Vitamin D is in the news a lot in 2017, mostly in stories that suggest “more is better.” But vitamin D has been of interest to the public since the 1920s, when its role in preventing the childhood bone disorder rickets was first understood.
RDA, DRI, and IUs: What’s the Difference?
Recommended Dietary Allowances (RDA) is an old term. The Food and Nutrition Board of the US Institute of Medicine (IOM) now uses nutrient reference values entitled Dietary Reference Intakes (DRI). These include RDAs in some cases and “Adequate Intakes” (AIs) in others where evidence is weaker. The vitamin D DRI is listed as AIs. They are expressed in micrograms per day, which can be converted to International Units, IUs (5 mcg vitamin D is equivalent to 200 IU). The AI for vitamin D is 200 to 400 International Units (IU) each day.
Many expert panels make recommendations that differ from the Board’s, and usually express the recommendations in IUs. The Board is currently studying its vitamin D recommendations and is expected to raise them.
It’s too simple to ask for a single recommendation for all ages and groups of people. The best minimum intake is different for different groups.
In recent years, the American Academy of Pediatrics doubled their recommendation for vitamin D intake in children, from 200 IU to 400 IU every day, starting a few days after birth. And babies will not likely get that amount from breast feeding. In the 1920s and 30s, before widespread use of formula feeding, parents knew to put babies in the sun to prevent the devastating product of vitamin D deficiency, rickets, a condition of deformed bones.
But extensive sun exposure can harm skin, and is not available in the winter in most regions, so mothers needed to provide nutritional supplements. The benefits of vitamin D from cod liver oil became known in the 1930s. Cod liver oil became a popular, if not tasty, children’s supplement. (Cod liver oil is a good source of vitamin D, but it also has abundant vitamin A, and too much can easily cause serious vitamin A toxicity.)
Adolescents may benefit from ten times the old recommendation, that is, from 2000 IU each day, and it is generally safe at that dose, according to at least one study. (Journal Clinical Endocrinology Metabolism).
Studies show that the vitamin D levels in many older women are below recommended levels. It’s even a problem in men. A study of older men in North America found one in four deficient in vitamin D, and most men had very low vitamin D intake, if not clearly deficient by old standards. (Journal of Clinical Endocrinology & Metabolism)
The Society of Obstetricians and Gynaecologists of Canada now recommends supplementation with 800 IU/d of vitamin D each day. (Journal Obstetrics Gynaecology Canada S34-41)
The American Geriatrics Society currently recommends adults should consume at least 400 IU of vitamin D daily. It’s generally expected that the AGS will greatly increase their vitamin D intake recommendations.