Vitamin D: The Story Behind Our Skin Color

a woman at the beach pointing her face up at the sun

These are summer days in Michigan, and everyone is out and about, enjoying the sunshine. Michigan is a double peninsula, “upper” and “lower,” surrounded by water. As a result, our skies are often overcast, even in summer. And given our northern latitude, winters are long and sunny days are few. The result is that much of the year, we get little to no sun exposure.

Unfortunately, this is associated with chronic vitamin D deficiency in much of Michigan’s population. In this month’s column, I’d like to share information about vitamin D and its role in our health.

Vitamin D is a hormone produced by the skin in response to exposure to UV light. It circulates in the blood stream, and when it enters cells, it binds to and activates vitamin D receptor, which is a transcription factor that binds to DNA and regulates gene expression. Vitamin D is widely recognized to be important for bone health and calcium metabolism. A less well-known role is that it is a master regulator of the immune system. It is also involved in metabolism, brain health, cancer surveillance, and many other biological roles – all critical for a healthy body.

Vitamin D is so important that over the course of human evolution, it gave rise to the skin color difference among people from different parts of the world. Yes! The skin color difference that gets all that media attention these days – “black,” “white,” and “brown,” – is actually an evolutionary solution to the problem of vitamin D. Homo sapiens originated in central West Africa, along the equator, where sunshine is strong and plentiful. Melanocytes producing plentiful melanin pigment produced dark skin that provided protection from the sun’s damaging UV rays. The sun is so strong along the equatorial regions of Africa that even with dark skin, production of vitamin D was robust.

But as H. sapiens migrated – first to the Horn of Africa, then across the straits to what is now Yemen, then north and east to what is now the Indian subcontinent, and from the subcontinent out to the rest of the world – humans encountered less and less sunlight. In Europe, once you pass the 45th parallel, and certainly the 60th parallel (Scandinavia), the sunlight is so weak that vitamin D production plummets. Evolutionary pressure led to an effective solution – mutations in pigment production that make the skin lighter to reduce UV light absorption. The further north that H. sapiens migrated, the more robust the mutations and the lighter the skin. This works well for humans who live in far northern climates – the sun is weak, so there’s less risk of cancer and hence lighter skin is tolerated and vitamin D production is preserved.

Fast forward to the last few hundred years, in which mass human migration moved dark skinned people north to low-sunlight regions and light skinned people south to high-sunlight regions. The result is that light skinned people get skin cancer (e.g. basal cell carcinoma, squamous cell carcinoma and melanoma), and dark skinned people get vitamin D deficiency.

Which brings us back to our topic. It turns out that African Americans have among the highest rates of inflammatory conditions of any population in the world. That’s not true for Africans, or for people of African descent who live in Brazil, etc.

Why is that? Because vitamin D is a master regulator of the immune system, and vitamin D deficiency is a risk factor for auto-immune conditions such as multiple sclerosis, Graves disease, sarcoidosis, lupus and rheumatoid arthritis, among many others.

If you are dark skinned and living in Michigan (long winters, overcast, northern latitude), and furthermore you work in an office 8 am to 5 pm (primary sunlight time), you just can’t get enough sun to produce a sufficient amount of vitamin D.

In my clinical work as an oculofacial plastic and orbital surgeon, I take care of patients with inflammatory diseases of the orbit – the tissues around the eye. Every autoimmune disease can have manifestations in the tissues around the eye, and management can be quite complex because these diseases (such as thyroid eye disease) can damage vision as well as deform the face.

Research in my laboratory revealed that vitamin D deficiency is an important risk factor for development of thyroid eye disease, so I check vitamin D levels regularly. Indeed, patients who present with severe inflammation are much more likely to have vitamin D deficiency.

So how do we treat it? And how do we prevent vitamin D deficiency? The answer is oral supplementation. I am personally prone to vitamin D deficiency – I have Mediterranean skin, tan easily, work indoors, and live in Michigan. So I have my serum vitamin D levels checked once a year, and I take supplements. Vitamin D3 is the form available over the counter, while vitamin D2 is the prescription version. For all practical purposes, they are both equally effective. Most Michigander adults would benefit from around 3000 international units (IU) per day, and the goal is to get the serum 25-hydroxy-vitamin D to between 50-100 ng/mL. Children would also benefit, but dosing should be done by a pediatrician.

And if you are lighter skinned, please don’t go lay in the sun for vitamin D – you’ll get skin damage, age prematurely, and be prone to skin cancer. Use sunscreen and take a vitamin D supplement. In my work, I also take care of skin cancer around the eye. In fact, my team just published a major clinical trial on the treatment of basal cell carcinoma affecting the eyelids and orbit, so it’s a major part of my practice. I can rebuild eyelids damaged by cancer, but I prefer that you will not need my services.

So get to your PCP, request a vitamin D blood test, and go from there. Contact us when you’re ready.

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