They believe eating too much salt can raise the blood pressure and that this, in turn, speeds up the body's loss of calcium which could lead to osteoporosis.

High blood pressure is a major risk factor for stroke, kidney disorder and heart disease.

Osteoporosis is estimated to cost the NHS £600m a year and is an important cause of disability, particularly in elderly women.

The researchers say that their findings - the first proof of the link between hypertension and osteoporosis in humans - offer a positive health prevention message.

They suggest that changes to the diet at any age, such as cutting salt and increasing consumption of potassium-rich fruit and vegetables, could both reduce blood pressure and delay the onset of osteoporosis.

Potassium helps reduce calcium loss and lowers blood pressure.

Dr Francesco Cappuccio, the lead researcher from St George's Hospital in London, said: "People think that osteoporosis is a fact of life that they have to accept, but they should review this in light of the research. There is lots they can do."

The government recently set out guidelines encouraging salt restriction.

Health experts are working with food manufacturers to get them to reduce salt.

Bone density

The researchers measured bone density, rate of hip bone loss and blood pressure in 3,676 post-menopausal white women.

The measurements were repeated three and a half years later.

The researchers found that women with higher blood pressure had greater and faster loss of bone minerals than those with lower blood pressure.

High blood pressure is linked to strokes and heart disease

Even when adjusted for factors which affect either osteoporosis or high blood pressure, such as smoking, they found there was still a significantly greater bone loss among hypertensive women.

Bone loss was 2.26 milligrammes/square centimetres in women with the lowest blood pressure compared with 3.79 milligrammes/square centimetres for those with the highest blood pressure.

The researchers say that a cumulative loss of bone mass over many years could eventually result in osteoporosis.

In the UK, there are estimated to be just under 100,000 bone factures a year.

Doctors say the increasing number of elderly people is likely to place significant strain on health budgets so much work has gone into prevention campaigns.

The greatest risk factors for osteoporosis are poor diet in childhood and adolescence when the bones are being formed and rate of bone loss in later life.

Hormonal changes following the menopause cause a speeding up of the loss of calcium, making changes easier to measure in this age group.

Salt

Previous research shows hypertensive people excrete higher amounts of calcium in their urine than those with low blood pressure.

Writing in The Lancet, the St George's researchers believe calcium lost in the urine is replaced through calcium stripped from the bone, causing bone weakening.

They say salt plays an important role in speeding calcium loss.

However, they do not know what causes the kidneys to excrete the calcium in the first place.

"We think salt may play as big a role in osteoporosis as smoking and hormone replacement treatment," said Dr Cappuccio.