For overweight and obese individuals, taking 1000 IU of vitamin D3 supplements daily can reduce serum parathyroid hormone (PTH) levels, according to a new systematic review and meta-analysis.

“Although our meta-analysis reveals a small effect size, our data do support a true effect of 1000 IU of vitamin D supplementation in the suppression of PTH,” Deeptha Sukumar, PhD, of Drexel University in Philadelphia, and colleagues wrote in Nutrients. “In all of the reviewed studies, the control groups showed no significant changes in PTH.”

Adults with low vitamin D levels tend to experience PTH increases, including those considered obese. While debatable, the Institute of Medicine defines vitamin D inadequacy as a level of 12 to 20 ng/mL and deficiency as a level below 12 ng/mL.

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Although the general recommended dietary allowance of vitamin D for adults is 600 IU, the amount required to raise serum 25-hydroxyvitamin D (25OHD) levels in overweight and obese individuals likely differs, previous research suggests. In normal weight adults, the investigators stated, every 1000 IU of vitamin D supplementation increased serum 25OHD by 4.8 to 20 ng/mL, based on prior studies.

For the current study, the team culled and analyzed 18 randomized controlled trials of overweight and obese adults (body mass index 25 kg/m2 and above) receiving 400 to 5714 IU of vitamin D3 supplements daily for 12 weeks to 3 years to identify effective doses of the vitamin. All patients were free of renal disease.

Meta-analyses demonstrated that a statistically significant suppression of PTH and increase in serum 25-hydroxyvitamin D levels occurred after vitamin D3 supplementation. The team found that 1000 IU of vitamin D3 best reduced PTH levels, while a dose of 4000 IU best increased 25OHD levels. A subset of studies also showed that a combination of 700 IU vitamin D and 500 mg calcium likewise suppressed PTH.

Inadequate sun exposure, altered vitamin D activation, and greater storage of vitamin D in fat tissue are some of the factors believed to contribute to low serum 25OHD levels in the overweight population, they explained.

The investigators were unable to conduct separate analyses by overweight and obese categories, which is a limitation. Although other research suggests that age and gender influence PTH suppression, the team did not have sufficient data on these factors. Future research is still needed to clarify these effects and the optimal formulations of vitamin D.

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1. Lotito A, Teramoto M, Cheung M, Becker K, and Sukumar D. Serum Parathyroid Hormone Responses to Vitamin D Supplementation in Overweight/Obese Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Nutrients 2017, 9, 241; doi: 10.3390/nu9030241