The healthy immigrant effect persists, according to a Statistics Canada study released Wednesday that found immigrants are generally healthier than Canadian-born citizens.

Some healthy people who immigrate to Canada find their health deteriorating after their arrival, but little is known about why the edge in health declines for immigrants the longer they live in Canada.

The mortality rate for newcomers continued to be lower than for Canadian-born residents, even after immigrants have lived here more than 20 years, the new study suggested.

The study does not examine the reasons immigrants tend to have better health, but those are likely to include the screening that selects an inherently healthier group of people who arrive in Canada, and also those who have a healthier diet and are more physically active in their native countries.

The longer the immigrants live in Canada, the more closely they adopt the patterns and behaviours common here.

The relationship between immigration and health has become more difficult to determine, however, as the origins and demographics of immigrants to Canada have changed.

Statistics Canada's current analysis relies on the 1991-2001 Canadian mortality followup study, which examined 2.7 million people, of which 552,300, or 20 per cent, were immigrants.

Immigrants had significantly lower mortality rates than Canadian-born people: 1,006 versus 1,305 for men, and 610 versus 731 for women.

In 2006, immigrants made up 19.8 per cent of Canada’s population, a proportion that is expected to increase to at least 25 per cent by 2031, Statistics Canada says.

Mortality rates differ according to the origins of immigrants, and the study suggests there is a need for more in-depth analysis of health by country of origin.