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Vitamin D levels remain acceptable for a few months into the winter – Feb 2015

Limited exposure to ambient ultraviolet radiation and 25-hydroxyvitamin D levels: a systematic review.

Br J Dermatol. 2015 Feb 3. doi: 10.1111/bjd.13575. [Epub ahead of print]
Rice SA1, Carpenter M, Fityan A, Vearncombe LM, Ardern-Jones M, Jackson AA, Cooper C, Baird J, Healy E.
1Dermatopharmacology, Sir Henry Wellcome Laboratories, Faculty of Medicine, University of Southampton, Southampton General Hospital, Tremona Road, Southampton, SO16 6YD, U.K.

Vitamin D can be synthesized following exposure to ultraviolet radiation (UVR), ingested in the diet or provided through oral supplementation. The medical literature frequently states that humans obtain most of their vitamin D from sunshine and that UVR exposure is essential to maintain vitamin D levels. A systematic review was conducted to determine the requirement for UVR in maintaining adequate (> 50 nmol L-1 ) serum 25-hydroxyvitamin D [25(OH)D] levels. Studies reporting serum 25(OH)D during situations of negligible UVR exposure were sought.
Forty-one studies (from a search yielding 42 698 articles) with a total of 4211 healthy adults met the inclusion criteria, providing 56 datasets from different population groups.

  • Over 50% of subjects had > 50 nmol L-1 25(OH)D in 10 of 19 datasets reporting winter levels in areas with limited UVR.
  • In addition, > 50% of subjects had adequate 25(OH)D levels in
    four of 12 datasets from polar regions during periods of negligible UVR,
    one of nine datasets documenting clothing-related minimal UVR and
    two of eight datasets detailing employment-related minimal UVR.

The data demonstrate that many adults maintain adequate serum vitamin D levels despite negligible UVR exposure for several months. However, we acknowledge that preceding UVR exposure leading to vitamin D storage and delayed release may account for this maintenance of adequate serum vitamin D levels. There remains a need for further research on whether UVR exposure is required for longer-term maintenance of adequate vitamin D levels.

© 2015 British Association of Dermatologists
which might have a free PDF - not online as of Feb 4, 2015

PMID: 25646772

See also VitaminDWiki

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