Abnormalities of vitamin D and calcium metabolism after surgical treatment of morbid obesity: a study of 136 patients.

OBJECTIVE

To assess the effect of bariatric surgical treatment of morbid obesity on bone mineral metabolism.

METHODS

We analyzed pertinent vitamin D and calcium metabolic variables in 136 patients who had undergone a malabsorptive bariatric operation. Measurements of bone mineral density (BMD), serum 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D [1,25-(OH)2D], parathyroid hormone (PTH), calcium, phosphorus, and alkaline phosphatase were performed. Statistical analyses assessed correlations among various factors.

RESULTS

The mean age (+/-SD) of the study group was 48.34 +/- 10.28 years. Their mean weight loss was 114.55 +/- 45.66 lb, and the mean duration since the bariatric surgical procedure was 54.02 +/- 51.88 months. Seventeen patients (12.5%) had a T-score of -2.5 or less, and 54 patients (39.7%) had a T-score between -1.0 and -2.5. Of 119 patients in whom serum 25-OHD was measured, 40 (34%) had severe hypovitaminosis D (25-OHD <8ng/mL), and 50 patients (42%) had low hypovitaminosis D (serum 25-OHD 8 to 20 ng/mL). The magnitude of weight loss correlated negatively with serum 25-OHD, calcium, phosphorus, and calcium x phosphorus product values and positively with serum alkaline phosphatase level. Serum 25-OHD and calcium concentrations correlated positively with the BMD. PTH, serum 1,25-(OH)2D, and alkaline phosphatase concentrations correlated negatively with the BMD, a reflection of the presence of secondary hyperparathyroidism, an accelerated conversion of 25-OHD to 1,25-(OH)2D by the elevated PTH levels, and increased osteoblastic activity. The mean daily vitamin D supplementation was 6,472 +/- 9,736 IU.

CONCLUSION

Hypovitaminosis D and subsequent bone loss are common in patients who have undergone a bariatric surgical procedure for morbid obesity. These patients require rigorous vitamin D supplementation.