1. Describe the role of vitamin D and folic acid and also th by Brightyn and Em on Prezi
May 16, The Inuit's are dark-skinned despite the lack of sunlight in the subarctic region. They do not need lighter skin to ensure Vitamin D production. The relationship between Vitamin D, folate, melanin, and sunshine are compared to a sequence of events that triggers one another. For example, when a person. Mar 21, Folic acid is a B vitamin that is very important for pregnant women and found high levels of sun exposure reduce folate in young women. Dr Borradale said in showing the link between UV exposure and folate depletion.
Desirable vitamin D doses and erythemal doses are more similar for low solar elevations. Acknowledgements The author would like to thank Ann Webb, University of Manchester for valuable input to this review paper. Notes Added in Proof In the first paragraph of section 3 I state that "The lamp spectral characteristics are unclear, and assimilation to natural conditions is difficult due to uncertainties in vitamin D action spectrum. These results will improve simulation model 2 in section 5.
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UVR, vitamin D and three autoimmune diseases-multiple sclerosis, type 1 diabetes, rheumatoid arthritis. Vitamin D status and arterial hypertension: Vitamin D for treatment and prevention of infectious diseases: Toll-Like receptor triggering of a vitamin D-Mediated human antimicrobial response.
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Skin color & Vitamin D & folate - Gene Expression
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ISBN 3 50 9. Effects of clouds and haze on UV-B radiation. Five years of cloud enhanced surface UV radiation measurements at two sites in the Northern and Southern Hemispheres Atm. The ultraviolet cross-sections of ozone, I, The measurements. Solar UVB-Albedo of various surfaces. Chronic sunscreen use decreases circulating concentrations of hydroxyvitamin D. Use of topical sunscreen for the evaluation of regional synthesis of vitamin D3. Vitamin D effective ultraviolet wavelengths due to scattering in shade.
The validity and practicality of sun-reactive skin types I through VI. Increased skin pigment reduces the capacity of skin to synthesise vitamin D3. Indian and Pakistani immigrants have the same capacity as Caucasians to produce vitamin D in response to ultraviolet radiation. The end result of this is reduced folate levels, which in pregnant females often causes neural tube abnormalities.
Any impact on pregnancy success is an extremely powerful selective force. In this model the dark skin of humans naturally arose because women who were darker skinned carried more normal fetuses to term than those who were light skinned. In dark skinned populations the MC1R locus is extremely conserved, suggesting powerful selective constraints which prevent sequence variation.
No matter the phylogenetic relationships between dark skinned populations there is a consensus sequence which seems to have been selected for deep in the human past which remains the norm across these groups i. But counterbalancing the need to block sunlight due to reduction in folate levels is the fact that vitamin D synthesis requires a minimum level of radiation to be catalyzed.
Reduced vitamin D levels not only result in bone deformations i. The map to the left is a rough sketch of variation in skin color throughout the world. This means that melanin pigement concentrations need not be as dense to protect the folic acid synthesis pathway from degradation. And, the reduced density of melanin maybe necessary for vitamin D levels to be maintained due to the essential role of radiation in catalyzing its production.
In short, as one moves away from the tropics the selective constraint to maintain high folate levels by blocking UV via dark skin is removed, while a countervailing pressure to reduce the density of melanin so as to allow enough radiation to stimulate vitamin D synthesis emerges. In Scandinavia the Sami are darker than the peoples to the south, and the Inuit are generally a light brown skinned people. It seems that the fairest peoples in the world reside around the shores of the Baltic sea, not in the circumpolar regions.
The fact that I eat a relatively rich diet and do expose myself to the sun when I can, but still exhibit vitamin D deficiency, brought home to me the dependence upon nutritional parameters as well as skin color. Though agricultural peoples are efficient at reproduction and natural increase because of the high yields they can extract from the land via intensive farming, they have generally had to deal with the trade off that their diet became reliant on starches which were poor in many vital nutrients as well as proteins.
Human have become smaller over the last 10, years, and the contrast between the relatively healthy skeletons of hunter-gatherers and the physiological stress exhibited by the farmers which succeeded them have long been noted. Recently work in genomics also suggests genes implicated in various metabolic functions have been under powerful selection over the past 10, years as the agricultural lifestyle has spread.
The deleterious consequences of switching many non-agricultural populations to the starch rich diet are well known obesity, diabetes, etc. Selection happens, and it seems likely that a genetic revolution was ushered in by the radically altered nutritional universe of the farmer.
Which brings me to Europeans and why they might be so light. Sweet published an essay in which offered that the feasibility of a farming lifestyle at very high latitudes in Europe due to peculiar climatological conditions served to drive Europeans to develop light skins over the last 10, years.
In short, Sweet argues that the diets of pre-farming peoples were richer in meats and fish which provided sufficient Vitamin D so that skin color was likely light brown as opposed to pink.
But with the spread of agriculture Vitamin D disappeared from the diets of northern European peoples and so only by reducing their melanin levels could they produce sufficient amounts of this nutrient to keep at bay the deleterious consequences of deficiencies. This explains why the Sami, who never adopted agriculture, remained darker. One could hypothesize that the relative swarthiness of groups like the Welsh might be due to greater reliance on fish and game as opposed to agriculture, but the point is not to explain every last detail but to clarify the overall trend.
It seems that on this locus the two populations were disjoint, they exhibited no substantial overlap. In European it seems that 6 to 10 thousand years ago a new variant arose which subsequently swept to fixation. But, it seems that other loci are responsible for the lightening of the skin of East Asians recently as well, though not to the same extent as Europeans.
The Relationship between Ultraviolet Radiation Exposure and Vitamin D Status
The reason for this is likely the fact that temperate East Asia as at a far lower latitude than Europe. Of course, there are other anomalies. Sweet points out that South Americans are far paler than they should be if Old World populations are to be any judge.
His explanation is simple: There are two parameters which might explain the relative lightness or darkness and overall homogeneity of New World populations. Rather, the bigger problem was likely that extant genetic variation was reduced by a population bottleneck. Over time this variation would be replenished by mutation, but this is a slow process.
This suggests evolutionary lag on many characteristics due to the low genetic diversity combined with the particular time frame over which evolution could occur but even here, do note that there is a skin color gradation from the tropics to the temperate zones in the New World among indigenous peoples.
Some theorists have offered other hypotheses. For example, Peter Frost puts the focus on sexual selection.
All things equal I tend to favor more ecological resolutions to questions of phenotypic evolution than sexual selective ones because the evolutionary dynamics of the latter seem to be so chaotic and difficult to characterize. Judith Rich Harris has a different spin insofar as she believes that mothers selected lighter skinned infants because they found them beautiful.
- The Relationship between Ultraviolet Radiation Exposure and Vitamin D Status
- Sunlight and Vitamin D
I am generally skeptical of this explanation simply because beauty does not emerge from a vacuum. Of course these factors are not eliminated by the selective forces sketched out above, and it seems likely that evolutionary forces are multivalent Frost in particular focuses upon hair color as opposed to skin color for his frequency dependent sexual selection model. Overall, this a good time to be interested in questions about normal human phenotypic variation.
The tools are manifold and triangulating to the most plausible explanation is far easier than in the past simply because various methods are on hand. Could be why darkish skin endured.
If light skin did begin to emerge 10, years ago in Europe then the end of the ice age might have been a factor — decreasing snow reflection decreased the need for darkish skin. Caledonian Like vitamins C and A, I always assumed that far-northern people got their vitamin D from the fresh meat and fish they ate. Jennifer Connelly and Sherilyn Fenn are halfies or quarteries, iirc. As you know, european populations have moved about to a fair extent, which should have implications for the original skin colors.
Sami have been tracked genetically to Iberian and Berber populations, while Fins language group seems to be of central european origin. So if some groups of them have managed to keep their original color variations, it may not be surprising that some of their individuals are fairly dark. Sami genetic history has been of great interest because of their large genetic distance to other European populations including their closest neighbours.
It is mainly the north Sami and east Sami that have been investigated. There is considerable genetic variation between the different Sami groups but they all share a common ancestry. Female mtDNA especially has been investigated, but also Y chromosomes and classical autosomal markers.
The research indicates that A genetic link has been established between the Sami and the Berbers of North Africa going back years Achilli Sami Y chromosomes indicate that The autosomal classic markers shows that the Sami have no close relatives in any population including their closest linguistic relatives but are in general more closely related to Europeans than people of other continents.
Tambets et al only state that South Americans, my impression is that quite a lot of the indigenous ones lived in rain forests, which would seem to help limit their exposure to the sun as compared to their co-latitudinal friends in Africa.
As a rule, with few exceptions, a good looking woman has dark eyes, dark hair, and enough coloring in her complexion to qualify as having a complexion.