For a while now, I've been thinking about some of the psychological differences between men and women. In studies conducted around the world, one of the differences that turns up most reliably is the preponderance of females among those with depression.
Until puberty, males and females develop depression with about the same frequency. If anything, boys are a bit more likely to be depressed. Once puberty hits, everyone becomes more susceptible to depression—but females are twice as susceptible as males.
What is interesting is that the gender difference in rates of depression begins to wind down among those in their 50s. Another way of looking at is that depression seems to be especially, but by no means exclusively, a disorder of women in their childbearing years.
It's not clear what purpose this might serve. But there are some interesting clues about what is going on. Kenneth S. Kendler, M.D., is director of the Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University. There he presides over "the best natural experiment that God has given us to study gender differences"—thousands of pairs of opposite-sex twins. Kendler reports that efforts he has made to explain the gender difference have been "pretty stunningly unsuccessful." No major differences have panned out so far. Except one.
His studies pinpoint a significant difference between men and women in their response to adversity. "Women seem to have the capacity to be precipitated into depressive episodes at lower levels of stress."
Low levels of stress are ubiquitous for both men and women, although each of the genders reacts to a somewhat different array of difficulties. Men seem to experience more stress from job loss than women do, for example, while women are more reactive to crises in their social network.
But there are some stresses women experience that men don't. Exhibit A is role strain, carrying the load of housework and childcare while holding down a paying job. Kendler says his own wife, also a physician, once inadvertently supplied the most succinct definition of role strain when she declared, "I spend four hours a day with my kids and I feel guilty as hell, you spend two hours a day and feel like you're a great father. It's not fair."
Adding injury to insult, evidence from the physiology lab shows that women's bodies respond to stress differently than men's. They pour out higher levels of stress hormones, and they fail to shut off production of the stress hormones readily. The female sex hormone progesterone blocks the normal ability of the stress hormone system to turn itself off. Sustained exposure to glucocorticoids kills brain cells, especially the hippocampus, crucial to memory.
It's bad enough that, through the stress system, females are set up biologically to amplify internally their negative life experiences. They are prone to it psychologically too. Women ruminate more over upsetting situations, going over and over negative thoughts and feelings, especially if they have to do with relationships. Too often they get caught in a downward spiral of hopelessness and despair.
It's entirely possible that women are primed by biology to be highly sensitive to relationships. Eons ago it might have helped alert them to the possibility of abandonment while they were busy raising the children. Today, however, there's a clear downside. Ruminators are unpleasant to be around. With their oversize need for reassurance they wind up torturing those closest to them.
Of course, women have no monopoly on unpleasantness. Men fend people off, too. At least as pronounced as the female tilt to depression is the male excess of alcoholism, drug abuse and antisocial behaviors.