Patients with low vitamin D levels who take vitamin D supplements might experience suppressed bone turnover, potentially from parathyroid hormone (PTH) reduction, according to study results published in Bone.

To investigate the effects of vitamin D supplementation on bone turnover markers, including procollagen of type 1 amino-terminal propeptide (PINP) and carboxyl-terminal telopeptide of type 1 collagen (CTX-1) and other bone-related substances in patients with vitamin D deficiency, researchers randomly assigned 399 individuals with a baseline serum 25-hydroxyvitamin D (25(OH)D) level <42 nmol/L to receive vitamin D3 20,000 IU/week or placebo for 4 months. Levels of 25(OH)D were similar between groups at baseline.

Compared with the placebo group (n = 197), which experienced an average 25(OH)D decrease of 4.5 nmol/L by study end, the treatment group (n = 202) had an average increase of 56.1 nmol/L. Furthermore, patients who received vitamin D supplementation had a significant decrease in serum PTH, an increase in calcium, and a slight but significant decrease in PINP (P <.01).

There were no significant effects in levels of CTX-1, Dickkopf-1, sclerostin, tumor necrosis factor-alpha, osteoprotegerin, receptor activator of nuclear factor kB ligand, or leptin. In addition, subgroup analyses of subjects with lower baseline 25(OH)D levels (<25 nmol/L) yielded no additional effects.

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Reduction of PINP was more significant in treated individuals who had baseline PTH levels >6.5 pmol/L and showed a posttreatment decrease. These individuals also experienced significantly reduced levels of CTX-1 and increased sclerostin.

Several limitations were noted for this study, including an absence of data on participants’ calcium intake.

“[V]itamin D supplementation has minor effects on [bone turnover markers] in subjects without extreme vitamin D deficiency,” the researchers said. “Thus, bone turnover markers are probably not useful in monitoring skeletal response to vitamin D supplements. Intervention studies including subjects with higher baseline serum 25(OH)D than in our study, should be discouraged.”

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Reference

Jorde R, Stunes AK, Kubiak J, et al. Effects of vitamin D supplementation on bone turnover markers and other bone-related substances in subjects with vitamin D deficiency. Bone. 2019;124:7-13.