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A new Canadian study shows that middle-aged women face far greater risks of heart disease than men as a result of depression.

“We are learning that depression knows very little about political correctness,” said Roger McIntyre, head of the Mood Disorders Psychopharmacology Unit at Toronto's University Health Network.

This study shows for the first time that depression affects women in ways that are much more significant and much more physically severe than in men, he said.

The study, published in Health Reports, a Statistics Canada publication, used data from a national sample of 4,948 men and women aged 40 or older who were followed for 12 years starting in 1994-1995. The goal was to determine whether depression was linked with a higher risk of a heart disease. It was the first time the interplay between depression and heart disease among Canadians had been studied at a national level.

“Men can still get heart disease if they suffer from depression,” said Heather Gilmour, an analyst with Statistics Canada and the lead researcher on the study. “But in this study it was far less likely to happen than in women.”

The study found that of the people surveyed, 19 per cent of men and 15 per cent of women had developed or died from heart disease by 2006-2007.

But women who experienced depression were at a 70-per-cent greater risk of developing heart disease than women without depression – a large enough percentage to show a causal connection. In contrast, depressed men showed no greater risk of developing heart disease than other men.

The correlation between heart disease and depression has been well documented in past studies. People who are depressed tend to neglect their health, sleeping and eating poorly, smoking and drinking to excess and eschewing exercise – all of which leads to greater incidences of heart disease, among other conditions.

But the relationship is more complex than that, Dr. McIntyre said. The bodies of people with depression become disrupted and experience a host of changes that may trigger heart disease, he said, and these effects are more likely to be more pronounced in women.

“Their blood gets sticky, which leads to clotting, their heart rhythm is abnormal, hormone levels are abnormal, and their metabolism slows,” he said. “Some of these changes, along with economic and lifestyle factors, are likely why we see such high rates of heart disease.”

As a result, women experience a larger physical burden from depression, Dr. McIntyre said. They also tend to experience depression earlier in life and are more likely to have recurrences, he said. They're more likely to have migraine headaches and anxiety disorders as a result of depression.

Dr. McIntyre said depression also pushes up the levels of stress hormones such as cortisol. Elevated cortisol levels can impair insulin sensitivity in the body and encourage belly fat, a risk factor for heart disease that's more likely to affect women's health, he said.

“The actual illness itself is often much more severe in women, which distinguishes them from men and puts them at higher risk of getting cardiovascular disease,” he said.

There is a caveat, however: Ms. Gilmour allowed that the study may not have had a long enough follow-up period. The onset of depression occurs earlier in women and heart disease develops over time, which may explain why depressed men in the study showed lower rates of heart disease, she said.

Ms. Gilmour said she plans to study the data over a greater length of time to see if the pattern continues. “The trend is there,” she said. “It just needs to be studied over a longer period.”

With a report from The Canadian Press