Women are up to 40% more likely than men to develop mental health conditions, according to new analysis by a clinical psychologist at Oxford University.
The finding, based on analysis of epidemiological studies from the UK, US, Europe, Australia and New Zealand, has significant consequences for public health, according to Prof Daniel Freeman, who said that as millions of people in the UK alone were affected by mental illness, the consequences of gender disparities were widespread. Mental health campaigners said GPs needed to be aware of such disparities when deciding how to commission resources for treatment and support.
According to Freeman's study, women are approximately 75% more likely than men to report having recently suffered from depression, and around 60% more likely to report an anxiety disorder.
Men are more likely to report substance misuse disorders – around two and a half times more frequently than women. Conditions such as ADHD (attention deficit hyperactivity disorder) and schizophrenia did not have statistically significant differences between genders in adults.
Freeman said that because the conditions most affecting women were more common than those affecting men, overall mental health conditions were more common in women than in men, by a factor of 20% to 40%.
The result is based on analysis of 12 large-scale epidemiological studies carried out across the world since the 1990s, for Freeman's new book The Stressed Sex, published by Oxford University Press. The analysis used only large-scale studies, which looked at the general population, to control for men being less likely to seek help for psychological disorders than women.
However, while pre-set criteria were used to select which studies to include and exclude, the research is not a formal meta-analysis, regarded as the gold standard of evidence.
Freeman said the differences in the types of conditions reported by genders was interesting.
"There is a pattern within – women tend to suffer more from what we call 'internal' problems like depression or sleep problems," he said. "They take out problems on themselves, as it were, where men have externalising problems, where they take things out on their environment, such as alcohol and anger problems."
He added that there was likely a complex mixture of factors contributing to the differences between the genders – related not only to physiological or biological factors, but society, too.
"Because mental health problems are extremely prevalent, if you do see an imbalance, it's an imbalance that concerns millions of people, so it's a major public health issue. The initial things we need to do is establish this fully in the UK, but also crack the issues of why," he said.
"Mental health issues are complex, they do arise from a range of factors, but we should highlight the environment, because we know discrepancies are greatest where the environment has the greatest role," he said. "Where we think it has an effect is particularly on women's self-esteem or self-worth: women tend to view themselves more negatively than men, and that is a vulnerability factor for many mental health problems."
Other academics cast a note of scepticism on Freeman's findings. Professor Kathryn Abel, of the centre for women's mental health at Manchester University, said though she hadn't had a chance to study Freeman's work in particular, there was a risk that when looking for studies to corroborate a particular thesis there was a risk of cherrypicking ones which backed it up.
Abel said that while disparities between rates of particular conditions were well-established in research, she had not seen evidence of significant differences in the overall rates of mental health disorders across lifetimes. She added that age was also a significant factor in different ratios, particularly given physical and social changes at different stages of life. She also noted that thanks to modern healthcare and society, particularly in the developed world where much of the data on rates of mental disorder comes from, "stress" by its formal definition (survival stress) is lower for women and men than at virtually any point in history.
She also considered whether some mental health conditions, though serious, were in part an effect of a relatively low-stress environment when compared with the past.
"In terms of survival, we're not exposed to stress compared with our ancestors," she said. "It is estimated that over their lifetime nearly a quarter of women will suffer a depressive illness. As a population, we are incredibly healthy, and in spite of continuing inequalities, we have never had it so good: women are living longer and more healthily than ever before – as are men.
"Some populations show lower rates of some of these arguably 'stress-related' disorders; in those countries women and men remain under far more hardship."
Abel did also note that little good-quality evidence was available to allow us to make more sense of whether or how sex differences were related to any specific physiological factors in different mental health conditions in women, as not much specific research had yet been carried out.