If you think turning 40 is bad, just wait until you turn 44. Researchers say that’s the age when people feel most depressed.

Using data on two million people from 80 countries, researchers found an extraordinarily consistent pattern in depression and happiness levels that leaves us most miserable in middle age.

Using a sample of one million people from the U.K., researchers discovered that for both men and women the probability of depression peaks around 44 years of age.

The only country which recorded a significant gender difference was in the U.S., where unhappiness reached a peak at around 40 for women and 50 for men.

"Some people suffer more than others but in our data the average effect is large," said Professor Andrew Oswald, a University of Warwick Economist in a news release. "It happens to men and women, to single and married people, to rich and poor, and to those with and without children."

Oswald added that while nobody quite knows why we see this consistency, he said he has some theories of his own.

"One possibility is that individuals learn to adapt to their strengths and weaknesses, and in mid-life quell their infeasible aspirations,” he said. “Another possibility is that cheerful people live systematically longer. A third possibility is that a kind of comparison process is at work in which people have seen similar-aged peers die and value more their own remaining years. Perhaps people somehow learn to count their blessings."

The study, by the University of Warwick in Britain and Dartmouth College in New Hampshire will be published in the journal, Social Science & Medicine.