Get Out and Look at Your Shadow – Vitamin D, Health and Skincare

I used to think that I would be the last person who suffer from vitamin D deficiency, since I eat tons of nuts and dark green vegetables.

I was wrong.

In 2009, a prolonged feeling of sleepiness and fatigue prompted me to have my vitamin D level tested, and the results indicated that I had a low level of 25-hydroxyvitamin D, 22 ng/ml.  My diligent use of sunscreen and sun protective clothing might have contributed to my low level of vitamin D .   It turns out that I am not alone.  Surveys conducted by the National Center for Health Statistics indicate nearly 3 out of 4 Americans have vitamin D insufficiency, and the number is higher in darker skinned races such as Hispanics (90%) and African Americans (97%).


What is Vitamin D Deficiency and Insufficiency? 

Vitamin D from sun exposure or from food is metabolized in the liver and converted into 25-hydroxyvitamin D (25[OH]D). It is the level of 25[OH]D  that is tested in a blood test..  The 25[OH]D is further metabolized in the kidneys into its active form utilized by thebody.  25[OH]D level is not only a predictor of bone health but it is also an independent predictor of risk for cancer and other chronic diseases.

The following is the terminology for different ranges of Vitamin D in the body:

Vitamin D deficiency:  25[OH]D is less than 20 ng/ml (nanogram per milliliter)

Vitmin D insurfiency: 25[OH]D is between 21-29 ng/ml

Sufficient vitamin D: 25[OH]D ≥ 30 ng/ml or even ≥ 40ng/ml

Too much vitamin D (toxic): 25[OH]D > 150ng/ml

Sources of Vitamin D

We get our vitamin D from exposure to sunlight, from our diet or from dietary supplements.  Solar UVB light (290-315nm) penetrates our skin and make vitamin D3.  Excess vitamin D3 is destroyed by sunlight, so there is no need to worry about vitamin D poisoning from over exposure to the sun (Of course over exposure to the sun has other drawbacks).  On a sunny day in Arizona, one can obtain 3000IU of vitamin D3 from the sun in 5 to 10 minutes of exposure.  However, the amount of vitamin D we get from the sun depends on where we live, the time of the day, the time of the year, and our skin color.  It may not be possible to get enough vitamin D from the sun exposure during the winter, no matter how long one stays in the sun, if the latitude is too high.  This is called vitamin D winter.  A simple test is to look at your shadow: if your shadow is longer than your height, you are not getting enough vitamin D from the sun!  You should then take vitamin D3 supplement. This rule-of-thumb applies to evaluating exposure in different seasons of the year, and also different times of day. Long shadows in the morning or late afternoon, even in the middle of summer, indicate that one is not getting much Vitamin D.

Few natural foods contain vitamin D.  Fatty fish such as herring, salmon, tuna, and mackerel are among the best sources.  Egg yolks, cheese, and beef liver also contain small amounts of vitamin D.  Vitamin D fortified foods such as milk, orange juice and some breakfast cereals are good source of vitamin D in the American diet.


Vitamin D and Health

Historically, Vitamin D deficiency was associated with rickets in children and osteomalacia (softening of the bone) in adults, and these were greatly reduced by the fortification of foods with vitamin D.  More recent studies show that rickets is only the tip of the vitamin D-deficiency iceberg, followed by osteoporosis, muscle weakness, common cancers, autoimmune diseases, infectious diseases, and cardiovascular diseases.

Most tissues and cells in our bodies have a vitamin D receptor, and some have the enzyme to convert vitamin D3 to its active form.  Adequate levels of vitamin D allow good absorption of calcium and phosphorus by our body and this in turn increases our bone-mineral-density and reduces the risk of fractures.  Vitamin D also increases our muscle strength: performance speed and muscle strength are both improved as the 25[OH]D level is increased to more than 40ng/ml.

Occurrence of cancers of the brain, prostate, breast, colon, and others can be reduced by maintaining a healthy level of vitamin D.  Once a cell becomes malignant, vitamin D also reduces the potential for the malignant cell to survive, thus decreasing the risk of cancer development.  The risk of type 1 diabetes, multiple sclerosis, hypertension, and cardiovascular disease are also reduced by taking 800-2000IU of vitamin D3 supplement.  Vitamin D deficiency is also linked with depression and increased incidence of schizophrenia.

Sunscreen and Vitamin D Supplement

In “Photoaging and Sun Protection”, we emphasize the importance of avoiding sun damage to our skin in order to slow aging and minimize the risk of skin cancer.  Studies have shown that a SPF 15 sunscreen can reduce vitamin D3 synthesis by 99%, and this sure is a contributing factor to vitamin D deficiency.  To protect our skin from the sun while getting enough vitamin D for our body, we can choose to have limited selective exposure of our arms and legs to the sun, plus a healthy dosage of 1000 to 2000IU of vitamin D3 supplement.  The supplement becomes increasingly important for those of us living at higher latitudes, since we cannot get enough vitamin D from the sun during the winter months.

How Much is Too Much?

Doses of more than 50,000IU per day are considered toxic.  Doses of 10,000IU of vitamin D3 per day for up to 5 months do not cause toxicity.  For most people, a dosage of 1000 to 4000IU of vitamin D3 is enough to maintain sufficient vitamin D level in the body.  Vitamin D2 is only 30% as effective as vitamin D3, so one needs to take about 3 times as much vitamin D2 to maintain the same level.
If you are still not convinced the necessity of maintaining a sufficient level of vitamin D, consider the report that the risk of cancer, in postmenopausal women, is reduced by 60-77% by taking 1100 IU of vitamin D3.  So, do what you can to maintain your 25[OH]D above 30ng/ml and live a long and healthy life.

Further Reading:
1. M.  Holick, “Vitamin D Deficiency”, 266-281, New England Journal of Medicine, July 19, 2007
2. A. Ginde, etc. “Demographic Differences and Trends of Vitamin D Insufficiency in the US Population, 1988-2004”, 626-632, Archives of Internal Medicine, March 23, 2009
3. J. Lappe, etc. “Vitamin D and Calcium Supplementation Reduces Cancer Risk: Results of a Randomized Trial.” 1586-91, The American Journal of Clinical Nutrition, June, 2007
4. website: