A new dose-response trial published in the American Journal of Nutrition found that a vitamin D intake above 1,200 IU is needed for teenagers to achieve a vitamin D status of 20 ng/ml or greater.
The required vitamin D intake for optimal health poses a heated debate. The current recommended daily allowance (RDA) for vitamin D is set at a meager 600 IU. The RDA was created with the primary goal of achieving a vitamin D status of 20 ng/ml or higher, a level considered adequate for bone health. However, the RDA fails to acknowledge the benefits gained from vitamin D above and beyond bone health.
Until recent years, vitamin D has been known for its role in bone health. Vitamin D promotes calcium absorption and maintains adequate calcium and phosphate concentrations, enabling normal mineralization of bone. In the past decade, researchers have begun to discover that vitamin D plays a role in many different areas of health, including the immune and cardiovascular system. In fact, studies have supported a vitamin D status above 30 ng/ml to provide protection from various diseases and conditions, such as breast and colorectal cancers. In addition, research shows that maintaining a vitamin D status of 45 ng/ml or higher is required for a mother to supply their infant with enough vitamin D through their breast milk to prevent rickets.
Despite popular belief, dietary sources do not provide adequate amounts of vitamin D. Thus, humans must rely on sun exposure or vitamin D supplementation to maintain sufficient levels. Since today’s society lives a primarily indoor lifestyle and many fear the sun, we now face a vitamin D deficiency pandemic. Over one third of the world’s population is considered vitamin D deficient. Because of this, researchers have taken an interest in evaluating the dose required to reach a status of 20 ng/ml.
In 2014, two statisticians reviewed the data on vitamin D intake and vitamin D levels. Based on this data, they concluded that 8,895 IU daily is required to get the 97.5% of the adult population above 20 ng/ml. GrassrootsHealth conducted a similar study and found that 7,000 IU daily was required to achieve 20 ng/ml in 97.5% of the population, which is not substantially different from the dose calculated previously.
Recently, researchers conducted a dose response, randomized controlled trial to determine the required vitamin D intake in white, healthy adolescents, ages 14-18 years, to achieve a status of 20 ng/ml. A total of 110 adolescents were randomly assigned to receive 0, 400 or 800 IU of vitamin D for 20 weeks during winter.
Here is what the researchers found:
- The average vitamin D levels increased from 19.7 ng/ml to 22.6 ng/ml and from 20.7 ng/ml to 25.6 ng/ml in the 400 IU and 800 IU groups, respectively (p < 0.001).
- The placebo group’s vitamin D status dropped from 18.7 ng/ml to 12.3 ng/ml (p < 0.001).
- In order to maintain a vitamin D status above 20 ng/ml among 90% of adolescents, a daily dose of 1,112 IU was required.
- Since there were not enough individuals who obtained a vitamin D status above 20 ng/ml, the researchers estimated the required vitamin D intake to achieve a vitamin D status of 20 ng/ml as greater than 1,200 IU daily.
The researchers concluded,
“Vitamin D intakes of between [400 and 1,200 IU daily] are required by white adolescents to maintain 25(OH)D concentrations > [10-20 ng/ml] during the winter…Such data allow for the ongoing refinement of vitamin D intake requirements for adolescents.”
While reviewing these findings, there are several important factors to note. First, a dose of 1,200 IU daily was required to achieve a vitamin D status of merely 20 ng/ml in 97.5% of the population. Remember, this status allows for optimal bone health, but research has found levels above 30 ng/ml provide additional benefits, potentially reducing one’s risk of cancer, among other diseases. Second, the study sample consisted of white adolescents. Due to a lighter skin pigmentation, white individuals are able to receive vitamin D from sun exposure at a much faster rate than individuals with darker skin pigmentation. Therefore, white adolescents face a lower risk of vitamin D deficiency than adolescents with darker skin pigmentation. Adolescents likely require less vitamin D than adults as their weight tends to be lower than adults. Lastly, the vast majority of the participants (81%) were of healthy weight. Obese and overweight individuals require higher vitamin D intakes than those who are of healthy weight.
The study provides some insight regarding the requirement of vitamin D intake for adolescents, proving once again that the RDA is significantly lower than it should be. However, we are left wondering how much vitamin D is required to achieve a vitamin D status above 30 ng/ml or 40 ng/ml among adolescents.
The Vitamin D Council recommends that adults supplement with 5000 IU daily when they are unable to receive safe, sensible sun exposure. Children should supplement with 1,000 IU per 25 pounds of body weight, applying to children who weigh up to 125 pounds.
Tovey, A. & Cannell, JJ. How much vitamin D do adolescents need? The Vitamin D Council Blog & Newsletter, 2016.
Smith, T. et al. Estimation of the dietary requirement for vitamin D in adolescents aged 14–18 y: a dose-response, double-blind, randomized placebo-controlled trial. The American Journal of Clinical Nutrition, 2016.