Unfortunately, your friend may be right. Estrogen replacement therapy (ERT) was linked to back problems in a group of 7,209 white women over age 65.

In this study, women on ERT were generally healthier than those who had never used estrogen. Nevertheless, 53 percent of women on ERT reported back pain in the previous year, as opposed to 43 percent of those who had never used ERT. Twelve percent of women using ERT said their back pain made daily activities difficult. This was true for only nine percent of women who had never used estrogen.

Researchers think that estrogen may have a loosening effect on joints. Estrogen may cause more movement in the spine and less elasticity (or support) in the tissues around it. Together, these things may cause back pain in women using ERT.

Is this a reason not to take estrogen? Not necessarily. But you may want to work with your doctor or physical therapist to take special care of your back while you're on ERT.