Serum Parathyroid Hormone Responses to Vitamin D Supplementation in Overweight/Obese Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

Abstract

Obesity is often associated with vitamin D deficiency and secondary hyperparathyroidism. Vitamin D supplementation typically leads to the reductions in serum parathyroid hormone (PTH) levels, as shown in normal weight individuals. Meanwhile, the dose of vitamin D supplementation for the suppression of PTH may differ in overweight and obese adults. We conducted a systematic review and meta-analysis of randomized controlled trials to determine the dose of vitamin D supplementation required to suppress PTH levels in overweight/obese individuals. We identified 18 studies that examined overweight or obese healthy adults who were supplemented with varying doses of vitamin D3. The primary outcomes examined were changes in PTH and serum 25-hydroxyvitamin D (25OHD) levels from baseline to post-treatment. The results of the meta-analysis showed that there was a significant treatment effect of vitamin D supplementation on PTH, total standardized mean difference (SMD) (random effects) = -0.38 (95% CI = -0.56 to -0.20), t = -4.08, p < 0.001. A significant treatment effect of vitamin D supplementation was also found on 25OHD, total SMD (random effects) = 2.27 (95% CI = 1.48 to 3.06) t = 5.62, p < 0.001. Data from available clinical trials that supplemented adults with D3 ranging from 400 IU to 5714 IU, showed that 1000 IU of vitamin D supplementation best suppressed serum PTH levels, total SMD = -0.58, while vitamin D supplementation with 4000 IU showed the greatest increase in serum 25OH levels. Vitamin D and calcium supplementation of 700 IU and 500 mg, respectively, also showed a significant treatment effect on the suppression of PTH with a total SMD = -5.30 (95% CI = -9.72 to -0.88). In conclusion, the meta analysis of available clinical trials indicates that 1000 IU vitamin D supplementation can suppress serum PTH levels, while 4000 IU of vitamin D was associated with the largest increase in serum 25OHD levels in the overweight and obese population.

Keywords: 25 hydroxy vitamin D; obesity; overweight; parathyroid hormone; vitamin D supplementation.

Figure 1

Flowchart for the process of identification of trials.

Figure 2

Forest plot of Standardized Mean Difference of PTH with vitamin D supplementation. Note: Study by Wood et al., 2014 examined overweight and obese populations separately and is listed as two separate analysis in this Forest plot.

Figure 3

Funnel Plot examining trials of PTH responses with vitamin D supplementation.

Figure 4

Forest Plot showing Standardized Mean Difference of 25OHD with vitamin D supplementation. Note: Study by Wood et al., 2014 examined overweight and obese populations separately and is listed as two separate analysis in this Forest plot.

Figure 5

Funnel Plot examining trials of 25OHD responses with vitamin D supplementation.

Figure 6

Forest plot showing Standardized Mean Difference of PTH with vitamin D and calcium supplementation. Note: Pittas et al., 2007 study included two separate study groups, once with impaired fasting glucose and another with normal fasting glucose [27].

Figure 7

Forest Plot of Standardized Mean Difference of 25OHD with vitamin D and calcium supplementation. Note: Pittas et al., 2007 study included two separate study groups, once with impaired fasting glucose and another with normal fasting glucose [27].

Figure 8

Correlation analysis of changes in 25OHD concentrations vs. changes in PTH concentrations. Pearson’s correlation coefficient is reported as r value.