Impairment of Vitamin D Metabolism and Bone Mineral Content after Intestinal Bypass for Obesity

Abstract

Ten obese subjects who had undergone intestinal bypass operation (end-to-side jejunoileostomy) were studied longitudinally with respect to vitamin D and other indices of calcium metabolism. Investigations were carried out before operation (t₀) and after 6 months (t₁), 12 months (t₂), and a mean of 54 months (range. 49–58 months) (t₃) postoperatively. Serum 25-hydroxyvitamin D (25OHD) was subnormal at t₀ but after operation values declined gradually to an extremely low level at t₃, possibly because of a loss through malabsorption. Serum 24,25-dihydroxyvitamin D remained normal at t₁ and t₂ but fell to about half the normal level at t₃, probably owing to lack of its precursor, 25OHD. In contrast, serum 1,25-dihydroxyvitamin D (1,25(OH)₂D) remained normal throughout the study, indicating a marked stimulation of kidney 1α-hydroxylase activity. Serum calcium fell rapidly to a constant subnormal level, and it is concluded that the serum calcium malabsorption is due to factors other than impaired 1,25 (OH)₂D activity. Bone mineral content (BMC) was unchanged between t₀ and t₂, but thereafter (between t₂ and t₃) the mean BMC fell rapidly to about 90% of preoperative value, possibly due to a defective bone mineralization in the late postoperative period. The findings indicate a high risk of bone disease developing after intestinal bypass operation. Substitution with calcium and vitamin D should be given to these patients, but the optimal vitamin D metabolite (or combination of metabolites) for such treatment is still unknown.

Key words:

• Bone mineral content
• calcium
• intestinal bypass
• obesity
• vitamin D