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Ultraviolet-B radiation increases serum 25-hydroxyvitamin D levels: The effect of UVB dose and skin color

https://doi.org/10.1016/j.jaad.2007.03.004Get rights and content

Background

Ultraviolet (UV)-B light increases vitamin D levels, but the dose response and the effect of skin pigmentation have not been well characterized.

Objective

We sought to define the relationship between UVB exposure and 25-hydroxyvitamin D (25-OH-D) concentrations as a function of skin pigmentation.

Methods

Seventy two participants with various skin tones had 90% of their skin exposed to UVB light (20-80 mJ/cm2) 3 times a week for 4 weeks. Serum 25-OH-D was measured weekly.

Results

Eighty percent of the variation in treatment response was explained by UVB dose and skin tone. Therapeutically important changes in 25-OH-D were achieved with minimal tanning.

Limitations

Four weeks was not long enough to reach a steady state at the higher dose rates.

Conclusions

The response of 25-OH-D levels to UVB light is dependent on skin pigmentation and the amount of UVB given, and useful increases in vitamin D status can be achieved by defined UVB doses small enough to produce only minimal tanning.

Section snippets

Participants

We recruited 77 participants. Of the 72 who completed the study, there were 42 women and 30 men; ages ranged between 19 and 49 years (Table I). They were in good general health, habitually consumed less than 0.47 L (16 oz) of milk per day, and had less than 10 hours of sun exposure per week during the study period. We gathered information on vitamin supplement use and milk intake by questionnaire. We excluded those with granulomatous conditions, liver disease, kidney disease, thyroid disease,

Baseline characteristics

Pertinent personal and biochemical characteristics are set forth in Table I. Of most pertinence to this investigation, baseline serum 25-OH-D ranged from 6.8 to 48.5 ng/mL (17-121 nmol/L) and L values from 36.4 to 71.7 for unexposed skin. A typical northern European person would have an L value for unexposed skin of about 70; a sub-Saharan African would have an L value of about 35; and an African American would have an L value of about 50. There was a significant positive correlation

Discussion

Although it has been known for some time that individuals with dark skin tend to have lower vitamin D status than those with lighter skin16, 17 this is, to our knowledge, the first study reported in the literature quantifying the relationship, using an objective measure of skin pigmentation, and incorporating both basal vitamin D status and response to UVB radiation.

As have many others,16, 18, 19 we noted a marked seasonal difference in baseline 25-OH-D levels between those participants who

References (23)

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      Nevertheless, circannual variation of vitamin D status in CKD stage 5 or dialysis patients with higher concentrations in the summer than winter time has been previously described [36–39]. In our study, we did not see a modification of the amplitude of seasonal variation by the yearly average of each month's SD of UVI, which was unexpected since the association between UVB radiation and 25(OH)D concentrations has been well established [3,40–43]. However, vitamin D supplementation might mask the relationship between UVI and 25(OH)D concentration [34], or ESRD patients might be less physically active [44] and therefore have less exposure to UVB radiation.

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    Supported by Dialysis Clinics Inc, The Endocrine Fellows Foundation, and research funds of Creighton University.

    Disclosure: Dr Hollis is a consultant for Diasorin. Diasorin manufactures assays for 25-hydroxyvitamin D. Drs Armas, Dowell, Akhter, Duthuluru, Huerter, Lund, and Heaney have no conflicts of interest to declare.

    Reprints not available from the authors.

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