New Delhi, Aug. 1 -- NEW YORK - She had been in and out of therapy for three years when her psychiatrist finally asked. Not about her sleep, not about her medications. About sex. How often. When it had last felt wanted rather than obligatory. The question was uncomfortable, and then, she would later say, it was the most useful one she had been asked.

A cross-sectional study published in the Journal of Affective Disorders found that adults who had sex once or twice a week were 24 percent less likely to screen positive for depression than those who reported being sexually inactive. The research, conducted on a nationally representative sample of young and middle-aged adults in the United States, adds statistical weight to a question many m...