1. Amazing Vitamin D Slideshow Pictures
2. Take the Vitamins Quiz

Author:

Betty Kovacs, MS, RD

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.

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Medical Editor:

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.

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In this Article

• What is vitamin D?
• What does vitamin D do for one's health? What are symptoms and signs of vitamin D deficiency?
• What causes a vitamin D deficiency?
• How is a vitamin D deficiency diagnosed?
• What is the treatment for a vitamin D deficiency?
• Can vitamin D deficiency be prevented?
• What are symptoms and signs of an excessive vitamin D intake?
• Vitamin D FAQs
• Patient Comments: Vitamin D Deficiency - Tests
• Patient Comments: Vitamin D Deficiency - Treatment
• Patient Comments: Vitamin D Deficiency - Symptoms
• Find a local Doctor in your town
• Vitamin D Deficiency Index

Do you know your vitamin D level? Do you think that you could be deficient in vitamin D? With plenty of sunshine available, it may surprise you to know that an estimated 1 billion people are deficient or insufficient in vitamin D. This is estimated because undiagnosed vitamin D deficiency is common worldwide.

The major source of vitamin D is natural sun, so limiting our exposure to it has the biggest impact on vitamin D deficiency. We have all heard about the dangers of skin cancer and the need for sunscreen to protect us from this disease. Unfortunately, no one discusses the dangers of not getting vitamin D from the sun and ways to compensate for it. Using a sunscreen with SPF of 30 decreases vitamin D synthesis in the skin by more than 95%. 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. Getting 10 to 15 minutes of sun exposure a couple of times per week can be enough for many people.

Melanin is what gives skin its color. Lighter skin has less melanin than darker skin. Melanin is able to absorb UVB radiation from the sun and reduce the skin's capacity to produce vitamin D3. 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.

Research has begun to show a relationship between BMI and vitamin D deficiency. A study done on 2,187 overweight and obese subjects found that those with a BMI above 40 had 18% lower serum vitamin D levels than those with a BMI under 40. Another study done compared the vitamin D levels of 154 obese subjects to those of 148 nonobese subjects and found that the obese subjects' vitamin D levels were 23% lower. Some possible reasons for this are lower intakes of vitamin D, less exposure to sunlight (UV radiation), and a higher distribution volume of vitamin D. Even with exposure to sunlight, there remains a risk for a deficiency. One study tested the blood levels of vitamin D after sun exposure in both obese and nonobese subjects. It found that there was 57% less vitamin D in the blood of the obese subjects. The exact cause is not known. This emphasizes the importance of having your levels checked regardless of your sun exposure or dietary intake.

People with one of the fat malabsorption syndromes (for example, Crohn's disease, celiac disease) and people who have had bariatric surgery are often unable to absorb enough of the fat-soluble vitamin D.

It has been shown that as we age our body has a decreased ability to synthesize vitamin D from exposure to the sun.

A wide variety of medications, including antifungal medications, anticonvulsants, glucocorticoids, and medications to treat AIDS/HIV can enhance the breakdown of vitamin D and lead to low levels. There is also a loss of vitamin D for those with chronic kidney disease, primary hyperparathyroidism, chronic granuloma-forming disorders, and some lymphomas.