As warnings about the growing levels of average Canadian household debt relative to income escalate, a report from CIBC says those averages hide the even scarier fact of just who is racking up the most debt.

“A rising share of the highly indebted are over 45 years old, an age when accumulating net assets ahead of retirement should be paramount,” Avery Shenfeld, the bank’s chief economist, said in the report published Thursday.

Canada’s debt-to-disposable income ratio has been marching ever higher, rising to 153% in the third quarter of 2011, up from 148% a year earlier, according to Statistics Canada.

But the share of those over 45 among the high-debt burden portion of the population has been “rising much faster than their share of the overall population,” Mr. Shenfeld said. In 2007, the share was slightly more than 36% and by 2011, it was more than 43%, according to the report.

“Canadians nearing retirement who should be in their prime savings years are, instead, getting themselves deeper into debt,” he said.

It’s not just those heading into their golden years who are accumulating more debt, but also those who have already dug themselves into a hole.

In general, the growth in debt-to-income ratios is coming from those already highly indebted households, “rather than from less indebted households getting drawn to the punchbowl by the promise of low rates,” Mr. Shenfeld said.

All of the rise in debt since 2007 has come from high-debt-burden households, defined as a ratio of 1.6 or higher for debt-to-gross income, the report said. Meanwhile, medium and light-debt households have reduced their share of total household debt.

High-debt-burden households, which now make up 34% of households with debt, are also struggling to build up assets.

These households have accumulated less than 4% in assets since 2007, compared with about a 10% increase for those with more moderate debt-to-income burdens, the report said.

The report paints a bleak picture about Canadians’ room to take on additional debt if necessary and spend economy-boosting money.

But all is not lost.

Canada is not yet on the “precipice of a wave of defaults,” Mr. Shenfeld said, noting that an unlikely combination of sharply rising interest rates along with a steep jump in unemployment would be necessary to trigger a spike in bankruptcies.