Science that’s only skin deep

Written by: Captain Skellett // December 3rd, 2010 // How Things Work, Recent Research, Science Communication, Sex and Reproduction

I’m a guest blogger for the RiAus, and this post also appeared on their fancy website. To tell the truth, I really wanted to call this post “Hormonally Yours” in homage to the Shakespeare Sisters (anyone?) but I’ll save it for another post.

Recently I was in Arnhem Land, visiting some Indigenous communities with a couple of friends. While I was there, I got pretty jealous of everybody’s darker skin. “It’s so well suited for Australia,” one of my friends lamented. “I should be in Norway or something.”

Pale skin like mine is not great for Australia. I tan pretty easily, but only after being burned bright red. While I was in the NT I slathered sunscreen religiously, but still managed to get a highly embarrassing burn on my lower back when I was building a sandcastle (an epic sand turtle, actually. Totally worth it.)

Anyway, enough about me and my weirdly tanned lower back (it’s been months! Why won’t it go away?) Let’s talk about Nina Jablonski, an anthropologist. In 2000 she suggested a new reason why skin colour varies so much. It’s not an adaptation to protect against skin cancer and sunburn, like I always thought it was.

It’s real job is to keep us highly fertile by maintaining a delicate balance between two key vitamins: Vitamin D and Folic acid.

Pica's skin tone matched her UVB exposure like her scarf matched her dress. Image by Monja Con Patines

Vitamin D is obtained through some foods, but mostly from drinking in sunshine. UV light turns cholesterol into Vitamin D, which then goes to either your liver or kidneys to be converted to an active form.

Once active it helps white blood cells like macrophages kill bacteria, and helps control levels of calcium and phosphate – important for building healthy bones.

Deficiency in Vitamin D causes rickets, a disease resulting in soft, easily broken bones and deformity which can lead to early death.

So getting enough UV (specifically UVB light) is important to not dying, and therefore having reproductive success later in life. It’s been backed up by Yuen, A. (Vitamin D: In the evolution of human skin colour DOI: 10.1016/j.mehy.2009.08.007)

Natural selection favours soaking up UV.

Penny stayed under foliage at noon to protect her folic acid. Image by Monja Con Patines

Folic acid is obtained in leafy vegetables and fortified cereals. Rather than being made by UV, the light can destroy folic acid by literally breaking it apart. (Jablonski, N. The evolution of human skin coloration DOI: 10.1006/jhev.2000.0403)

Critical for DNA synthesis, folic acid is essential during pregnancy when a lot of new cells are being made.

Folic acid prevents against 70% of neural tube defects in embryos. Its destruction by UV is bad news.

Natural selection favours avoiding UV.

So there’s an ideal amount of UV light that needs to get through the skin – enough to produce Vitamin D, but not too much to destroy all the folic acid. Getting the balance right for the environment you’re in means higher fertility, which drives natural selection

This is what Nina Jablonski thinks caused the evolution of skin colour through the sepia spectrum we see today. Dark skin, with high melanin, stops more UV light. That’s exactly what you want if you live in a place with a lot of sun, like places near the equator. Light skin lets more UV in, which is great if you live somewhere overcast and not very high on UV.

Understanding how your skin colour (NOT your race) influences these two vitamins is important in being healthy. It’s more important now than ever, because we humans travel a LOT.

Sadly, Australia is pretty high in UV and I am pretty white. Thank god for sunscreen.

Things are rarely that simple though, and I imagine there’s a few different things going on that connect UV light to skin colour.

On Tuesday the RiAus is holding an event called Skin Deep: Exploring human ancestry. They’ll be showing a preview of a new SBS documentary about skin colour scientific research, as well as results from the Genographic Project. Basically they took DNA samples from a lot of volunteers and some national identities, and now they’re giving us the goss on who’s related to who’s secret love child.

I’ll be there, I’d love to see you (though seats are limited.) I’ll be the one tweeting in the corner. Follow me @CaptainSkellett

Would love to hear from anyone who took part in the Genographic Project, and anyone who didn’t. Who would you most like to be related to? For me it’s David Attenborough, then I can dream of inheriting his voice.

Captain Skellett

I be Captain Skellett. Me blog started in April 2009 when I was working full time and didn’t get a chance to talk science. Now I have changed jobs and talk science all the time, but that doesn’t stop me blogging. More About Captain Skellett   Google

   

2 Responses to “Science that’s only skin deep”

  1. Lere says:

    PROFESSOR Frank Garland, and his brother, Cedric, recommend [...] taking 50,000 units of vitamin D per week for eight to twelve weeks followed by maintenance on 1,000 to 2,000 units a day”.
    ACCORDING Cedric F. Garland, Dr. P.H., FACE, Department of Family and Preventive Medicine and Moores Cancer Center of the University of California, San Diego (UCSD), “It is projected that raising the minimum year-around serum 25(OH)D level to 40-60 ng/ml (100-150 nmol/L) would prevent approximately 58,000 new cases of breast cancer and 49,000 new cases of colorectal cancer each year, and three quarters of deaths from these diseases, in the US and Canada.”
    Plasma vitamin D and mortality in older men: a community-based prospective cohort study.
    “There was a U-shaped association between vitamin D concentrations and total mortality. An approximately 50% higher total mortality rate was observed among men in the lowest 10% (98 nmol/L [or 39 ng/ml]) of plasma 25(OH)D concentrations compared with intermediate concentrations. Both high and low concentrations of plasma 25(OH)D are associated with elevated risks of overall and cancer mortality.
    Dr. Frank C. Garland, 1950-2010
    “Tuesday, August 17 at UCSD Thornton Hospital after contending with a nearly year-long illness.“

    “African Americans … are more likely to be vitamin D deficient due to their darker skin pigmentation’s ability to block the sun’s rays”
    It is not true that melanin blocks the wavelengths which synthesize vitamin D . The value of melanin as a sunscreen (2010).
    “epidermal melanin is not a neutral density filter providing no or minimal protection for the induction of erythema at 295 and 315 nm and some protection at 305 and 365 nm”
    It does block 305nm but around that wavelength is the most damaging A UVB Wavelength Dependency for Local Suppression of Recall Immunity in Humans Demonstrates a Peak at 300 nm. also see Erythema curve. Note the relative danger curve ( yellow) peaks at around 305nm
    T the blocking of a limited spectra of vitamin D synthesizing UVB doesn’t matter the other wavelengths get through. Blood vitamin D levels in relation to genetic estimation of African ancestry “found novel evidence that the level of African ancestry [rather than skin pigmentation] may play a role in clinical vitamin D status”.
    There is a negative feedback system; evolution has has got vitamin D levels just right
    Klotho protein deficiency and aging.
    “α-Klotho protein is shown to function in the negative feedback regulation of vitamin D3 synthesis These observations indicated that abnormal vitamin D3 metabolism is the main cause of aging phenotypes.″
    Klotho was named after one of the Moirae or fates, supplementing vitamin D is indeed a fateful step.

    Many people of tropical ancestry have a optimum homeostasis of vitamin D which is below the new IoM levels, but if they’re wise they’ll not take supplements

    [Reply]

    Wow, that is an epic comment!

    [Reply]

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