Sunlight and vitamin D — myth or fact

Sunlight and vitamin D — myth or fact

Vitamin D is categorized as a vitamin; yet in many ways it acts more like a hormone.

Vitamin D is categorized as a vitamin; yet in many ways it acts more like a hormone.

by Dr. Alan Christianson — 

In medical school, I was taught that vitamin D was more of a liability than a necessity. It was believed that no one was deficient in it, aside from children living through Alaskan winters. It was also believed that amounts greater than a few hundred units per day could be toxic to the liver. The last few decades, however, have witnessed significant changes to what we know about vitamin D.

Vitamin D is categorized as a vitamin; yet in many ways it acts more like a hormone. In the past, the bulk of vitamin D we had in our bodies came from our skin. Our skin made vitamin D when stimulated to do so by sunlight. Our bones need small amounts of vitamin D to form properly — specifically, a blood level of at least 30 ng/ml.

Recently, we have learned that the immune system needs higher amounts of vitamin D to function at its best — the standard range for immune health being 45 to 70 ng/ml. It is interesting to note that several studies of hunter-gatherers living in equatorial Africa found that this is their typical range.

What happens if you are not in this range? You could experience symptoms such as fatigue, weight gain, headaches, constipation, chronic pain, muscle cramps, overall weakness and concentration difficulty.

You are at higher risk for many diseases, including 17 different types of cancer, autoimmune disease, obesity, arthritis, gout, heart disease, fibromyalgia, Alzheimer’s disease, psoriasis, multiple sclerosis and many others.

But here comes the twist. For the last 18 years, I have been practicing medicine in Scottsdale, Ariz. We average roughly 300 days of sunlight per year — although, on a hot summer day it seems like the average is more like 365 days.

When I began testing patients’ vitamin D levels, I was shocked to see that (without exaggeration) 99 percent of my patients were below the optimal levels. Most patients are surprised when I tell them they are deficient, as the common belief still exists that vitamin D is easily made by the body from exposure to the sun.

People often say they do not take the vitamin because they are frequently outside or they only take it in the wintertime when they are outside less. My experience has been that people who work outdoors as roofers or landscapers are just as low in vitamin D as office workers. A recent study confirmed this and has even suggested that the sun may work against our vitamin D levels.

A professor studied vitamin D levels in surfers and skateboarders from Hawaii. These young people primarily had light skin, which is more able to absorb vitamin D. They also averaged 11 hours outdoors daily, without sunscreen. Yet, their blood levels of vitamin D averaged only 30 ng/ml — barely enough for healthy bones and far too little for good immune function.

What could explain these low levels of vitamin D in young people who spend so much time outdoors? Some past evidence shows vitamin D requires certain oils from the skin in order to be formed. It seems these oils take time to form on the skin and are easily washed off with soapy water. Once these oils are lost, no matter how much the skin is exposed to sun, vitamin D is no longer made.

How do you go about getting the right amount of vitamin D? Well, there are only two ways to go: Stop bathing, stop wearing clothes and spend the bulk of your time outside in a sunny location; or take a vitamin D supplement and monitor your blood levels.

When you put it like that, taking the pill does not seem like such a bad idea. How much vitamin D should you take? If it turns out you are low, most people need 5,000 to 10,000 units per day to get up to a healthy range.

It is good to have your blood tested every three months until you are in the target range. Here are a few tips. First, it usually takes a higher dose to get to a good level than it takes to stay there. Some people need to reduce their dose to 2,000 to 5,000 units after they have stabilized.

However, wide variation can exist from person to person. Some may only need a few thousand units, while others may need 20,000. Second, vitamin D is fat-soluble and is much better absorbed when taken with a meal that contains healthy fats like avocados or nuts and seeds.


Haddad, J.G., Chyu, K.J. Competitive protein-binding radioassay for 25-hydroxycholecalciferol. J Clin Endocrinol Metab. 1971 Dec;33(6):992-5.

Luxwolda, M.F., Kuipers, R.S., Kema I.P., Janneke, Dijck-Brouwer, D.A., Muskiet, F.A. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr. 2012 Jan 23:1-5.

Binkley, N., et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007 Jun;92(6):2130-5.


Alan Christianson, N.M.D., has practiced at Integrative Health in Scottsdale, Ariz., for more than 15 years. He is the author of The Complete Idiot’s Guide to Thyroid Disease. 480-657-0003 or

Reprinted from AzNetNews, Volume 33, Number 6, December 2014/January 2015.

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