Montreal researchers have discovered that patients using inhaled steroids increase their chances of developing diabetes.

Patients with lung disease should ask their physicians about treatment with the synthetic hormone medication because the higher the dose, the greater the risk, said Samy Suissa, director of the Centre for Clinical Epidemiology at the Lady Davis Institute for Medical of the Jewish General Hospital.

Oral corticosteroids like prednisone have long been known to increase the risk of diabetes, but this is the first time the effect has been observed with the inhaled form, said Suissa, lead author of the study published in the American Journal of Medicine.

Inhaled steroids have become the mainstay of medical treatment of asthma and chronic obstructive pulmonary disease (COPD), the new name for emphysema and chronic bronchitis.

But they have been shown to increase the risk of cataracts and pneumonia, "and now we are finding the increase in diabetes," said Suissa, a professor of epidemiology and biostatistics at McGill University.

Dipping into Quebec's database kept by the provincial health insurance board, the Régie de l'assurance maladie du Québec, Suissa's team studied 400,000 patients over 18 years.

The study determined that inhaled steroids increased the rate of onset of diabetes by 34 per cent for every year of use, from 14 people per 1,000, to 19 per 1,000.

"That would be okay if these drugs worked in COPD, but unfortunately the data that we have suggests they don't for the majority of these patients," he said.

In asthma patients inhaled steroids are extremely effective in controlling the disease by reducing the airway inflammation that can lead to fatal asthma attacks.

It saves lives and reduce hospitalization, Suissa said.

"I would not be concerned about the risk," he added.

But the same medication does not have the same benefit for COPD whose lung decline is primarily caused by smoking. About 70 per cent of COPD patients rely on bronco-dilator, aerosol sprays and micropowders, and usually in high doses.

"It would be okay if these drugs worked ... but data says it works for a few," Suissa said, that is, in a small subset of COPD patients who also have asthma.

The question is, if it's not effective is it safe? Suissa demanded.

"Clearly the benefits outweigh by far the risk," he said.

Physicians should reserve the use of inhaled steroids for asthma patients who can really benefit from them while reassessing COPD patients for lowest effective dose. In all cases, these patients should be monitored for high blood sugar and insulin resistance, he added.