Vitamin D Deficiency in Teens
Health and Wellness
April 26, 2009
Necessary for bone mineralization, calcium absorption and the prevention of rickets, fat-soluble vitamin D is naturally present in few foods. Small amounts are found in beef liver, cheese and egg yolks. Fish oils are another good source. Once in the body, vitamin D is biologically inert and must be converted through a process called hydroxylation for use.
Serum concentration of 25(OH)D is the best indicator of vitamin D status, though there is currently a lack of consensus as to optimal levels. At the time the study was conducted, levels of less than 11 ng/mL (nanograms per milliliter) were classified as vitamin D deficient. Experts have since recommended raising this level to 20 ng/mL, or higher.
“While previous guidelines were based on the prevention of rickets, scientists have found that higher serum levels of vitamin D are necessary to achieve optimal bone mineralization throughout the lifespan,” says Dr. Linda Gerber, co-author of the study and Professor of Public Health and Medicine at Cornell.
Depending on the population and how deficiency is defined, Dr. Gerber, along with her colleagues, Drs. Saintonge and Bang, estimated deficiency to range in prevalence from two to 14%. Non-Hispanic black adolescents were at the highest risk, with a prevalence ranging from 11% to 50%. The risk of deficiency was more than double for females as compared with males; overweight teens had increased risk as compared with normal-weight teens. When the data were examined with minimum levels set at 30 ng/mL, an alarming 48% of adolescents were found to be deficient.
“Generally, milk had been the primary source of dietary vitamin D among children. Among adolescents milk consumption has been replaced by soft drinks, juice, and other beverages that are not fortified with vitamin D. Further, many teens from ethnic populations are lactose intolerant and avoid milk. Though there are other nutritional sources of vitamin D, many teens are eating foods that are low in nutritional value,” says Gerber.
Helping overweight teens achieve proper vitamin D levels presents a unique challenge. Vitamin D is fat soluble, so deficiency in this population may be magnified if the vitamin is hiding in body fat, limiting bioavailability. Oral doses approaching the upper limit of 2000 IU/day may be necessary for this group, says Gerber. And appropriate nutrition should be a longer-term goal.
Regional intake differences, due to sun exposure, have been studied in the past, but this study adjusted for these differences in their calculations. It is still interesting to note a possible association between inner-city adolescent populations and vitamin D deficiency, because of the dense concentration of buildings interfering with sunlight exposure. Seasonal differences exist as well. Deficiency, for example, tends to be more prevalent in the winter months.
Since harmful consequences of vitamin D deficiency develop over time, retailers need to focus on the adolescent population in their outreach programs, nutritional recommendations and in-store signage. Deficiency prevention, says Gerber, should begin in childhood.
“New evidence suggests that vitamin D deficiency may be associated with risk factors for many chronic diseases such as high blood pressure. Therefore, by studying the adolescent population, we may be able to prevent the progression to some of these,” she says.
Most of the vitamin D in the American diet is derived from fortified foods, according to National Institutes of Health. Orange juice, yogurt, breakfast cereals and milk are often vitamin D fortified with 100 IU/cup – 25% of the recommended American Academy of Pediatrics value. However, fortification may not be enough.
Gerber adds, “Using national data to quantify the scope of this problem will improve our ability to develop appropriate interventions to address deficiency among adolescents. These results also suggest that monitoring vitamin D should be much more consistently applied.”