The exposure of the skin to solar ultraviolet B (UVB; 290–315 nm) radiation is considered as the most important sources of vitamin D. Vitamin D is rare in food. Among the vitamin D-rich food, oily fish are considered to be one of the best sources. The other factors that affect the cutaneous vitamin D synthesis are seasons, time of day, the length of the day, cloud cover, smog, skin melanin content, and sunscreen (1). UVB radiation does not penetrate glass, so exposure to sunlight indoors through a window does not produce vitamin D.
Complete cloud cover reduces UV energy by 50%; shade (including that produced by severe pollution) reduces it by 60%. Individuals with restricted sun exposure need to include good sources of vitamin D in their diet or take a supplement to achieve recommended levels of intake (2). National Health and Nutrition Examination Survey showed that the intake of vitamin D from food sources and dietary supplements was not meeting recommended levels. Dairy products were the primary sources of both vitamin D and Calcium. Additional food fortifications, as well as dietary and supplement guidance, are needed for the general population (3).
Vitamin D Food source Table
| Selected Food Sources of Vitamin D (4) | ||
| Food | IUs (International Units) per serving | Percent DV (Daily Value)* |
| Cod liver oil, 1 tablespoon | 1,360 | 340 |
| Swordfish, cooked, 3 ounces | 566 | 142 |
| Salmon (sockeye), cooked, 3 ounces | 447 | 112 |
| Tuna fish, canned in water, drained, 3 ounces | 154 | 39 |
| Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D, varies) | 137 | 34 |
| Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup | 115-124 | 29-31 |
| Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV) | 80 | 20 |
| Margarine, fortified, 1 tablespoon | 60 | 15 |
| Sardines, canned in oil, drained, 2 sardines | 46 | 12 |
| Liver, beef, cooked, 3 ounces | 42 | 11 |
| Egg, 1 large (vitamin D is found in yolk) | 41 | 10 |
| Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the DV) | 40 | 10 |
| Cheese, Swiss, 1 ounce | 6 | 2 |
*The DV for vitamin D is currently set at 400 IU for adults and children age 4 and older. Food labels, however, are not required to list vitamin D content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
References
1. Chen, Tai C., et al. “Factors that influence the cutaneous synthesis and dietary sources of vitamin D.” Archives of biochemistry and biophysics 460.2 (2007): 213-217.
2. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h3
3. Moore, Carolyn, et al. “Vitamin D intake in the United States.” Journal of the American Dietetic Association 104.6 (2004): 980-983
4. U.S. Department of Agriculture, Agricultural Research Service. 2011. USDA National Nutrient Database for Standard Reference, Release 24. Nutrient Data Laboratory
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