Babies in Canada's North face a greater risk of developing bone-softening rickets than anywhere else in the country because of a lack of vitamin D, according to a new study.

Pregnant women in the North should take vitamin D supplements throughout the year, since the nutrient is transferred to the unborn child during the third trimester, said study author Leanne Ward, a researcher with the Children's Hospital of Eastern Ontario in Ottawa.

Following birth, however, the infants should start receiving supplements because breast milk, while it is healthy for babies, is not a good source of vitamin D, Ward said.

"Breast-fed babies, particularly those living in the North, need supplementation with vitamin D starting soon after birth," she said. "Quite frankly, the highest risk factor was in the breast-fed babies."

Rickets, which soften children's bones and can lead to bow-leggedness or fractures, are most commonly caused by a lack of vitamin D, which the body produces during exposure to sun — something many northern communities lack during the winter.

The disease is a major issue in Nunavut, where at least 31 cases have been diagnosed since the territory was established in 1999, chief medical officer of health Dr. Isaac Sobol told CBC News on Tuesday. Last year alone, health officials identified around 20 cases in children, up from only two cases in 1999-2000.

As a result, the Nunavut health department has set up a vitamin D supplementation program for mothers and infants, Sobol said.

Ward's study, conducted in 2004 and published June 28 on the Canadian Medical Association Journal's website, found the territories had the highest annual rate of rickets in the country:

• Nunavut had 155 cases per 100,000.
• The Yukon had 150 cases per 100,000.
• The Northwest Territories had 94 cases per 100,000.

By comparison, Ontario had a rate of 12 cases per 100,000, although it also had 55 per cent of all identified cases.

Ward's study surveyed 2,325 pediatricians and pediatric specialists between 2002 and 2004, asking them if they had identified any new cases of vitamin D-deficiency rickets. The study pegged the mean age for diagnosis at 1.4 years of age.