Misinterpretations of blood tests for vitamin D often lead patients to wrongfully think they have vitamin D deficiency, leading them to take vitamin supplements unnecessarily, according to a recent study published in The New England Journal of Medicine.
The perspective article, “Vitamin D Deficiency — Is There Really a Pandemic?,” shows that, contrary to what some think, vitamin D deficiency is far from pandemic, with only six 6 percent of Americans ages 1 to 70 deficient for the vitamin.
Vitamin D is essential for strong bones, because it helps the body use calcium from the diet. Traditionally, vitamin D deficiency has been associated with skeletal deformities, but recent research is underscoring the importance of vitamin D in other health conditions, from cardiovascular disease and cognitive impairment to cancer, including prostate cancer. In fact, some studies suggest that vitamin D can regulate the immune system to prevent prostate cancer initiation and progression.
Too much vitamin D, however, can also cause health problems. High levels of vitamin D increase the concentration of calcium in the blood, causing such conditions as nausea, constipation, abnormal heart rhythms, and kidney stones.
Researchers at the Institute of Medicine of the National Academies in the U.S. set a recommended dietary allowance, or RDA, that established the daily requirements of vitamin D. By comparing vitamin D intake and blood levels with bone health, they estimated that infants up to 12 months need about 400 international units of vitamin D per day, those between ages 1 and 70 need 600 daily units, and those over 70 require 800 daily units of vitamin D.
In setting the RDA, they tried to ensure that everyone gets enough vitamin D, putting it at the high end of the spectrum of the population’s needs — 600 to 800 units. But this has led to many misinterpretations.
“A common misconception is that the RDA functions as a ‘cut point’ and that nearly the entire population must have a serum 25(OH)D [vitamin D metabolite in the blood] level above 20 ng per milliliter to achieve good bone health,” the researchers wrote. “The reality is that the majority (about 97.5%) of the population has a requirement of 20 ng per milliliter or less.”
Many people and their doctors see this number as a threshold that everyone needs to be above, the researchers said, leading to an increase in vitamin pill use from 5 percent in 1999 to 19 percent in 2012.
“Clearly, this approach misclassifies as ‘deficient’ most people whose nutrient requirements are being met — thereby creating the appearance of a pandemic of deficiency,” they wrote.
But, according to the researchers, only 6 percent of Americans are actually deficient for vitamin D, and 13 percent are at risk of not getting enough, meaning that most Americans taking vitamin D supplements are taking unnecessary, and potentially harmful, pills.
“Although clinical judgment and customized interventions can be used with individual patients, avoidance of overscreening and overprescribing of supplemental vitamin D remains important,” they concluded.