Why does women's bone density drop after gastric bypass?

Last Updated: 2017-08-16

By Anne Harding

NEW YORK (Reuters Health) - Increases in bone-marrow fat in diabetics after gastric bypass surgery are associated with lower bone mineral density (BMD), new research shows.

Women whose marrow fat increased after the surgery had the greatest loss of BMD at both the spine and femoral neck, Dr. Tiffany Y. Kim of the University of California, San Francisco, and her colleagues found, whereas patients with the greatest improvement in hemoglobin A1c with surgery showed decreases in marrow fat.

The findings suggest that marrow fat may regulate bone formation and, in turn, that diabetes may regulate marrow fat, Dr. Kim told Reuters Health by telephone. "We're still in general learning a lot about marrow fat, so we're still just at the beginning," she said.

Evidence is growing that marrow fat is involved in bone and fat metabolism, Dr. Kim and her team note in their report, online August 9 in the Journal of Bone and Mineral Research. Larger amounts of bone-marrow fat have been linked to lower BMD and fracture risk, they add, but bone-marrow fat also increases during peak bone formation.

To better understand the role of marrow fat in bone metabolism, the researchers studied 30 obese women who underwent Roux-en-Y gastric bypass (RYGB), measuring their bone density and marrow fat levels before and six months after the surgery.

Marrow fat was unchanged in the non-diabetic participants. However, marrow fat declined by a statistically significant 6.5 percentage points, on average, in the women who had diabetes at baseline. Overall, spinal volumetric BMD fell by 6.4%, and femoral neck areal BMD decreased by 4.3% - both were significant differences.

The women who had increases in marrow fat after surgery had greater BMD loss at both the spine and femur, independent of their age and menopause status.

Women who showed the greatest improvements in hemoglobin A1c - regardless of whether or not they were diabetic - had decreases in marrow fat. Levels of insulin-like growth factor 1 were also negatively associated with marrow-fat changes.

Past research on marrow fat and bone metabolism has been cross-sectional, and the current study is the first to find a relationship between changes over time, Dr. Kim noted. The findings raise the possibility that marrow fat could someday be manipulated to prevent BMD loss after gastric bypass surgery, she added.

"Hopefully, down the road we can figure out strategies and learn more about marrow fat and diabetes to avoid these skeletal complications," she said.

SOURCE: http://bit.ly/2wenxVx

J Bone Miner Res 2017.