A new form of vitamin D has emerged as a promising possible treatment for the crippling disease osteoporosis, say scientists.

Thousands of people, many of them post-menopausal women, suffer from the condition, which can increase the risk of damaging fractures.

In animals with conditions similar to osteoporosis, the vitamin increased bone density.

Dr Hector DeLuca, from the University of Wisconsin-Madison, conceded a new drug could be several years off but said it could eventually be important.

Bone building drugs - that work on the cells that create new bone - are certainly an area of considerable interest

Spokesman, National Osteoporosis Society

He said: "From where I sit, this is the most promising vitamin D compound I've seen."

He suggested that the compound could one day be an alternative to hormone replacement therapy, often used by post-menopausal women to halt bone loss.

Long-term use of HRT has been linked with an increased risk of certain diseases, such as cancer or thrombosis.

The laboratory tests involved rats whose ovaries were removed to mimic the menopause.

Animals given the new vitamin D analogue managed to achieve a 9% increase in total body bone mass.

More importantly, vertebrae - which tend to be worst affected by osteoporosis - in the treated rats showed a 25% improvement.

Side-effects

The compound appears not to show any toxic side-effects, although much more safety testing will be needed.

Dr DeLuca said: "We've got a compound that is very selective for bone. It is very effective in animals."

He suggested that, even at relatively low concentrations, the compound might possess a "unique capacity" to induce genes which start the bone-building process.

A spokesman for the National Osteoporosis Society said: "It's always interesting to see new pieces of research into the treatment of osteoporosis and we will now be studying the contents of this American paper.

"Bone building drugs - that work on the cells that create new bone - are certainly an area of considerable interest in the treatment of osteoporosis.

"Most treatments currently licensed for the disease work by slowing down the breakdown of bone so to find treatments that actually work on building new bone is considered to be one of the ways forward to tackle this disease.

"It is therefore always encouraging to hear about new pieces of research in this area."

The study was published in the journal The Proceedings of the National Academy of Sciences.