Although vitamin D supplementation effectively increased serum 25(OH)D concentrations, it did not reduce central adiposity among male shift workers.
Key Findings
Results
Cholecalciferol supplementation at either 14,000 IU/week or 28,000 IU/week for 4 months produced no significant effect on central adiposity outcomes compared to placebo.
Central adiposity was assessed by waist circumference (WC) and waist-to-height ratio (WHtR)
No significant differences in WC or WHtR were observed between either supplementation group and the placebo group (p > 0.05)
The trial was randomized, double-blind, and placebo-controlled with 198 male shift workers
Duration of intervention was 4 months
Results
Serum 25(OH)D concentrations increased significantly in both cholecalciferol supplementation groups.
The 14,000 IU/week group experienced an increase of +6.23 ng/mL (p25 = 0.58; p75 = 10.61)
The 28,000 IU/week group experienced an increase of +15.25 ng/mL (p25 = 10.57; p75 = 19.68)
The placebo group showed a decrease of -0.50 ng/mL (p25 = -1.03; p75 = 2.71)
Both supplementation groups showed statistically significant increases compared to placebo
Methods
The study enrolled male shift workers with both vitamin D insufficiency and at least one metabolic abnormality, representing a high-risk occupational population.
Participants were required to have 25(OH)D concentrations < 30 ng/mL
Eligible metabolic abnormalities included metabolic syndrome, impaired fasting glucose, dyslipidemia, elevated blood pressure, or increased waist circumference
All participants were male shift workers employed by an iron ore extraction company in Minas Gerais, Brazil
Total sample size was 198 participants randomized across three groups
Background
Shift workers are identified as a population at increased risk for both vitamin D deficiency and metabolic disorders.
The authors note that vitamin D deficiency is common among individuals with obesity
The association between low 25(OH)D concentrations and adiposity is described as 'unclear'
Shift workers were selected as a particularly relevant population for investigating the relationship between vitamin D and metabolic health
Conclusions
The authors conclude that vitamin D supplementation alone is unlikely to improve obesity-related outcomes in shift workers and that comprehensive strategies are needed.
Despite effective elevation of serum 25(OH)D, no reduction in central adiposity was observed
The authors underscore 'the need for comprehensive strategies targeting metabolic health in shift workers'
The findings suggest that vitamin D supplementation alone is insufficient to address metabolic outcomes in this high-risk occupational population
What This Means
This research suggests that taking vitamin D supplements does not reduce belly fat in male shift workers, even when the supplements successfully raise vitamin D levels in the blood. The study tested two doses of vitamin D (14,000 IU per week and 28,000 IU per week) against a placebo over four months in 198 male workers at an iron ore mine in Brazil. All participants started with low vitamin D levels and had at least one metabolic health problem such as high blood pressure, abnormal blood sugar, or high cholesterol. While both supplement doses raised vitamin D blood levels significantly compared to the placebo group, neither dose led to any meaningful reduction in waist circumference or waist-to-height ratio.
This research matters because shift workers are known to be at higher risk for both vitamin D deficiency and metabolic problems like obesity and diabetes, partly due to disrupted sleep schedules and reduced sunlight exposure. There has been ongoing interest in whether correcting vitamin D deficiency might help improve metabolic health, but this well-designed trial found no such benefit for central adiposity specifically. The higher dose produced a much larger increase in vitamin D levels (+15.25 ng/mL versus +6.23 ng/mL), yet neither dose moved the needle on waist measurements.
This research suggests that for shift workers struggling with excess belly fat and metabolic health issues, simply taking vitamin D supplements is unlikely to be sufficient. The authors emphasize that more comprehensive approaches — likely involving diet, exercise, and other lifestyle or medical interventions — are needed to address the metabolic risks faced by people who work non-standard hours.
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Menezes-Júnior L, Fajardo V, Oliveira F, Coelho G, Pimenta F, Nascimento Neto R, et al.. (2026). Vitamin D supplementation and central adiposity in male shift workers: a randomized clinical trial on metabolic health.. Sao Paulo medical journal = Revista paulista de medicina. https://doi.org/10.1590/1516-3180.2025.2955.18032026