What Causes Vitamin D Deficiency?

When sunlight shines on our skin, it makes vitamin D. Through the long history of man’s evolution, our bodies learned to rely on this plentiful supply of vitamin D.

Until a few thousand years ago (in evolutionary terms, just an eye-blink) we spent much of our time in the sun, hunting, gathering and having fun. Vitamin D deficiency probably didn’t exist.

Our bodies also learned to store vitamin D, for a rainy day.

So even fair-skinned races living in temperate zones would have obtained all the vitamin D they needed, storing the excess on sunny days, and using it up when the sun didn’t shine for a while.

At the end of summer, their vitamin D levels would have been optimum, then would have gradually declined to moderate levels during winter.

That was then. So what’s gone wrong?

What Causes Low Vitamin D?

Basically, we don’t get enough sunlight on our skin, so we can’t make enough vitamin D3.

Why don’t we get enough sunlight?

Many of us live far from the tropics, so strong sunlight is not available to us for much of the year
We work indoors
We clothe our bodies
In cities, high-rise buildings create perpetual shade (no UV-B)
City haze and other man-made air pollution absorbs most of the UV-B in the sunlight. Without UV-B we can’t make vitamin D.
When we travel to work or relax at home, we often stay behind glass, which UV-B cannot penetrate.
Finally when we venture outdoors, we cover up with sunscreen to protect our skin from sun-damage, aging and cancer.

Is it any wonder that we are vitamin D deficient?

We have similar bodies to our ancestors. But they did most of their hunting and gathering in the sun. We mostly don’t. As a result, many of us are chronically deficient in vitamin D.

Those with dark complexions who live in temperate or polar zones are worst affected.

But, with our current lifestyles, even fair-skinned people these days can suffer from severe vitamin D deficiency.

Who is most at risk of vitamin D deficiency?

Most likely to be deficient in vitamin D are:

Older people – as we get older our skin makes substantially less vitamin D
Blacks and dark-complexioned people, especially those who live in temperate zones
People who live where sunshine is scarce or ultraviolet (UV-B) light levels are low
People who don’t get much sunlight on their skin, for whatever reasons
People who usually wear sunblock
People who sit behind glass (window glass absorbs the UV-B rays that create vitamin D3 in the skin)
Exclusively breastfed infants whose mothers are vitamin D deficient. (Other infant food is often fortified with vitamin D.)
People who have difficulty absorbing dietary fat. (Vitamin D is fat-soluble.) This may include sufferers from Crohn’s disease, cystic fibrosis or liver disease.
Obese or heavily overweight people have difficulty building up their vitamin D stores, for reasons which are not yet fully understood.

Many of us are constantly deficient in vitamin D. In recent US surveys of vitamin D blood levels