The decline in hip bone density after gastric bypass surgery is associated with extent of weight loss

Bariatric surgery is common and may be associated with deleterious effects on the skeleton.

Our objective was to assess bone metabolism and bone mineral density (BMD) after Roux-en-Y gastric bypass.

We conducted a 1-yr prospective longitudinal study at a university hospital bariatric surgery practice and metabolic bone disease unit.

Participants included 23 obese (mean body mass index 47 kg/m(2)) men and women, aged 20-64 yr.

Serum PTH, 25-hydroxyvitamin D, osteocalcin, and urinary N-telopeptide, and BMD were assessed.

Patients lost 45 +/- 2 kg 1 yr postoperatively (P < 0.01). PTH increased early (3 months, 43-50 pg/ml; P < 0.001) and urinary calcium dropped (161-92 mg/24 h; P < 0.01), despite doubling of calcium intake (1318-2488 mg/d; P < 0.001). Serum 25-hydroxyvitamin D concentrations were unchanged (23-26 ng/ml), although vitamin D intake increased by 260% (658 IU/d at baseline to 1698 IU/d at 12 months; P < 0.05). Markers of bone remodeling rose (P < 0.01 for both urinary N-telopeptide and osteocalcin), whereas BMD decreased at the femoral neck (9.2%, P < 0.005) and at the total hip (8.0%, P < 0.005). These declines were strongly associated with the extent of weight loss (femoral neck: r = 0.90, P < 0.0001; and total hip: r = 0.65, P = 0.02). Lumbar spine and distal radius sites did not change.

After Roux-en-Y gastric bypass, there was evidence of calcium and vitamin D malabsorption. Bone turnover increased, and hip bone density rapidly declined. The decline in hip BMD was strongly associated with weight loss itself. Vigilance for nutritional deficiencies and bone loss in patients both before and after bariatric surgery is crucial.