Canada's blood supply relies on a small number of younger donors, which might not be enough to serve the country's aging population, according to a new study.

"Like other countries, Canada's population is aging and the implications of this need to be better understood from the perspective of blood supply," said the study's lead researcher, geography Prof. Antonio Páez of McMaster University in Hamilton, Ont.

"So while younger people are more likely to donate, they are also a declining share of Canada's population," he added in a release.

Almost all Canadians will need donated blood at some point in their lifetime, but less than four per cent of eligible donors roll up their sleeves, he said.

The team analyzed records for fiscal year 2006-2007 from Canadian Blood Services, which oversees the safety of the blood supply in all provinces except Quebec.

They found those aged 15 to 24 were the most likely to donate, the team reported in Tuesday's online issue of the International Journal of Health Geographics.

The most generous age group is likely to shrink in both absolute and relative terms given long-term demographic trends at the same time that the senior population tends to increase, the study's authors said.

Canadians aged 25 to 54, who are most likely to be in the workforce, were also the least likely to give blood.

The wealthy were also less likely to donate. Immigrants were also less likely to do so, but the researchers cautioned that there could be important differences among various immigrant populations.

English-speaking Canadians and those who were highly educated or employed in health-related occupations were more likely to give blood.

People living in small cities or towns were also more likely to donate than city dwellers.

If time constraints are behind the reduced participation rates among the working age population, perhaps fine tuning the hours and location of donor clinics could help, the researchers said. But currently, donors are only asked about where they live, not where they work.

The study was funded by Canada's Social Sciences and Humanities Research Council, Canada Blood Services and Environics Analytics.