The review,¹ “Rickets: Not a Disease of the Past,” by Nield and colleagues in this issue of American Family Physician is an important reminder that changes in lifestyle can cause the reappearance of disease states that were thought to have been eradicated. In one study more than 80 years ago, one teaspoon of cod liver oil given daily to children was found to prevent and, in many cases, reverse nutritional rickets²; this finding was a major scientific discovery that is still relevant today. The advent of modern-day laboratory techniques that allow isolation and measurement of vitamin D compounds³ has shown that one teaspoon of cod liver oil provides 400 IU of vitamin D₃, which appears to be an adequate amount for infants and young children.⁴

During the past two decades, the lifestyles and dietary habits of Americans have changed considerably. The average American spends 93 percent of his or her time indoors⁵—more time spent in front of the television, the video game console, or the computer. Children with lighter pigment who are encouraged to play outdoors often are covered with sunscreen during the summer months, preventing the synthesis of previtamin D₃ in their skin ⁶ and making them more susceptible to vitamin D deficiency during winter months, especially in northern climates. Children with darker pigment require much greater sunlight exposure to attain the same levels of vitamin D₃.⁷

Intake of foods enriched with vitamin D, such as vitamin D–fortified cow’s milk and yogurt, provides relatively small amounts of vitamin D. One cup of milk provides 100 IU of vitamin D₃, whereas 10 minutes of full-body sunlight exposure during summer months provides 10,000 to 20,000 IU of vitamin D₃ within 24 hours³ The American Academy of Pediatrics (AAP), however, does not recommend sun exposure before six months of age and advises parents to apply sunscreen to infants when exposed to the sun to avoid skin damage. As a result, the AAP recognizes that using sunlight as the main source of vitamin D for infants is not a viable option.

An issue with breastfeeding is that when the mother is deficient in vitamin D, her milk has limited transfer of vitamin D and its metabolites. Consequently, unless her infant receives ultraviolet exposure from sunlight or receives supplements, the infant will be vitamin D deficient.³ The AAP recommends that all infants, including those who are exclusively breastfed, receive a minimum of 200 IU of vitamin D per day, starting within the first two months of life. This recommendation ensures that the breastfed infant will have adequate vitamin D status⁸ but does not address the reason the breast milk is deficient.

The effectiveness of high-dose vitamin D supplementation in lactating women has been studied in two pilot clinical trials.^9,10 Both studies demonstrate that if the mother has substantial circulating levels of vitamin D₃ and 25(OH)D₃, her breast milk will have consistently higher antirachitic activity, and her infant will achieve optimal vitamin D status. Before this therapy can be recommended for all breastfeeding mothers and infants, larger studies need to be completed.

Only recently have liquid forms of vitamin D₃ (cholecalciferol) become available commercially. Vitamin D₃ is the more bio- available form of vitamin D; vitamin D₂ is less potent than vitamin D₃¹¹ As noted by Nield and colleagues,¹ all infants should receive a dietary source of vitamin D₃ that equals at least 200 IU per day, through a supplement if breastfeeding or through formula for those not breastfeeding.

The long-term implications of vitamin D deficiency are not restricted to bone disease because multiple disorders have been linked with vitamin D deficiency. For example, patients with cystic fibrosis experience the sequelae of vitamin D deficiency because of their malabsorption of fats and fat-soluble vitamins. In December 2005, the Cystic Fibrosis Foundation released a consensus statement¹² calling for all physicians who have patients with cystic fibrosis to measure their vitamin D levels and recommend supplementation for those who are deficient to help normalize bone mineral density. Vitamin D deficiency is common in persons with cystic fibrosis irrespective of season or latitude. What was once thought to be rare is, in fact, common.

For this and other reasons, optimization of vitamin D levels is viewed as an important factor in long-term health. Through enhanced awareness, it is eminently possible to prevent rickets and other conditions caused by vitamin D deficiency in the 21st century.