What your weight tells you about your bones

BMIIs being overweight protective for bone health? Does being underweight jeopardize bone? What happens to bone when you lose weight?

While these might seem like simple questions, the weight-bone link is far from straight-forward.  Hundreds of papers have been written on the topic, with contradictory findings.  Nonetheless I did promise to address this weighty issue, so here’s my synthesis of what we know.

  • Being significantly underweight increases the risk for fracture. Numerous studies suggest that being thin is associated with an increased risk of hip fracture compared to people of normal weight. Thin women with low bone density and little muscle mass are especially at risk.
  • Being slightly overweight may have a small protective effect on hip fractures. Weight-bearing hip fractures may be a bit less in slightly overweight women as compared to women of normal weight However, being even slightly overweight seems to be associated with a somewhat greater risk for fractures of the upper arm.
  • Being significantly overweight doesn’t protect against fractures. Even though weight-bearing bones may become stronger to carry extra weight, this doesn’t appear to ward off fractures.  Abdominal fat likely produces inflammatory compounds detrimental to bone. Being overweight is often associated with metabolic diseases like diabetes which increase fracture risk.
  • Lean body mass is important. Whatever your weight, the amount of muscle mass or lean body mass is very important. Lean body mass protects against fracture— which is why a thin person with good muscle mass will be at a lower risk than a heavy person with a lower percentage of muscle mass. Muscle mass is associated with bone mineral density, and a higher bone density associated with lower fracture risk.
  • Weight loss is associated with bone loss. Simply said, when you lose weight you lose bone.  This is especially true as we grow older, as bone loss from weight loss in post menopause isn’t regained easily.  In fact, losing weight as we age after menopause is considered a risk factor for fracture.
  • Weight cycling increases fracture risk. Weight cycling — or the losing and then gaining back of weight— is associated with increased rates of both spinal and hip fractures fracture. A stable weight, if bit above normal, is more favorable to bone.

If you’d like, in a subsequent blog I can discuss what this all might mean for you.  For now let me suggest that for women of normal or low weight, gaining a few pounds as we age is not a bad thing at all.  Read more about your possible bone health risk factors here.


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