Blocking serotonin production may form the basis of a new treatment for osteoporosis, results of a US study suggest.

In addition to its role in the brain, serotonin is also produced in the gut, where it has been found to inhibit bone formation.

University of Columbia researchers studied the effect of inhibiting the enzyme tryptophan hydroxylase, which is involved in serotonin synthesis.

Treatment with a drug that blocks the enzyme's action decreased serotonin levels in rats. In addition, six weeks' treatment with the drug increased bone formation in the rats.

The drug did not appear to cross the blood/brain barrier and so had no effect on brain levels of serotonin.

In addition, the researchers found that decreasing the level of gut-derived serotonin did not lead to GI or haematological side-effects.

'Given the progressive ageing of the general population, postmenopausal osteoporosis is a growing public health concern,' the researchers said.

'There is a major need to identify safe anabolic agents that can increase bone formation on a long-term basis.'

Although parathyroid hormone is effective at treating osteoporosis, it has to be injected daily and can only be taken for two years, limiting its use as a long-term agent.

The researchers believe their findings could have major implications for the treatment of osteoporosis.

'The fact that this molecule can be administered orally, promotes only bone formation and is needed at a relatively small dose, suggests that inhibitors of gut-derived serotonin synthesis have the potential to both prevent and treat osteoporosis,' they said.

Osteoporosis affects over three million people in the UK and is a cause of significant morbidity and mortality, resulting in around 200,000 fractures a year.

• Nature Medicine Online 2010