The effect of starting metformin on bone mineral density among women with type 2 diabetes in the Study of Women's Health Across the Nation (SWAN)

We examined longitudinal changes in BMD among women in the mid- life starting metformin. Study subjects were 57 years old (mean), and 36% were White. Women initiating metformin were similar to noninitiators. During the 3-year follow-up, BMD loss at all anatomic areas was similar between groups and in subgroups including baseline fasting blood glucose. Purpose/introduction Women with type 2 diabetes have higher bone mineral density (BMD), experience slower BMD loss, but have increased fracture risk. Data regarding the effect of metformin on BMD remain discordant. We examined longitudinal changes in BMD among women in the mid-life starting metformin. Methods Participants in the Study of Women's Health Across the Nation (SWAN), a diverse community-based US cohort, with BMD measurements were evaluated. Propensity score matching helped balance baseline characteristics of metformin initiators versus noninitiators. Mixed model regression tested the change in BMD between groups. Results Subjects (n = 248) were 57.4 years old (mean), and 35.9% were White. Women initiating metformin (n = 124) were similar to noninitiators ( n = 124) in age and race/ethnicity. During the median 3-year follow-up, BMD loss at all anatomic areas was similar between the metformin initiators and nonusers (all p > 0.3). Subgroup analyses including baseline fasting blood glucose showed no between-group differences. Initiation of metformin (vs. not) in peri-menopausal women was not associated with BMD changes. Conclusions Women in the mid-life starting metformin had longitudinal changes in BMD very similar to other women not starting metformin.