Efficacy of a dose range of simulated sunlight exposures in raising vitamin D status in South Asian adults:
implications for targeted guidance on sun exposure.
Am J Clin Nutr. 2013 Apr 24.
Farrar MD, Webb AR, Kift R, Durkin MT, Allan D, Herbert A, Berry JL, Rhodes LE.
Dermatology Centre, Institute of Inflammation and Repair, University of Manchester, Manchester Academic Health Science Centre, Salford Royal National Health Service Foundation Trust, Manchester, United Kingdom.
BACKGROUND: Vitamin D is essential for bone health, and cutaneous synthesis is an important source. South Asians cannot attain adequate amounts of vitamin D by following general recommendations on summer sunlight exposure at northerly latitudes, and increased exposure may be appropriate for improving their vitamin D status.
OBJECTIVE: We examined the efficacy of a dose range of simulated summer sunlight exposures in raising vitamin D status in UK adults of South Asian ethnicity.
DESIGN: In a dose-response study, healthy adults of South Asian ethnicity (n = 60; 20-60 y old) received 1 of 6 ultraviolet exposures ranging from 0.65 to 3.9 standard erythema doses (SEDs), which were equivalent to 15-90 min unshaded noontime summer sunlight at 53.5°N (Manchester, United Kingdom), 3 times/wk for 6 wk, while wearing casual clothes that revealed a 35% skin area. Serum 25-hydroxyvitamin D [25(OH)D] was measured weekly, and dietary vitamin D was estimated.
RESULTS: At baseline, all completing participants (n = 51) were vitamin D insufficient [25(OH)D concentrations <20 ng/mL], and a high proportion of participants were deficient [35% of subjects had 25(OH)D concentrations <5 ng/mL, and 90% of subjects had 25(OH)D concentrations <10 ng/mL, which are concentrations at which osteomalacia and rickets occur). The 25(OH)D concentration rose significantly in all dose groups. Postcourse, all participants achieved 25(OH)D concentrations ≥5 ng/mL, whereas only 6 subjects attained 25(OH)D concentrations ≥20 ng/mL.
Participants who received exposures ≥1.95 SEDs (equivalent to 45 min unshaded sunlight; n = 33) attained a mean (±SD) 25(OH)D concentration of 15.7 ± 5 ng/mL (mean rise: 8.7 ± 5.7 ng/mL; 95% CI: 6.8, 10.6; P < 0.001), and 94% of subjects achieved concentrations >10 ng/mL.
CONCLUSIONS: Targeted guidance on sunlight exposure could usefully enhance vitamin D status to avoid deficiency [[25(OH)D concentration >10 ng/mL] in South Asians living at latitudes distant from the equator. This trial was registered at the ISRCTN Register (www.isrctn.org) as 07565297.
- SE Asian women getting 23+ minutes summer sun per day in UK
- Casual clothes that revealed a 35% skin area
- Mean vitamin D level 16 ng (low)
- 94% were >10 ng
Like most chemical reactions, more vitamin D is generated at higher temperatures
The skin is probably hotter in the sun than in the tanning bed
See: Factors (including skin temperature) Influencing Vitamin D Status – 2011
- No – 10 minutes per day of sun-UVB is NOT enough
- 60 minutes of sunlight needed to decrease vitamin D deficiency in sunny climate – Dec 2012
- Study of vitamin D level vs hours in the sun, etc. – Feb 2013
- 80 percent of South Asian Women in UK had less than 10 ng of vitamin D in winter – April 2012
- Immigrant vitamin D deficiency in Europe – May 2011
- Vitamin D insufficiency in UK youths – 37X more likely if dark skin – July 2011
- Schizophrenia high and increasing in Canada – lower vitamin D and more dark skin – Feb 2013
- Dark skinned pregnant women far from equator were very vitamin D deficient – Sept 2012
- Dark skin does not generate as much vitamin D from the same amount of UV – Nov 2011