Impact of body composition on vitamin D requirements in healthy adults with vitamin D deficiency.

2025-07-03
Frontiers in endocrinology 16
- Dexing Dai
- Yali Ling
- Feng Xu
- Haibo Li
- Rui Wang
- Yingying Gu
- Xuedi Xia
- An Xiong
- Ruoman Sun
- Lei Qiu
- Ya Ding
- Yixin Yu
- Xueyang Cai
- Zhongjian Xie

PubMed: 40678321
DOI: 10.3389/fendo.2025.1421663

Study Design

Type: Randomized Controlled Trial (RCT)
Sample size: n = 20
Population: 20 healthy adults with vitamin D deficiency, divided into ≤1,200,000 IU (n=10) and ≥2,400,000 IU (n=15) groups
Methods: Subjects received multiple intramuscular injections of vitamin D2 until serum 25(OH)D >30 ng/mL; all received two i.m. injections of 600,000 IU vitamin D2 with dose adjustments every 6 weeks; body composition measured by DXA and corrected using FMI; serum levels by LC-MS/MS
Duration: every 6 weeks (dose adjustments), total duration not explicitly stated
Funding: Unclear

Background

Previous studies have shown that individuals with high body mass index typically require high doses of vitamin D supplementation to correct vitamin D deficiency. However, it is unclear which specific body composition is the determining factor affecting the bioavailability of vitamin D after supplementation. The aim of this study was to determine which body components affect the bioavailability of vitamin D.

Methods

In order to ensure the compliance of the study subjects and avoid the impact of sunlight on vitamin D₃ levels, the subjects received multiple intramuscular (i.m.) injections of vitamin D₂ until their serum levels of 25-hydroxyvitamin D [25(OH)D] were above 30 ng/mL. All subjects received two i.m. injections of 600,000 IU vitamin D₂, and dose adjustments were made every 6 weeks based on whether serum 25(OH)D levels were sufficient. The levels of serum 25(OH)D₂ and 25(OH)D₃ were determined by liquid chromatography tandem mass spectrometry. The body composition was measured using dual-energy X-ray absorptiometry and corrected using body fat mass index (FMI). Based on the 100% difference in 25(OH)D levels before and after vitamin D supplementation, the sample size was calculated, and 20 subjects would provide over 95% of the power to show the difference.

Results

After two dose adjustment, the serum 25(OH)D levels of all subjects were above 30 ng/mL. The subjects were divided into ≤ 1,200,000 IU vitamin D₂ (n=10) and ≥ 2,400,000 IU vitamin D₂ (n=15) based on the i.m. dose of vitamin D₂. The results showed that compared with subjects receiving ≤ 1,200,000 IU vitamin D₂, subjects receiving ≥ 2,400,000 IU of vitamin D₂ had a higher total body fat mass index (FMI), particularly with higher trunk fat content and high visceral adipose tissue mass. However, the dosage of vitamin D₂ supplementation was not related to BMI and lean mass content.

Conclusion

The body fat content, especially trunk fat content, is the main body component that affects the bioavailability of vitamin D in healthy adults. Healthy adults with high trunk fat content have low bioavailability of vitamin D and require relatively high dose of vitamin D to achieve sufficient levels.

Clinical trial registration

http://www.chictr.org.cn, identifier ChiCTR2300070641.