Group items tagged

Aging decreases the capacity of human skin to produce vitamin D3. MacLaughlin J, Holick MF. J Clin Invest. 1985 Oct;76(4):1536-8. PMID: 2997282 doi:10.1172/JCI112134 An evaluation of surgically obtained skin (age range, 8-92 yr) revealed that there is an age-dependent decrease in the epidermal concentrations of provitamin D3 (7-dehydrocholesterol). To ascertain that aging indeed decreased the capacity of human skin to produce vitamin D3, some of the skin samples were exposed to ultraviolet radiation and the content of previtamin D3 was determined in the epidermis and dermis. The epidermis in the young and older subjects was the major site for the formation of previtamin D3, accounting for greater than 80% of the total previtamin D3 that was produced in the skin. A comparison of the amount of previtamin D3 produced in the skin from the 8- and 18-yr-old subjects with the amount produced in the skin from the 77- and 82-yr-old subjects revealed that aging can decrease by greater than twofold the capacity of the skin to produce previtamin D3. Recognition of this difference may be extremely important for the elderly, who infrequently expose a small area of skin to sunlight and who depend on this exposure for their vitamin D nutritional needs.

White Europeans could have evolved as recently as 5,500 years ago, according to research which suggests that the early humans who populated Britain and Scandinavia had dark skins for millenniums. It was only when early humans gave up hunter-gathering and switched to farming about 5,500 years ago that white skin began to be favoured, say the researchers. This is because farmed food was deficient in vitamin D, a vital nutrient. Humans can make this in their skin when exposed to sunlight, but dark skin is much less efficient at it.

Robert P. Heaney is John A. Creighton University Professor, Creighton University, Omaha, Nebraska, United States. Hominid evolution took place in an environment (equatorial East Africa) that provided a superabundance of both calcium and vitamin D, the first in available foods and the second through conversion of 7-dehydrocholesterol to pre-vitamin D in the skin, a reaction catalysed by the intense solar ultraviolet (UV) radiation. Seemingly as a consequence, the evolving human physiology incorporated provisions to prevent the potential of toxic excesses of both nutrients. For vitamin D the protection was of two sorts: skin pigmentation absorbed the critical UV wavelengths and thereby limited dermal synthesis of cholecalciferol; and slow delivery of vitamin D from the skin into the bloodstream left surplus vitamin in the skin, where continuing sun exposure led to its photolytic degradation to inert compounds. For calcium, the adaptation consisted of very inefficient calcium absorption, together with poor to absent systemic conservation. The latter is reflected in unregulated dermal calcium losses, a high sensitivity of renal obligatory calcium loss to other nutrients in the diet and relatively high quantities of calcium in the digestive secretions. Today, chimpanzees in the original hominid habitat have diets with calcium nutrient densities in the range of 2 to 2.5 mmol per 100 kcal, and hunter-gatherer humans in Africa, South America and New Guinea still have diets very nearly as high in calcium (1.75 to 2 mmol per 100 kcal) (Eaton and Nelson, 1991). With energy expenditure of 3 000 kcal per day (a fairly conservative estimate for a contemporary human doing physical work), such diets would provide substantially in excess of 50 mmol of calcium per day. By contrast, median intake in women in North America and in many European countries today is under 15 mmol per day. Two factors altered the primitive situation: the migration of humans from Africa to higher latitude

October 6th, 2008 A study led by researchers at the University of California, San Diego School of Medicine suggests that use of oral Vitamin D supplements bolsters production of a protective chemical normally found in the skin, and may help prevent skin infections that are a common result of atopic dermatitis, the most common form of eczema.

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.

Holick, M. F., MacLaughlin, J. A. & Doppelt, S. H. (1981) Factors that influence the cutaneous photosynthesis of previtamin D3. Science 211:590-593 When human skin was exposed to simulated solar ultraviolet radiation, epidermal 7-dehydrocholesterol was converted to previtamin D3. During prolonged exposure to simulated solar ultraviolet radiation, the synthesis of previtamin D3 reached a plateau at about 10 to 15 percent of the original 7-dehydrocholesterol content, and previtamin D3 was photoisomerized to two biologically inert isomers, lumisterol3 and tachysterol3. Increases either in skin melanin concentration or in latitude necessitated increases in the exposure time to simulated solar ultraviolet radiation required to maximize the formation, but not the total content, of previtamin D3. In order of importance, the significant determinants limiting the cutaneous production of previtamin D3 are (i) photochemical regulation, (ii) pigmentation, and (iii) latitude.

Sweat gland epithelial and myoepithelial cells are vitamin D targets. Koike N, Stumpf WE. Exp Dermatol. 2007 Feb;16(2):94-7. PMID: 17222221 DOI: 10.1111/j.1600-0625.2006.00513.x Nuclear receptor binding of 1,25(OH)2-vitamin D3 (vitamin D) in skin keratinocytes of epidermis, hair sheaths and sebaceous glands was discovered through receptor microscopic autoradiography. Extended experiments with 3H-1,25(OH)2-vitamin D3 and its analog 3H-oxacalcitriol (OCT) now demonstrate nuclear receptor binding in sweat gland epithelium of secretory coils and ducts as well as in myoepithelial cells, as studied in paws of nude mice after i.v. injection. The results suggest genomic regulation of cell proliferation and differentiation, as well as of secretory and excretory functions, indicating potential therapies for impaired secretion as in hypohidrosis of aged and diseased skin.

Aging decreases the capacity of human skin to produce vitamin D3. MacLaughlin J, Holick MF. J Clin Invest. 1985 Oct;76(4):1536-8. PMID: 2997282

nfluence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. Webb AR, Kline L, Holick MF. J Clin Endocrinol Metab. 1988 Aug;67(2):373-8. PMID: 2839537 doi:10.1210/jcem-67-2-373 These results quantify the dramatic influence of changes in solar UVB radiation on cutaneous vitamin D3 synthesis and indicate the latitudinal increase in the length of the "vitamin D winter" during which dietary supplementation of the vitamin may be advisable.

Vitamin D and skin physiology: a D-lightful story. Holick MF, Chen TC, Lu Z, Sauter E. J Bone Miner Res. 2007 Dec;22 Suppl 2:V28-33. PMID: 18290718 doi: 10.1359/jbmr.07s211 Very few foods naturally contain vitamin D, and those that do have a very variable vitamin D content. Recently it was observed that wild caught salmon had between 75% and 90% more vitamin D(3) compared with farmed salmon. The associations regarding increased risk of common deadly cancers, autoimmune diseases, infectious diseases, and cardiovascular disease with living at higher latitudes and being prone to vitamin D deficiency should alert all health care professionals about the importance of vitamin D for overall health and well being. Humans have depended on sunlight for their vitamin D requirement. The impact of season, time of day, and latitude on vitamin D synthesis is well documented.(2,3) We now report that altitude also has a dramatic influence on vitamin D3 production and that living at altitudes above 3500 m permits previtamin D3 production at a time when very little is produced at latitudes below 3400 m. It was surprising that, at 27° N in Agra (169 M), little previtamin D3 production was observed. However, there was significant air pollution that caused a haze over the city. It is likely the ozone and other UVB-absorbing pollutants in the air prevented the solar UVB photons from reaching the earth's surface to produce previtamin D3.

Vitamin D: In the evolution of human skin colour. Yuen AW, Jablonski NG. Med Hypotheses. 2009 Aug 28. [Epub ahead of print] PMID: 19717244

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

Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure.\nMoan J, Porojnicu AC, Dahlback A, Setlow RB.\nProc Natl Acad Sci U S A. 2008 Jan 15;105(2):668-73. Epub 2008 Jan 7.\nPMID: 18180454

Vitamin D is a fat-soluble vitamin that is essential for maintaining normal calcium metabolism (1). Vitamin D3 (cholecalciferol) can be synthesized by humans in the skin upon exposure to ultraviolet-B (UVB) radiation from sunlight, or it can be obtained from the diet. Plants synthesize ergosterol, which is converted to vitamin D2 (ergocalciferol) by ultraviolet light. Vitamin D2 is less active in birds than vitamin D3 and may also be less active in humans (2). When exposure to UVB radiation is insufficient for the synthesis of adequate amounts of vitamin D3 in the skin, adequate intake of vitamin D from the diet is essential for health.

Diagnosis and treatment of vitamin D deficiency. Cannell JJ, Hollis BW, Zasloff M, Heaney RP. Expert Opin Pharmacother. 2008 Jan;9(1):107-18. PMID: 18076342 The recent discovery - in a randomised, controlled trial - that daily ingestion of 1100 IU of colecalciferol (vitamin D) over a 4-year period dramatically reduced the incidence of non-skin cancers makes it difficult to overstate the potential medical, social and economic implications of treating vitamin D deficiency. Not only are such deficiencies common, probably the rule, vitamin D deficiency stands implicated in a host of diseases other than cancer. The metabolic product of vitamin D is a potent, pleiotropic, repair and maintenance, secosteroid hormone that targets > 200 human genes in a wide variety of tissues, meaning it has as many mechanisms of action as genes it targets. A common misconception is that government agencies designed present intake recommendations to prevent or treat vitamin D deficiency. They did not. Instead, they are guidelines to prevent particular metabolic bone diseases. Official recommendations were never designed and are not effective in preventing or treating vitamin D deficiency and in no way limit the freedom of the physician - or responsibility - to do so. At this time, assessing serum 25-hydroxy-vitamin D is the only way to make the diagnosis and to assure that treatment is adequate and safe. The authors believe that treatment should be sufficient to maintain levels found in humans living naturally in a sun-rich environment, that is, > 40 ng/ml, year around. Three treatment modalities exist: sunlight, artificial ultraviolet B radiation or supplementation. All treatment modalities have their potential risks and benefits. Benefits of all treatment modalities outweigh potential risks and greatly outweigh the risk of no treatment. As a prolonged 'vitamin D winter', centred on the winter solstice, occurs at many temperate latitudes, ≤ 5000 IU (125 μg) of vitamin D/d

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.