Abstract
Vitamin D insufficiency/deficiency is prevalent worldwide. We investigated the effect of vitamin D intake and ultraviolet ray (UV) exposure on serum vitamin D concentration in Japan. A total of 107 healthy adult participants were recruited from Hokkaido (43° N) and Kumamoto (33° N) prefectures. All participants undertook surveys in both summer and winter. Serum 25-hydroxyvitamin D (25(OH)D3) was examined, and vitamin D intake was assessed with a diet history questionnaire. UV exposure was measured with a wearable UV dosimeter. Regression analysis was performed to investigate the relationship between these factors, with covariates such as sun avoidance behavior. The prevalence of vitamin D insufficiency (serum 25(OH)D3; 12 ng/mL (30 nmol/L) ≤ and <20 ng/mL (50 nmol/L))/deficiency (<12 ng/mL) was 47.7% in summer and 82.2% in winter. UV exposure time was short in Kumamoto (the urban area), at 11.6 min in summer and 14.9 min in winter. In Hokkaido (the rural area), UV exposure time was 58.3 min in summer and 22.5 min in winter. Vitamin D intake was significantly associated with serum 25(OH)D3, and a 1 μg/1000kcal increase in intake was necessary to increase 25(OH)D3 by 0.88 ng/mL in summer and by 1.7 ng/mL in winter. UV exposure time was significantly associated with serum 25(OH)D3 in summer, and a 10 min increase in UV exposure time was necessary to increase 25(OH)D3 by 0.47 ng/mL. Although consideration of personal occupation and lifestyle is necessary, most Japanese may need to increase both vitamin D intake and UV exposure.
Highlights
The fat-soluble vitamin D has two sources in humans—dietary intake and synthesis in the skin following exposure to ultraviolet B (UVB) radiation with wavelengths from 290 to 320 nm [1]
The lack of ultraviolet ray (UV) measurement tools has hampered efforts to estimate the effect of UV exposure on vitamin D status in the body, and reference values in several northern countries were established assuming that UVB exposure was minimal
Age was excluded from models 1time and 1energy to avoid over-adjustment, because it was positively and significantly associated with vitamin D intake and UV exposure
Summary
The fat-soluble vitamin D has two sources in humans—dietary intake and synthesis in the skin following exposure to ultraviolet B (UVB) radiation with wavelengths from 290 to 320 nm [1]. D has important functions in bone health [1], and several recent studies have investigated other positive health effects, including the prevention of cancer [2] and cardiovascular disease [3] Findings for these non-skeletal outcomes remain inconclusive, and current dietary recommendations for vitamin D have been designed to maintain serum 25-hydroxyvitamin D (25(OH)D) at concentrations sufficient to maintain healthy bones [1]. In Japan, a reference value called “adequate intake (AI)” has been established [10], assuming that a proportion of vitamin D comes from cutaneous synthesis. This value is set when there is insufficient evidence to establish firmer indexes, such as estimated average requirements and recommended dietary allowance.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
