http://news.yahoo.com/s/nm/20080129/...ression_age_dc

British and U.S. researchers found that happiness for people ranging from Albania to Zimbabwe follows a U-shaped curve where life begins cheerful before turning tough during middle age and then returning to the joys of youth in the golden years.

"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."

One possibility may be that people realize they won't achieve many of their aspirations at middle age, the researchers said.

Another reason could be that after seeing their fellow middle-aged peers begin to die, people begin to value their own remaining years and embrace life once more.

But the good news is that if people make it to aged 70 and are still physically fit, they are on average as happy and mentally healthy as a 20-year old.

"For the average persons in the modern world, the dip in mental health and happiness comes on slowly, not suddenly in a single year," Oswald said. "Only in their fifties do people emerge from this low period."