Work

25-Hydroxyvitamin D3 metabolism modulates the effect of variable UV exposure on 25-hydroxyvitamin D3 plasma concentrations

Year: 2026

Type: article

Abstract: 25-hydroxyvitamin D3 (25(OH)D3) affects immune function, bone health, and reproduction. The precursor of 25(OH)D3, vitamin D3, is synthesized upon ultraviolet (UV) radiation exposure, the levels of which vary. In a one-year observational study, we used multiple statistical approaches to examine 25(OH)D3 metabolism and UV exposure in 217 healthy men (aged 30–50 years) not using vitamin D supplementation, living between Athens and the Arctic Circle. Complementary data were obtained from six consecutive crews of Antarctic expeditioners. We show that, while vitamin D3 synthesis tracks UV exposure, resulting 25(OH)D3 concentrations are strongly shaped by the kinetics of 25(OH)D3 synthesis and degradation. Notably, the efficiency of 25(OH)D3 synthesis is high at low vitamin D3, but decreases markedly at higher vitamin D3. This results in comparable summer 25(OH)D3 maxima across European sites. Additionally, the kinetics of 25(OH)D3 degradation induces rapid seasonal concentration shifts, yet also exerts a moderating effect by dampening both seasonal maximum and minimum 25(OH)D3. Comparison of the seasonal patterns of plasma parameters and environmental parameters at European sites shows that vitamin D3 follows the UV exposure pattern, while 25(OH)D3 concentrations align with local temperature patterns. Antarctic data support the alignment between 25(OH)D concentrations and temperature. The kinetics of 25(OH)D3 synthesis and degradation modulate the effect of variable UV exposure on 25(OH)D3 concentrations. This results in a regulated plasma signal reflecting local seasonal parameters. While absolute 25(OH)D3 concentrations are commonly investigated, future studies should also examine their temporal dynamics as a biological signal. Our study explored how the human body manages different levels of sunlight with respect to the primary form of vitamin D measured in blood tests. Vitamin D is important for bone strength, immune function, and other health effects, and it is produced in the skin when exposed to sunlight. This study followed 217 healthy men living in different parts of Europe over the course of a year. We found that while sunlight triggers vitamin D production, the body also influences vitamin D levels through how it builds up and breaks down this substance over time. These findings help us understand how vitamin D levels are naturally regulated and may improve how we protect and support health through vitamin D. Scholze et al. investigate individual UV exposure and 25(OH)D3 metabolism in a one-year observational study. While UV exposure triggers vitamin D3 production, the body strongly modulates the resulting 25(OH)D3 concentrations through 25(OH)D3 synthesis efficiency and degradation, with the seasonal pattern mirroring local temperature fluctuations.

Source: Communications Medicine

DOI: 10.1038/s43856-025-01368-7