For years, scientists studying the brain used only male rodents as their subjects, not wanting the females' ovarian cycles - and inconveniently changing hormone levels - to muddy their research.
With women now accounting for 70% of new dementia cases and succumbing to depression twice as often as men, that research bias is starting to crumble, with a growing realization that hormone variations are actually a key factor in why some brain disorders affect women and men so differently.
A conference Tuesday in Toronto is being touted as the first of its kind in Canada, a chance to underscore the neurological divide between the sexes, as the aging population creates an expected tidal wave of Alzheimer's disease.
Understanding those differences and figuring out ways to lessen the number of women who get Alzheimer's and depression is crucial, given the key role they play in caring for dementia patients, says one scientist speaking at the event.
"We need to shine a special light on it, absolutely," said Nasreen Khatri, a clinical psychologist at Baycrest, the brain and aging centre whose charitable foundation is spearheading the conference. (The National Post is a media sponsor of the symposium.)
"As these women get older we don't want them to develop dementia, because who will care for them? We need them to be intact, for their own sake and for the sake of society."
In basic science involving animals and in testing of drugs and other research on humans, subjects have predominately been male for a variety of reasons, said Dr. Gillian Einstein, a University of Toronto psychology professor.
That includes, for humans, a desire to protect women from experimental medicines that might harm pregnancies, and, for animals, the fact that it is cheaper to use lab rats or mice that are male, rather than sacrifice females that breed and produce more subjects, she said.
It was also felt that the menstrual cycle - just four days in a rodent - and its varying levels of hormone could complicate results, said Dr. Einstein.
She argues there are many reasons for scientists to now focus more on the brain's sex distinctions, noting that males are more prone to some neurological problems, such as autism, than women.
The Baycrest conference is focused on Alzheimer's, which already affects 500,000 Canadians and is expected to hit about 1.1 million patients within 25 years, imposing hardship on family caregivers as well as patients and a burden on the health-care system.
What may not be well known is that seven out of 10 new cases are women, ironically the people who more often than not take on the major responsibility for caring for dementia sufferers.
One key factor is likely reduced estrogen levels, one of the effects of menopause, said Dr. Einstein.
Research shows that women who have hysterectomies or ovaries removed before menopause - both operations that would cut estrogen production - are far more prone to dementia.
Though there is no proof yet of a cause-and-effect relationship, it is known that estrogen helps in the connections between neurons and the firing of neurons, she said.
"If you have a vulnerability that predisposes you to Alzheimer's disease, and if you aren't making estrogens, it can kick you over that cognitive cliff," said the researcher. "For lateonset Alzheimer's disease, actually being estrogen-deprived ... is a kind of a risk factor."
Complicating the issue is that estrogen, though good for the brain, is actually considered a risk factor for some forms of breast cancer. A possible answer are drugs that could boost the estrogen level only in the brain, said Dr.
Einstein. But research on hormone-replacement treatments has all but ground to a halt since findings in 2002 that suggested such HRTs increase the risk of breast cancer, stroke and heart attacks.
Almost as striking as the sex differences involving Alzheimer's is that women are twice as likely to develop depression. The higher risk is likely due to a combination of factors, including such biological ones as the effects on the brain of hormonal changes during pregnancy, social factors like the multiple roles women tend to play in modern society and psychological ones like different coping styles, said Dr. Khatri.
Many middle-aged women today are also caring for both their own children and elderly parents, increasing stress levels, which in turn can lead to depression, she said. And depression itself appears to make women two times as susceptible to Alzheimer's, for reasons that are not entirely clear, said Dr. Khatri.
Regardless, it makes successfully treating depression all the more important.
"We don't want them to get depressed again and again in case it makes them more likely to get dementia later on."
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