The key to a happy marriage and a happy life in retirement? According to a recent study, one answer is sex. Researchers mined a national data set called the 2004 General Social Surveys. They analyzed the responses of 238 married seniors, 65 and older, about happiness and sex. They did not examine the responses of non-married seniors, a growing sexually active group. For those, only 40 percent were very happy with life in general. Almost 60 percent were very happy in their marriage. Sixty percent were very happy with life, and 80 percent were very happy in their marriage. The researchers say the correlation held even when accounting for other factors that might keep seniors smiling, such as good health and financial stability. The findings were presented at the Gerontological Society of America’s annual meeting in Boston. The researchers say the information could help showcase the need for sexual health interventions for older Americans. So they can stay active - and active.