New research from British and U.S. experts concluded that middle age can be very depressing to much of the world's population. 80 countries and over two million people were involved in the research, which showed that depression is very common for both women and men in their 40s.

The "U-curve" was explained by the researchers like this: we are happy when born and into our career years, are depressed and unhappy in those middle years, then return to a happy state in those golden years.

Although it's hardly possible, the ride of life can be enjoyed at every age with the right frame of mind. But, if you're in your 40s, what makes this the most unhappy time of your life? A sagging waistline and a possible career crisis? Sound off in comments below.