Opinion: Vitamin D Panel Misses the Mark on Deficiency

By Woodson Merrell, M.D.

The IOM report on calcium and vitamin D questioned what’s accepted as state-of-the-art thinking on what constitutes a vitamin D deficiency. This is a key point because the amount of vitamin D a person takes above and beyond the new Daily Recommended Intake of 600 international units should be based on whether they have a measurable deficiency or not, which is determined by how much of the vitamin is stored in their body. [D is stored mainly in fat cells, and most accurately established by measuring circulating blood levels of 25-hydroxyvitamin D or 25(OH)D.] The new IOM report sets the “normal” range for 25 (OH) D at 20-30 nanograms/milliliter, back to levels that were established when the test was first developed 3 decades ago. But I will not adapt this new recommendation.25-hydroxyvitamin D: Doctors must measure 25 (OH) D levels in the blood to establish a deficiency.

When scientists first set the normal D range thirty years ago, they lacked accurate tools for gauging a deficiency, and so they rather simplistically measured 25 (OH) D levels of people who had no symptoms of deficiency, using those levels to set the bar for what was considered healthy. Now, we have the capability of looking at functional biomarkers (biochemical indicators that the vitamin is doing its job) such as parathyroid hormone, calcium absorption, and bone mineral density. Based on voluminous research  spearheaded by one of the world’s leading experts, Bruce Hollis PhD, scientists have more accurately defined vitamin D deficiency as circulating 25 (OH) D levels of less than 32 nanograms. That’s what I look for when I counsel my patients on D supplements. 

The amount of D a person takes beyond the new minimum of 600 international units (and maximum of 4,000) is best  determined by the blood test--not by guesswork. In my opinion, the IOM panel, while correct in tripling the minimum daily dose and doubling the maximum safe dose, has missed the mark in determining what constitutes a deficiency that necessitates additional vitamin D supplementation.