Happiness is U-shaped, for we are happier at the start and end of our lives but hit a slump¹ when we are aged³" target="_blank">middle-aged², British and US researchers say.

Economists⁴ from the University of Warwick, central England, and from Dartmouth College, New Hampshire, looked at data on the mental health of two million people from 80 countries.

In Britain, the probability of depression for men and women peaks at around 44 years of age, Warwick University said in a press release.

In the United States, though, there was a big difference between men and women.

Among women, unhappiness peaked at around the age of 40, whereas among men, it was about 50.

But the U-shape of happiness is constant around the world, and mid-life depression occurs regardless of marital⁵ status, changes in job or income.

The study appears in Social Science & Medicine, published by the Dutch publishing house Elsevier.

"It happens to men and women, to single and married people, to rich and poor, and to those with and without children." said co-author Andrew Oswald.

One possibility may be that people realize they won't achieve many of their aspirations⁶ 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 physically⁷ 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."

英美两国的研究人员称，人一生的快乐呈U形走向，童年和老年时期最快乐，中年时期处于最低谷。

英格兰中部沃维克大学和美国新罕布什尔州达特茅斯学院的经济学家们对80个国家的200万人的心理健康数据进行了研究分析。

沃维克大学在新闻发布会上说，英国的男性和女性在44岁左右最郁闷。

而在美国，男性和女性则有很大差别。

女性在40岁时最不开心，而男性则在50岁左右。

但从世界范围看，人们的快乐水平普遍呈U形走向，而且人到中年出现情绪低落与婚姻状况、工作变化以及收入多少等因素都无关。

研究报告在荷兰埃尔塞韦尔出版社出版的《社会科学与医学》上发表。

研究报告撰写者之一安德鲁•奥斯瓦尔德说：“无论男性女性、是否结婚、贫穷还是富裕、有无子女，人人都会遭遇中年时期的低谷。”

研究人员称，有一种可能是，人到中年后会意识到自己的很多理想已经不可能再实现。

也可能是因为人到中年后目睹了一些同龄人的离世，所以开始珍惜余下的岁月，并再次拥抱生活。

但庆幸的是，如果你到了70岁，身体还很健康，那么你会像20岁时一样快乐。

奥斯瓦尔德说：“对于现代社会的人们来说，中年的低谷是慢慢到来的，并不是某一年突然发生的。到了50多岁时，人们就能慢慢走出这个低谷了。”