When it comes to health issues, diagnosis and treatment, the 1980s catch phrase does indeed ring true: Women are from Venus and men are from Mars.

It is a matter of both nature and nurture, of biology and environment, says Professor Gillian Einstein, a neurobiologist and senior scientist at the Women's College Hospital's Research Institute in Toronto.

And it is only recently that medicine has come to recognize those fundamental differences, she says. In the past, most research on how to prevent, diagnose and treat disease was done on men and the findings extrapolated to treat women.

And yet there has been clear evidence that women not only suffer diseases that men do not but they also react differently as well.

"For many years, the focus in women's health issues was almost exclusively on our reproductive systems," she says. "Now, our research and our understanding of those differences have expanded into every body system. We have come to understand that different diseases affect women differently from men and must be treated differently."

Expanding knowledge of those biological as well as social differences is an intrinsic part of the role Toronto's Women's College Hospital plays not just in Toronto but nationally and globally, Professor Einstein says. She is one of 40 researchers at the hospital, all hoping to reveal the secrets of why women are very different indeed from men when it comes to health issues.

"We are really just in early stages of understanding the complexities and repercussions of these differences but already there have been very interesting and important results," she says.

For example, Gillian Hawker and colleagues at Women's College Hospital have shown that women who have the same type and severity of knee problems as men are far less likely than men to be recommended for total knee arthroplasty by Ontario doctors; the odds of recommending total knee arthroplasty for a male patient was 22 times greater than that for a female.

Heart disease is a prime example of both the biological and social differences that affects women's care. Research shows women typically show symptoms up to 10 years later in life than men. Yet those symptoms often go unrecognized and, even when they are, men receive medical attention more quickly and more frequently. Women's Hospital researchers have shown that men are also referred to cardiac rehabilitation programs more often than women. Both gender and sex affect the etiology and course of the differences in these conditions between women and men.

One of Professor Einstein's current research projects is both ambitious and vital to understanding sex-based differences in response to our environment. She is using modern diagnostic equipment to map women's brains to understand how various parts of the body and its internal systems are represented in the female brain and how that representation might change depending on estrogens.

"Dr. Wilder Penfield did the ground-breaking work of map-ping the human brain years ago at the Montreal Neurological Institute but almost all his subjects were men," she says. "We believe that there may be significant differences between women and men."

If Professor Einstein is able to connect how the female brain reacts to and processes stimuli from the body, other researchers can build on that fundamental knowledge to address a host of other issues.

For example, why are women twice as likely to be diagnosed with depression than men? Is it brain or environment? Or, as is most likely, both?

"Obviously, the differences go beyond having two X chromosomes or an X and a Y chromosome," she says. "In women and men, it is a combination of nature and nurture -- of biological systems and the ways in which the environment nteracts with them.

"Women's College Hospital is addressing both."