a scan of your spine and hip using a special x-ray machine called a DXA (dual energy x-ray absorptiometry) - until you are 75 and your doctor thinks you could be at real risk of breaking your bones. If you are 50 and looking for reassurance about the state of your skeleton on the basis that prevention must be better than cure, you won't get a scan on the NHS. So you are quite likely to end up paying for a test at a private clinic, which uses a much cheaper device that will scan your heel bones using ultrasound.

"Generally it should be in the same ball park, but it is a different sort of technology," says David Reid, professor of rheumatology at Aberdeen University and chair of the National Osteoporosis medical board.

In fact, the DXA scans, measuring hip and spine density, are the only reliable predictors of who will benefit from the drugs - not least because they are the machines used in the drug trials.

Richard Eastell, professor of bone metabolism at Sheffield University, says ultrasound is not bad at predicting fractures, but should only be used to give a general idea of osteoporosis risk. If a woman has a bad score on the heel machine, she needs to be referred to a hospital with a DXA.

Arguably a private ultrasound scan for most younger women is a waste of time, because if you were high risk - and you can't have osteoporosis drugs unless you are high risk - your GP should be able to spot it. So you'd be better off strengthening your bones by improving your lifestyle with plenty of exercise and a healthy diet.

But private clinics such as the one that Walker went to claim there is a rationale for their tests. Those who have a bad score are recommended to take nutritional supplements, as well as exercise, which they insist can make a real difference.

The doctor who runs the clinic visited by Walker says her ultrasound machine is comparable to a DXA. "The ultrasound we use is a Sahara machine which is made by the same people who make DXA," she says. "With anything, you can sometimes get a misreading. It is very unusual but it is not unknown. The machines are fine, but even the DXAs have been known to give false readings. It could have been the DXA in Ms Walker's case."

She denies that Walker could have been told not to go for a DXA scan by her clinic. "That would not have been the case. She would have been told the DXA was the gold standard."

She insists the supplements she recommends will help women with the beginnings of osteoporosis - a condition called osteopenia. "You can make a world of difference," she says. "You have to have the right hormone balance and you have to have the right supplements." Most important, she says, is to have the right balance of calcium and magnesium.

But the National Osteoporosis Society does not recommend supplements. "If we eat a healthy, balanced diet then we should be able to get all the necessary vitamins and minerals to build and maintain strong bones," says Sarah Leyland, spokeswoman from the National Osteoporosis Society.

"There is currently no conclusive evidence that vitamin and mineral supplements taken, for instance, at the menopause, when bone density naturally begins to decrease, will reduce the risk of osteoporosis in later life."

There are some people with poor nutritional intakes, she says, "who might need general supplementation or specific supplements such as calcium to bring them up to recommended levels". However, for most people, a calcium-rich diet that is low in salt and with plenty of fruit and vegetables will help keep bones strong.

"Regular weight-bearing exercise such as running and walking can also play an important part. Keeping fit and active in later life will also help to prevent falls and fractures," she says.

"In addition, it may help to avoid excessive amounts of cola drinks, caffeine, alcohol and salt, as they can affect the way calcium is absorbed or excreted by the body. Try not to let your body weight get too low, as this can also have a detrimental effect on bone health; and smoking should also be avoided, to maintain healthy bones."

· For more information about osteoporosis, please contact the National Osteoporosis Society on 0845 130 3076 or email info@nos.org.uk.