The Solar Exposure Time Required for Vitamin D3 Synthesis in the Human Body Estimated by Numerical Simulation and Observation in Japan

Abstract

Although the importance of solar radiation for vitamin D3 synthesis in the human body is well known, the solar exposure time required to prevent vitamin D deficiency has not been determined in Japan. This study attempted to identify the time of solar exposure required for vitamin D3 synthesis in the body by season, time of day, and geographic location (Sapporo, Tsukuba, and Naha) using both numerical simulations and observations. According to the numerical simulation for Tsukuba at noon in July under a cloudless sky, 3.5 min of solar exposure are required to produce 5.5 μg vitamin D3 per 600 cm2 skin corresponding to the area of a face and the back of a pair of hands without ingestion from foods. In contrast, it took 76.4 min to produce the same quantity of vitamin D3 at Sapporo in December, at noon under a cloudless sky. The necessary exposure time varied considerably with the time of the day. For Tsukuba at noon in December, 22.4 min were required, but 106.0 min were required at 09:00 and 271.3 min were required at 15:00 for the same meteorological conditions. Naha receives high levels of ultraviolet radiation allowing vitamin D3 synthesis almost throughout the year.

Seasonal variations in vitamin D status in indoor and outdoor female athletes

“…The length of solar exposure required to synthesize 5.5 µg of VD in the middle of Japan was reported as 20 min at any time of the day in summer and early autumn (May to September), but >1 h in the morning/evening from November to March (21). The middle of Japan, in the report to estimate solar exposure (21), was within 50 km from the campus conducting the present study.…”

“…The middle of Japan, in the report to estimate solar exposure (21), was within 50 km from the campus conducting the present study. Thus, a similar estimation should be applicable to the present subjects.…”

Decreased serum vitamin D levels in Japanese patients with multiple sclerosis

“…We also compared winter serum vitamin D levels between patient populations living in the northern or southern region of Japan because it was reported that there is a significant difference in solar radiation between north and south Japan, particularly during winter (Miyauchi et al, 2013). Furthermore, as a study from the Netherlands reported that low serum 25(OH)D was associated with higher Expanded Disability Status Scale (EDSS) scores (Smolders et al, 2008), we examined the association of vitamin D with disability level and disease progression in the same patient population.…”

The angular distributions of ultraviolet spectral irradiance at different solar elevation angles under clear sky conditions

“…Seckmeyer et al (2013) used a mathematical method to calculate vitD-weighted exposure via integration of the incident solar spectral irradiance over all relevant parts of the human body. Miyauchi et al (2013) used a numeric model to estimate the solar time required for vitD synthesis in the human body and observed locations in Japan to verify the model.…”