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In vivo threshold for cutaneous synthesis of vitamin D3. Matsuoka LY, Wortsman J, Haddad JG, Hollis BW. J Lab Clin Med. 1989 Sep;114(3):301-5. PMID: 2549141

Global vitamin D status and determinants of hypovitaminosis D. Mithal A, Wahl DA, Bonjour JP, Burckhardt P, Dawson-Hughes B, Eisman JA, El-Hajj Fuleihan G, Josse RG, Lips P, Morales-Torres J; on behalf of the IOF Committee of Scientific Advisors (CSA) Nutrition Working Group. Osteoporos Int. 2009 Jun 19. [Epub ahead of print] PMID: 19543765 CONCLUSION: Reports from across the world indicate that hypovitaminosis D is widespread and is re-emerging as a major health problem globally.

Can vitamin D supplementation prevent winter-time blues? A randomised trial among older women. Dumville JC, Miles JN, Porthouse J, Cockayne S, Saxon L, King C. J Nutr Health Aging. 2006 Mar-Apr;10(2):151-3. PMID: 16554952 CONCLUSIONS: Supplementing elderly women with 800 IU of vitamin D daily did not lead to an improvement in mental health scores.

Vitamin D and skin physiology: a D-lightful story.\nHolick MF, Chen TC, Lu Z, Sauter E.\nJ Bone Miner Res. 2007 Dec;22 Suppl 2:V28-33.\nPMID: 18290718 \ndoi: 10.1359/jbmr.07s211\n

Vitamin D production in human skin occurs only when UV radiation exceeds a threshold. From simulations of UV irradiances, the VitD www page ( http://zardoz.nilu.no/~olaeng/fastrt/VitD.html) computes the daily duration of dermal vitamin D production at midday when UV radiation exceeds the required threshold. The daily duration depends on latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude all of which can be specified by the user

Chen TC, Chimeh F, Lu Z, Mathieu J, Person KS, Zhang A, Kohn N, Martinello S, Berkowitz R, Holick MF. Factors that influence the cutaneous synthesis and dietary sources of vitamin D. Arch Biochem Biophys. 2007 Apr 15;460(2):213-7. Epub 2007 Jan 8. PMI

Ultraviolet exposure scenarios: risks of erythema from recommendations on cutaneous vitamin D synthesis. Webb AR, Engelsen O. Adv Exp Med Biol. 2008;624:72-85. PMID: 18348448 DOI: 10.1007/978-0-387-77574-6_6

Vitamin D production in human skin occurs only when UV radiation exceeds a threshold. From simulations of UV irradiances, the VitD-ez www page ( http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html) computes the daily duration of dermal vitamin D production at midday when UV radiation exceeds the required threshold. The VitD-ez www page is a simplified version of the more complex VitD web page ( http://zardoz.nilu.no/~olaeng/fastrt/VitD.html). The simplified VitD-ez www page is convenient for users unfamiliar to radiative transfer modelling, because the model input is limited and more intuitive.

Daily duration of vitamin D synthesis in human skin with relation to latitude, total ozone, altitude, ground cover, aerosols and cloud thickness. Engelsen O, Brustad M, Aksnes L, Lund E. Photochem Photobiol. 2005 Nov-Dec;81(6):1287-90. PMID: 16354110 Vitamin D production in human skin occurs only when incident UV radiation exceeds a certain threshold. From simulations of UV irradiances worldwide and throughout the year, we have studied the dependency of the extent and duration of cutaneous vitamin D production in terms of latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude. For clear atmospheric conditions, no cutaneous vitamin D production occurs at 51 degrees latitude and higher during some periods of the year. At 70 degrees latitude, vitamin D synthesis can be absent for 5 months. Clouds, aerosols and thick ozone events reduce the duration of vitamin D synthesis considerably, and can suppress vitamin D synthesis completely even at the equator. A web page allowing the computation of the duration of cutaneous vitamin D production worldwide throughout the year, for various atmospheric and surface conditions, is available on the Internet at http://zardoz.nilu.no/~olaeng/fastrt/VitD.html and http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html. The computational methodology is outlined here.

sunlightD.org Grassroots Health and ZRT Labs are working together to help us all make sure we have enough vitamin D. Participate in understanding vitamin D. Visit grassrootshealth.net and join the research project. You'll get your D tested twice a year for five years. The cost is just $40 a test, $80 a year, more than reasonable for accurate D testing, and you'll help provide real answers, for yourself and for us all, about how much D we get and how much we need. Join now. Do commit to the full 5 years if you decide to sign on. If not joining for the full test period please use the testing links below.