Comedian Joan Rivers was known for her incisive wit and merciless self-put-downs, like this one: “I blame my mother for my poor sex life. All she told me was, ‘The man goes on top and the woman underneath.’ For three years my husband and I slept in bunk beds.” But lack of intimacy in a relationship isn’t really a laughing matter.

Sexual intimacy is (or should be) an expression of affection; affection promotes well-being; and well-being reduces stress-related health problems, including high blood pressure, sleep disorders, obesity, anxiety and depression, immune system weakness and digestive woes. But according to research published in the Archives of Sexual Behavior, Americans are having sex less frequently — overall, nine times less a year compared with 1989. Folks in their 50s, those with school-age children and those born in the 1990s are most affected.

The most common causes, according to Harvard researchers, may be from “conflicts having nothing to do with sex, like finances or child- raising issues.” Body image and self-esteem (weight gain, medical issues) and lifestyle changes or upheavals (job loss, moving, a death in the family) also have an impact.

If you and your partner are becoming less affectionate and intimate, you can turn that around. Consider family or individual therapy. Adopt a you-friendly lifestyle with physical activity and a healthy diet to change your self-image. Talk to your doctors about any concerns you have that your health or the meds you take may be negatively affecting your libido or sexual functioning.

Mehmet Oz, M.D., is host of “The Dr. Oz Show,” and Mike Roizen, M.D., is chief wellness officer and chairman of the Wellness Institute at Cleveland Clinic. Email questions to youdocsdaily@sharecare.com.