Closing in on 40? 50? Feel like life is passing, er, has passed you by? Maybe even left you in the dust? You're not alone. In fact, new research shows that fellow midlifers throughout the world--or at least a significant chunk of it--share your pain. But fear not: if you endure, the study shows, things will begin looking up again, once you get over that speed bump in the road of life called (gasp!) middle age.

Researchers from Dartmouth College in Hanover, N.H., and the University of Warwick in Coventry, England, after scouring 35 years worth of data on two million people from 80 nations, have concluded that there is, indeed, a consistent pattern in depression and happiness levels that is age-related and leaves us most blue during midlife.

According to the study, set to be published in the journal Social Science & Medicine, happiness follows a U-shaped curve: It is highest at the beginning and end of our lives and lowest in-between.

The researchers found that the peak of depression for both men and women in the U.K. is around 44 years of age; in the U.S., women on average are most miserable at age 40 whereas men are when they hit 50. They found a similar pattern in 70 other countries.

So what's at the root of this depressing dip? Not sure, say authors Andrew Oswald of Warwick University and Dartmouth's David Blanchflower, both economists. But they speculate, as Oswald put it, that "something happens deep inside humans" to bring us down rather than shattering events (such as divorce or job loss), because it tends to creep up on us over time.

"Some people suffer more than others, but in our data the average effect is large. It happens to men and women, to single and married people, to rich and poor and to those with and without children," Oswald said. "Nobody knows why we see this consistency."

"What causes this apparently U-shaped curve, and its similar shape in different parts of the developed and even often developing world, is unknown. However, one possibility is that individuals learn to adapt to their strengths and weaknesses, and in midlife quell their infeasible aspirations," he added. "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 good news: the data show that most people emerge from this low ebb in their 50s. And, "by the time you are 70, if you are still physically fit, then on average you are as happy and mentally healthy as a 20-year old," Oswald said. "Perhaps realizing that such feelings are completely normal in midlife might even help individuals survive this phase better."

Mind you, not everyone agrees. Other studies have shown similar such curves in many countries, but there are exceptions; it has been reported that in some places middle-aged folks are quite happy. In fact, reaching middle age in some parts of the world is considered something to be proud of. (Imagine that.) But if you're not one of those perky midlifers, remember this: you may be down in the dumps now--but it won't be long before you're on the brink of bliss.