Abnormalities of circulating 25-OH vitamin D after jejunal-lleal bypass for obesity: evidence of an adaptive response.

Circulating levels of 25-OH vitamin D were measured in 44 patients who had undergone small intestinal bypass for obesity. Sixty-one percent had low circulating levels of the metabolite, which tended to normalize with time. This adaptive response also occurred for circulating total calcium, magnesium, albumin, and alkaline phosphatase. Serum concentrations of 25-OH vitamin D were directly related to total serum calcium and albumin. Impaired intestinal absorption of 25-OH vitamin D was seen in two patients. Following correction of total serum calcium for attendant hypoalbuminemia, 27% of patients remained hypocalcemic. The bone densities of two of 32 patients were low. In addition, skeletal biopsies of three of six patients were abnormal. It is concluded that small intestinal bypass results in at least transient deficits of circulating 25-OH vitamin D. As this operation may be associated with abnormal bone morphology, clinically significant skeletal disease may become apparent with long-term follow-up.