Vitamin D, a critical element in bone growth and maintenance, also offers protection against many different diseases.
Vitamin D Health Benefits
Vitamin D is critical for calcium absorption and plays an important role in the prevention of osteoporosis. It is also involved in immune function and inflammation reduction.
Supplementation with calcium and vitamin D reduces the risk of bone loss and fractures among older people. Vitamin D also has a protective effect against colon cancer, and possibly cancers of the breast and prostate as well. In addition, there is a growing body of evidence suggesting that vitamin D may help to prevent diabetes, autoimmune diseases such as multiple sclerosis, periodontal (gum) disease, high blood pressure, and heart disease.
A vitamin D deficiency in children can cause a bone disease called rickets, and vitamin D-deficient adults can develop osteomalacia, which results in weak bones and muscles. Muscle weakness and pain in the bones or joints may indicate inadequate vitamin D intake.
Recommended Vitamin D Intake
There is disagreement among the experts regarding vitamin D requirements. For optimum health, the National Osteoporosis Foundation (cited by the University of Maryland Medical Center, 2011) recommends:
- 400-800 IU per day for adults up to 50 years of age
- Up to 2,000 IU per day for those above 50 years of age
Natural Food Sources of Vitamin D
The best food sources of vitamin D are seafood and fish liver oils. The only vegetables that naturally contain vitamin D are mushrooms. Other foods are also commonly fortified with vitamin D, such as milk and many breakfast cereals. Total IUs (International Units) for some good sources of vitamin D are as follows:
- Herring, fresh, 3 ounces – 1,383
- Cod liver oil, 1 tablespoon – 1,360
- Salmon, Sockeye, baked or broiled, 4 ounces – 740
- Herring, pickled, 3 ounces – 578
- Salmon, pink, canned, 3 ounces – 530
- Halibut, 3 ounces – 510
- Catfish, 3 ounces – 425
- Salmon, Chinook, baked or broiled, 4 ounces – 411
- Mackerel, Atlantic, 3 ounces – 306
- Oysters, 3 ounces – 272
- Shiitake mushrooms, dried, 4 – 249
- Tuna, canned in oil, 3 ounces – 200
- Shrimp, 3 ounces – 129
- Milk (whole, reduced fat, and nonfat, fortified), 1 cup – 98
- Shiitake mushrooms, 100 grams, cooked – 96
- Cereal, fortified, 1 cup – 40 or more
- Sardines, Atlantic, canned in oil – 33 each
- Egg, 1 whole – 20-26
- White button mushrooms, 100 grams – 18
- Beef liver, cooked, 3.5 ounces – 15
- Swiss cheese, 1 ounce – 12
For those who can’t obtain sufficient vitamin D through food sources, there are two options: sunshine and supplements.
Vitamin D Through Sun Exposure
Under the right conditions, people under 50 years of age can obtain sufficient vitamin D via 5 to 30 minutes of direct sun exposure between 10 am and 3 pm, twice a week or more (experts disagree on the ideal exposure time). However, there are many factors that make it difficult to get enough vitamin D through sun exposure:
- Cloud cover, shade, and pollution-induced smog can reduce UV energy by 50-60%.
- Sunscreen blocks UV rays (though most people don’t apply enough or miss a few spots, letting the sunshine in).
- In many places, UV energy is not sufficient for the synthesis of vitamin D year-round. In Canada, sunlight doesn't provide adequate vitamin D from October to March. Only at latitudes below 34 degrees north can vitamin D be obtained via sunlight throughout the year.
To obtain vitamin D through sunshine, the sun must reach some uncovered skin – having the sun shine on one’s face and arms is sufficient. It’s not necessary to lie outside in a bikini or a pair of shorts to obtain the benefits of sunshine.
Moderate use of tanning beds can also induce vitamin D synthesis, as long as they emit 2% to 6% UVB radiation. But given the risk of skin cancer, many people prefer not to expose their skin to outdoor sun or tanning bed rays.
Unfortunately, it’s not possible to obtain vitamin D via sunlight shining through a window, as UVB radiation doesn't penetrate glass. Those who don't eat enough vitamin D-rich foods and avoid sun exposure may require supplementation.
Vitamin D Supplements
The risk of vitamin D deficiency increases after age 50 because older adults don’t synthesize it as efficiently. Health Canada recommends that adults over 50 take vitamin D supplements. Other risk factors for vitamin D deficiency may also create a need for supplementation. In addition to age, risk factors include:
- Being housebound
- Certain illnesses and medications
- Dark skin
- Northern climate
- Obesity
- Regular use of sunscreen
- Wearing full body coverings
- Working indoors all day (or working night shifts and sleeping all day)
Babies who are breast-fed by vitamin D-deficient mothers are also at risk.
Vitamin D Risks
Vitamin D can be toxic in high doses. While it’s not possible to overdose on vitamin D via sun exposure, excessive supplementation poses a serious risk, and vitamin D may also interfere with certain medications. Those who suffer from medical conditions or take medications should consult a medical practitioner before taking supplements.
This article was last updated March 4, 2012.
Further Reading
For more information on vitamins and minerals, see Vitamin E Health Benefits and Risks, Vitamin B for Anxiety and Panic Disorder, and Foods That Maximize Calcium's Health Benefits.
References:
- George Mateljan Foundation. (2009). “Vitamin D.” The World’s Healthiest Foods, WHFoods.com.
- Health Canada. (2007). “Vitamin D for People Over 50: Background.” HC-SC.gc.ca.
- Hiller, S. (3 August 2009). “Avoid Osteoporosis the Natural Way – Natural Protection for Your Bones.” The Mayo News. MayoNews.ie.
- Mushrooms Canada. (n.d.). “Vitamin D.” Mushrooms.ca.
- National Institutes of Health – Office of Dietary Supplements. (2011). “Dietary Supplement Fact Sheet: Vitamin D.” Dietary-Supplements.info.nih.gov.
- University of Maryland Medical Center. (2011). “Osteoporosis.” UMM.edu.
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