Vitamin D production after UVB: aspects of UV-related and personal factors.

During the last decade vitamin D has become a hot topic and our knowledge of its vital role in health and disease is constantly expanding. Solar ultraviolet-B (UVB, 280-320 nm) is both the initiator of vitamin D production in the skin and a risk factor for sunburn and skin carcinogenesis. At present, this dilemma is debated worldwide. In Northern Europe, it is possible to reach a sufficient vitamin D status through sun exposure in the summer months. However, in the winter, the ambient UVB radiation is too low to initiate any production of vitamin D and this has led to a widespread concern and focus on vitamin D status. This review focuses on aspects of UV-related and personal factors of importance for the cutaneous vitamin D production after UVB exposure.

Vitamin D production depends on ultraviolet-B dose but not on dose rate: a randomized controlled trial.

Ultraviolet-B (UV-B) radiation increases serum vitamin D level expressed as 25-hydroxyvitamin D(3) (25(OH)D), but the dose-response relationship and the importance of dose rate is unclear. Of 172 fair-skinned persons screened for 25(OH)D, 55 with insufficient baseline 25(OH)D≤50 nm (mean 31.2 nm) were selected and randomized to one of 11 groups of five participants. Each group was exposed to one of four different UV-B doses: 0.375, 0.75, 1.5 or 3.0 standard erythema dose (SED) for 1, 5, 10 or 20 min. All participants had four UV-B sessions with 2- to 3-day interval with 24% of their skin exposed. Skin pigmentation and 25(OH)D were measured before and after the irradiations. The increase in 25(OH)D after UV-B exposure (adjusted for baseline 25(OH)D) was positively correlated with the UV-B dose (P=0.001; R(2) =0.176) but not to dose rate (1-20 min). 25(OH)D increased in response to four UV-B treatments of 3 SED with 24.8 nm on average and 14.2 nm after four UV-B treatments of just 0.375 SED. In conclusion, the increase in 25(OH)D after UV-B exposure depends on the dose but not on the dose rate (1-20 min). Further, a significant increase in 25(OH)D was achieved with a very low UV-B dose.

Vitamin D production after UVB exposure depends on baseline vitamin D and total cholesterol but not on skin pigmentation.

UVB radiation increases serum vitamin D level expressed as 25-hydroxyvitamin-D(3) (25(OH)D), but the influence of skin pigmentation, baseline 25(OH)D level, and total cholesterol has not been well characterized. To determine the importance of skin pigmentation, baseline 25(OH)D level, and total cholesterol on 25(OH)D production after UVB exposure, 182 persons were screened for 25(OH)D level. A total of 50 participants with a wide range in baseline 25(OH)D levels were selected to define the importance of baseline 25(OH)D level. Of these, 28 non-sun worshippers with limited past sun exposure were used to investigate the influence of skin pigmentation and baseline total cholesterol. The participants had 24% of their skin exposed to UVB (3 standard erythema doses) four times every second or third day. Skin pigmentation and 25(OH)D levels were measured before and after the irradiations. Total cholesterol was measured at baseline. The increase in 25(OH)D level after UVB exposure was negatively correlated with baseline 25(OH)D level (P<0.001) and positively correlated with baseline total cholesterol level (P=0.005), but no significant correlations were found with constitutive or facultative skin pigmentation. In addition, we paired a dark-skinned group with a fair-skinned group according to baseline 25(OH)D levels and found no differences in 25(OH)D increase after identical UVB exposure.