Vitamin D: Balancing Cutaneous and Systemic Considerations

South Med J. 2001;94(1) 

In This Article

Vitamin D And Diet: Often Not Enough

The name ascribed to cholecalciferol and the related metabolites is a misnomer by having the label "vitamin" attached to "D." Although it would more appropriately be considered a secosteroid hormone, vitamin D was discovered during the period (the late teens and early 20s of the 20th century) when "vital amines" were being discovered in foods.[31,32] The name implies "nutrient," but it is exceptionally difficult to obtain adequate levels of vitamin D solely from the diet. The current Dietary Reference Intake (DRI) is 400 IU (or 10 µg) per day for adults over age 50, 600 IU (15 µg) for adults over age 70, and 200 IU (5 µg) for all other adults and children.[33] Some researchers recommend an even higher dose of 800 IU (20 µg) per day for older adults (Table 1).[34] Each day, one would need to eat approximately 25 to 100 g of fatty, oily fish to obtain the daily requirement of vitamin D. Eating 25 g of sardines provides between 7 and 10 mg of vitamin D; other fatty, oily fish generally provide much lower amounts.[35] Besides these fish, most other foods naturally provide little or no vitamin D (Table 2).

Because of the limited natural sources of vitamin D, the United States government chose to fortify milk to prevent rickets.[36,37,38,39,40] Other dairy products, such as cheese, yogurt, ice cream, and cottage cheese, are typically not fortified. As long as whole milk is drunk daily in quantity (each cup should provide at least 100 IU), this method works relatively well. However, much of the world's populations cannot process lactose after weaning from the breast.[41,42,43] High rates of lactose malabsorption occur among populations in Asia and Africa, among Native Americans in North and South America, and among southern Europeans.[44] Therefore, while a goal of achieving adequate levels of vitamin D through fortification of milk may be attainable for those of northern European ancestry, even in this group few individuals actually consume the requisite amount of milk each day to meet the DRI of vitamin D. Of further concern, one group of researchers found that up to 70% of milk containers sampled had less than the stated value of vitamin D.[45,46,47] In addition, consumers are increasingly switching to lower fat versions of milk. In one report,[45] three of 14 skim milk containers sampled had no measurable vitamin D, while another study[48] found that up to 47% of skim milk samples contained 0% to 50% of the amount of vitamin D claimed on the label, underscoring the fact that skim milk may be an inadequate source of vitamin D.[45]

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