Vitamin D Deficiency

  • Author:
    Betty Kovacs, MS, RD

    Betty is a Registered Dietitian who earned her B.S. degree in Food and Nutrition from Marymount College of Fordham University and her M.S. degree in Clinical Nutrition from New York University. She is the Co-Director and Director of nutrition for the New York Obesity Research Center Weight Loss Program.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Quick GuideNutritional Health Pictures Slideshow: Amazing Vitamin D, Nutrition's Newest Star

Nutritional Health Pictures Slideshow: Amazing Vitamin D, Nutrition's Newest Star

What causes a vitamin D deficiency?

There are many possible causes of vitamin D deficiency.

Limited exposure to the sun

You may look out your window and see the sun shining and think that you are safe from this deficiency, but that is not always the case. Even in sunny climates there is an increased prevalence of vitamin D deficiency. We have all heard about the dangers of skin cancer and the need for sunscreen to protect us from this disease. This knowledge and the preventive actions we take have significantly decreased our vitamin D levels. Sunscreen protects so well against UV-B rays that an SPF of 30 decreases vitamin D synthesis in the skin by more than 95%. On top of this, we tend to spend more time indoors. One study found that it took Caucasians exposure of more than 30% of their body every day in the summer to make the optimal amounts of vitamin D. Most adults work indoors and wear more clothing during the work week, which leaves only about 10%-15% of their body exposed to UV for short periods, so they cannot meet their vitamin D needs through the sun alone. Even if you do have some exposure to the sun, the total amount of vitamin D you can produce is affected by the season, time of day, ozone amount, latitude, and number of clouds in the sky.

The important thing about using the sun for vitamin D production is to know that less is more. You are better off with short regular exposures to the sun rather than prolonged exposure for many reasons. The process is not as simple as the sun hitting your skin and vitamin D appearing in your blood. What actually happens is that vitamin D3 is first transformed by a process known as hydroxylation in the liver to 25-hydroxyvitamin D3, often written as (25(OH)D3), and then again in the kidney to its active form, 1,25-dihydroxyvitamin D3, written as (1,25(OH)2D3). The level that is checked in your blood is 25-hydroxyvitamin D, often written as 25(OH)D, which includes vitamin D2 and D3. By staying in the sun, you limit this process and can actually get less vitamin D. You also have a lower risk of burning and damaging your skin with short exposures.

The National Cancer Council in Australia recently published a position paper on ways to minimize the risk of skin cancer while maintaining adequate vitamin D levels via exposure from the sun. Currently, one-third of the population there is deficient. Extended and deliberate sun exposure without any form of protection when the UV index is 3 or above is not recommended for anyone. When the UV index is below 3, sun protection is not recommended, and it is recommended that people be outdoors in the middle of the day with some skin uncovered on most days of the week.

Darker skin

Melanin is what gives skin its color. Lighter skin has less melanin than darker skin. Melanin is able to absorb UV-B radiation from the sun and reduce the skin's capacity to produce vitamin D3 by 95%-99%. People with a naturally dark skin tone have natural sun protection and require at least three to five times longer exposures to make the same amount of vitamin D as a person with a white skin tone. African Americans have a population mean serum 25(OH)D level of 16 ng/mL, whereas white Americans have a level of 26 ng/mL. Continue Reading

Reviewed on 6/9/2016
References
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