Vitamin D levels after UVB radiation: effects by UVA additions in a randomized controlled trial.
Photodermatol Photoimmunol Photomed. 2013 Dec;29(6):323-9. doi: 10.1111/phpp.12076. Epub 2013 Oct 30.
Sallander E1, Wester U, Bengtsson E, Wiegleb Edström D.
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BACKGROUND: Ultraviolet B (UVB) radiation increases the serum level of 25-hydroxyvitamin D [25(OH)D]. However, the impact of UVA on vitamin D synthesis by UVB is poorly understood clinically.
OBJECTIVE: To examine how different combinations of UVA and UVB radiation affect S-25(OH)D for the same vitamin D-weighted exposure.
MATERIALS AND METHODS:
Healthy participants were recruited and subsequently divided into four comparable groups regarding initial 25(OH)D value. The different radiations given were whole-body UVB (n = 23), UVAB (n = 23) and UVA (n = 10). The controls (n = 19) had no intervention. The exposure times were chosen to give the same calculated vitamin D effective dose (suberythemal exposures ≤1 standard erythema dose). Blood samples were collected before the first irradiation (t0), immediately after the last (fifth) irradiation (t1) and then after another 2 days after the last (fifth) irradiation (t2).
RESULTS: UVB and UVAB radiation significantly increased 25(OH)D levels. In the UVA group the increase was less with the same vitamin D-weighted radiation dose.
Short sessions of UVB or UVAB radiation with the same vitamin D-weighted exposure increased 25(OH)D levels. The UVA dose does not influence 25(OH)D levels under short exposure times. However, there was a significantly lower increase of 25(OH)D levels during longer UVA irradiation (≥9 min).
Increased UVA exposures and decreased cutaneous Vitamin D(3) levels may be responsible for the increasing incidence of melanoma.
Med Hypotheses. 2009 Apr;72(4):434-43. Epub 2009 Jan 19.
Godar DE, Landry RJ, Lucas AD.
US Food and Drug Administration, Center for Devices and Radiological Health, 10903 New Hampshire Avenue (HFZ-120), Silver Spring, MD 20993-0002, USA. DEG at CDRH.FDA.GOV
Cutaneous malignant melanoma (CMM) has been increasing at a steady exponential rate in fair-skinned, indoor workers since before 1940. A paradox exists between indoor and outdoor workers because indoor workers get three to nine times less solar UV (290-400 nm) exposure than outdoor workers get, yet only indoor workers have an increasing incidence of CMM. Thus, another "factor(s)" is/are involved that increases the CMM risk for indoor workers.
We hypothesize that one factor involves indoor exposures to UVA (321-400 nm) passing through windows, which can cause mutations and can break down vitamin D(3) formed after outdoor UVB (290-320 nm) exposure, and the other factor involves low levels of cutaneous vitamin D(3). After vitamin D(3) forms, melanoma cells can convert it to the hormone, 1,25-dihydroxyvitamin D(3), or calcitriol, which causes growth inhibition and apoptotic cell death in vitro and in vivo. We measured the outdoor and indoor solar irradiances and found indoor solar UVA irradiances represent about 25% (or 5-10 W/m(2)) of the outdoor irradiances and are about 60 times greater than fluorescent light irradiances.
We calculated the outdoor and indoor UV contributions toward different biological endpoints by weighting the emission spectra by the action spectra: erythema, squamous cell carcinoma, melanoma (fish), and previtamin D(3). Furthermore, we found production of previtamin D(3) only occurs outside where there is enough UVB. We agree that intense, intermittent outdoor UV overexposures and sunburns initiate CMM; we now propose that increased UVA exposures and inadequately maintained cutaneous levels of vitamin D(3) promotes CMM. PMID: 19155143
Clipped from comment by Ted Hutchinson June 2011
"The UVA is helpful in creating previtamin d and in disposing of surplus D3(it converts unabsorbed D3 into suprasterols the body doesn't use) "
spend time in the sun then go indoors " . . the UVA only exposure would be degrading the vitamin D3 (it takes up to 48hrs to absorb) that remains near his skin surface. So often people think that 30~60mins sun exposure will be sufficient but then then drive home with the sun beating down on their skin through the car windows and by the time they get home the Vit D3 has all been safely converted to stuff the body doesn't use. "
getting sun in "...Town Centre and the reflection of UVA from walls windows and hard surfaces will amplify the UVA (uvb will be absorbed) so the ratio of vitamin d creating and vitamin d degrading UV will not be optimal. All urban dwellers make less D3 than do Rural dwellers. "
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