Bone mineral density (BMD)

Bone mineral density is how much mineral is packed into a given area of bone, measured by a DXA scan and reported in grams per square centimeter. It is the standard way osteoporosis is diagnosed, and NIAMS — the NIH institute for bone and joint disease — describes the DXA scan as the usual test used to make that diagnosis and to track bone health over time.

The concern in weight-loss medicine is straightforward: bone adapts to the load it carries, so losing a large amount of weight removes some of the stimulus that maintained it. That applies to dieting and to bariatric surgery as much as to medication.

The GLP-1-specific evidence is more reassuring than the worry suggests, though it is not the last word. A 2025 systematic review and meta-analysis of 25 studies in type 2 diabetes found that GLP-1 receptor agonists were not significantly associated with increased fracture risk (relative risk 0.80, confidence interval 0.47 to 1.36). It also reported small but statistically significant improvements in lumbar spine, femoral neck and total hip BMD versus control, along with changes in several bone turnover markers. The authors were explicit that limitations remain and that longer, higher-quality studies are needed.

Two caveats keep that in proportion. Those studies were in people with type 2 diabetes, not the newer high-dose weight-management populations, and the weight losses involved were generally smaller than what semaglutide 2.4 mg or tirzepatide produce today. Fracture is also a rare outcome, so a wide confidence interval means the question is open rather than closed.

Worth asking your clinician: whether your age, sex, family history or prior fractures warrant a baseline DXA scan; whether your calcium and vitamin D intake are adequate; and whether weight-bearing and resistance exercise should be part of your plan. Our bone density and fracture risk review, bone and fracture study roundup and exercise configurator go further.