The D-lemma: narrow-band UV type B radiation versus vitamin D supplementation versus sunlight for cardiovascular and immune health

Abstract

In this issue of the Journal, Ponda et al. (1) report on the role of vitamin D and narrow-band UV type B (UVB) irradiation on the blood lipid profile of healthy adults. They previously observed that there was a relation between dyslipidemia and vitamin D status and that oral vitamin D 3 failed to provide any benefit in the lipid profile. They therefore explored the possibility that exposure to narrow-band UVB radiation might have a direct influence on blood cholesterol concentrations. In their previous observational study, they showed an association between LDL cholesterol and vitamin D status ) in the range of 5 mg/dL. In this study, for unclear reasons, they chose a goal of seeing a difference in LDL cholesterol of 9 mg/dL. This has important implications for the determination of sample size and the results. The lipid profile was noticeably different between the UVB group and the oral vitamin D 3 group (;2-fold), but the difference was not significant because of the small sample size. The small sample size and the many confounders such as different skin types, age, and baseline concentrations of LDL cholesterol were important limitations of this study. The observation that exposure to narrow-band UVB, which resulted in significant increases in circulating concentrations of 25(OH)D while having no effect on lipoprotein concentrations, confirms the observation by Carbone et al. (2).The connection between UVB radiation and cholesterol dates back to the 1920s, when it was first observed that the irradiation of cholesterol resulted in the production of the antirachitic factor vitamin D (3). Eventually, it was appreciated that cholesterol was stable to exposure to UVB radiation and that it was the tiny amount of its precursor, 7-dehydrocholesterol, which was present as a contaminant in the cholesterol preparation, that was sensitive to UVB radiation, resulting in its conversion to the antirachitic factor vitamin D. There was some consideration that because 7-dehydrocholesterol was the precursor of cholesterol, exposure to sunlight would reduce blood cholesterol concentrations because its precursor was being used. 7-Dehydrocholesterol is produced by the epidermal cells, and during exposure to sunlight only a tiny fraction, ,5%, is ever converted to previtamin D 3 (3). This is the reason why statins, which can lower blood cholesterol concentrations, have no influence on the cutaneous production of vitamin D 3 . The amount of 7-dehydrocholesterol and cholesterol in epidermal cells is independent of circulating concentrations of cholesterol.Ponda et al. (1) reported on 58 adults exposed to suberythemal doses of whole-body irradiation from lamps emitting narrowband UVB radiation 2 times/wk for $8 wk and showed no significant differences in the treated and controlled groups in any lipoproteins or apolipoproteins. What would have been helpful to have known is whether any of their subjects in their study were hypertensive and whether the narrow-band UVB radiation had any influence on their blood pressure?There have been a m...

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“…Human vitamin D metabolism involves multiple organ systems (Figure 1) [9], starting with conversion of 7-dehydrocholesterol (7DHC) to vitamin D within the epidermal layer of the skin. This reaction is catalysed by ultraviolet B with a wavelength of 290–315 nm [9,21,22]. Vitamin D then enters the circulation where it is rapidly 25-hydroxylated in the liver, where it remains as the storage form of vitamin D for several months.…”