Middle age makes you miserable, so don't blame your job, your kids, your spouse, your income or lack of it, suggests an international study of 2 million people from 80 nations released today.
Researchers from Great Britain and the USA analyzed data spanning more than 35 years on measures such as depression, anxiety, mental well-being, happiness and life satisfaction.
They found that men and women in their 40s were more likely to be depressed and weren't as happy as other ages. Middle age is such a low point for well-being that it's at the bottom of a U-shaped curve that indicates greater happiness among the young and old.
"It's midlife per se," says co-author Andrew Oswald, an economist at the University of Warwick in Coventry, England. "It's something deep beyond all the controls in our equation. It's a developing midlife low. It doesn't just happen one year and go away another."
For both sexes, the probability of depression peaks around age 44.
Oswald doesn't have any concrete answers on why such a slump occurs.
"My best conjecture is that people eventually learn to quell their infeasible aspirations," he says. "They manage to get their expectations into line with what they can actually achieve."
The study by Oswald and fellow economist David Blanchflower of Dartmouth College in Hanover, N.H., being published in the journal Social Science & Medicine found the same U-shape by age for 72 of 80 countries studied.
"You can be almost certain you will follow this U-shaped curve," Oswald says. "If you are finding life tough in your 40s, maybe it's useful to know this is completely normal."
The research found a less pronounced age factor in developing countries.
Others who study happiness are less convinced this midlife slump is all about age.
"In order to prove that, you can't just prove the other things are wrong. You have to get evidence to measure that," says Ed Diener, a psychologist at the University of Illinois at Urbana-Champaign, who has studied happiness for more than 30 years.
"I'm not saying it's impossible, but I would be careful about jumping too quickly on some biological factor."
Research by Angus Deaton, a Princeton University economist, has found a similar U-shaped curve in some countries, but he says it doesn't hold true globally.
"Young people are happier in some countries, and in some countries middle-aged are happy. It depends on which country," he says. "In my data, it's true if you look some places, older people are really miserable relative to younger people. It's not U-shaped. (Happiness is) just going down."
Despite the skepticism, Oswald says the age factor appears real.
"We're correlating mental well-being with age, having factored out 100 other influences," Oswald says.
"In 2008, social science can't do better than this."