Vitamin D-3, a fat-soluble vitamin, is obtained through diet and your skin also makes vitamin D when it's exposed to sunlight. Fortified foods, such as milk, cereals and juices, supply most of the vitamin D in the diet. Vitamin D aids calcium absorption, prevents rickets, growing bones require it and, together with calcium, it protect adults from osteoporosis. Dietary supplements can cause toxicity, so consult a doctor before taking vitamin D supplements.
Recommended Dietary Allowance
The Recommended Dietary Allowance, or RDA, is the average daily level of intake sufficient to meet the nutrient requirements of 97 to 98 percent of healthy people. The Institute of Medicine established an RDA for vitamin D, set on the basis of minimal sun exposure. For people aged one to 70, the RDA is 600 IU, and 800 IU for those over 70. As an example of how the RDA can be met through diet, three recommended 8-oz. servings of low-fat milk provides 300 IU; 3 oz. of sockeye salmon contributes 447 more IU; and one additional 8-oz. serving of fortified juice provides 100 IU; together this totals 847 IU.
Maximum Daily Levels of Intake
The Institute of Medicine set a maximum daily intake for vitamin D at a level unlikely to cause adverse health effects, called the tolerable upper intake level, or UL. This value is 4,000 IU for adults and children aged 9 years and older. Long-term intakes above the UL increases the risk of serious adverse events, such as greater risk of certain cancers and cardiovascular events, more falls and fractures among the elderly and increases in all-cause mortality. If you buy vitamin D supplements, use caution and read product labels, as dosages can vary from 400 IU to 10,000 IU.
Percent Daily Values of Vitamin D
The U.S. Food and Drug Administration developed Daily Values, or DVs, to help consumers compare food product nutrients based on a daily 2,000-calorie diet. The DV recommended dosage for vitamin D is 400 IU for people aged 4 and older. Foods with vitamin D added must list the vitamin D content on the label, commonly shown as a percent DV per serving. Milk provides approximately 25 percent of the DV in an 8-oz. cup, while 1 tbsp. of fortified margarine may contain 15 percent. Juice products may provide 25 percent of the DV per 8-oz. serving, but products vary in amounts added, as do fortified yogurts.
Warnings and Considerations
Toxicity can occur from high intakes of dietary supplements. Excessive vitamin D intake can cause vomiting and weakness and can raise blood calcium levels, causing confusion and abnormal heart rhythms. Excessive vitamin D intake over time can cause depression, headaches, sleepiness and bone loss. It can also cause arteries and other soft tissues of the body, such as the heart, lungs and kidneys, to become hardened and lined with layers of calcium. Calcium supplements and certain medications should not be taken with vitamin D as serious drug interactions may occur.
References
- Linus Pauling Institute; Vitamin D; Jane Higdon; December 2010
- MedlinePlus; Vitamin D; November 2010
- Office of Dietary Supplements; Vitamin D; February 2011
- American Cancer Society; Vitamin D; December 2010
- U.S. Food and Drug Administration; Appendix F: Calculate the Percent Daily Value for the Appropriate Nutrients; March 2011
- Drugs.com; Cholecalciferol; December 2010
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