Over 40 percent of all adults in the United States lacked adequate vitamin D in 2006, according to the National Health and Nutrition Examination Survey. In 2010, the Institute of Medicine increased its recommended dietary allowances for vitamin D from 400 to 600 international units per day for most adults and 800 international units per day for people over 70. The best way to increase the level of vitamin D in your body is through exposure to the sun, but you can also get vitamin D from certain foods or supplements.
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Soaking Up the Sunlight
Vitamin D exists in two forms: ergocalciferol, or D-2, and cholecalciferol, or D-3. Your skin produces vitamin D-3 when exposed to ultraviolet B radiation from the sun. Exposure of your arms, legs or back for five to 30 minutes between 10 a.m. and 3 p.m. twice a week is recommended to achieve adequate levels. Darker skin, advanced age and sunscreen use reduce your skin’s ability to synthesize vitamin D. Additionally, latitude, season and time of day greatly affect the amount of vitamin D your skin can produce from exposure to the sun. In most of the United States, very little vitamin D is synthesized in the skin during the winter months.
Foods Naturally High in Vitamin D
Vitamin D, in the form of both D-2 and D-3, is found naturally in some foods. The best natural food sources of vitamin D are oily fish, including mackerel, halibut, salmon, tuna and rainbow trout. Cod liver oil is an excellent source, providing 1,360 international units of vitamin D in 1 tablespoon. Mushrooms, including maitake and portobella, are a good sources of vitamin D, especially when they have been exposed to ultraviolet light. Egg yolks and cheese also provide small amounts of the vitamin.
Foods Fortified with Vitamin D
When a food is fortified, vitamins or minerals that weren’t originally in the food are added to it to make it more nutritious. Because so few foods naturally contain vitamin D, many are fortified to help consumers get more of this essential vitamin. Foods often fortified with vitamin D include milk, yogurt, orange juice, cereals, bread and soy products, including tofu and soy milk. Check nutrition labels to determine whether the foods you eat are fortified and how much vitamin D they provide.
Vitamin D is available as a dietary supplement in the form of vitamins D-2 and D-3. While these two forms are generally regarded as equivalent, evidence suggests that at high doses vitamin D-2 may be less potent than D-3. If you are vitamin D-deficient, your health care provider may recommend exceeding the recommended dietary allowance until your blood levels return to normal. Do not exceed the upper level intake of 4,000 international units per day for individuals over 9 years of age unless directed to do so by your doctor.
REFERENCES & RESOURCES
- National Academy of Sciences: Institute of Medicine: Dietary Reference Intakes for Calcium and Vitamin D: Report Brief
- New England Journal of Medicine: Vitamin D Deficiency
- Journal of Clinical Endocrinology and Metabolism: Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline
- USDA: National Nutrient Database for Standard Reference
- National Institutes of Health: Vitamin D: Fact Sheet for Health Professionals
- Nutrition Research: Prevalence and Correlates of Vitamin D Deficiency in US Adults
- National Academy of Sciences: Institute of Medicine: DRIs for Calcium and Vitamin D
- National Institutes of Health: Vitamin D Fact Sheet for Consumers
- USDA National Nutrient Database for Standard Reference: Vitamin D Content of Selected Foods