Are You D Deficient?
In “Vitamin D: What’s the ‘right’ level?” Harvard Health Blog contributing editor Monique Tello, MD, MPH writes that many of her patients who come into the office for physical exams ask to have their vitamin D levels checked. They may have a family member with osteoporosis, or have even had bone thinning themselves. All seem to want to know that they’re doing everything they can to keep their bones strong. Vitamin D is critical for healthy bones. But when physicians check blood levels for vitamin D, precisely how to act on the result is still the subject of great controversy.
What is a “healthy” vitamin D level?
What is the current threshold at which vitamin D levels are considered low? The answer is not just academic, as too low a level puts people at risk for developing bone thinning and increased fracture risk. To be clear, the measure is for blood level of 25-hydroxy-vitamin D, most commonly quantified in nanograms per milliliter (ng/mL).
In 2010, the Institute of Medicine reported on a thorough examination of the data that estimated a vitamin D level of 20 ng/mL or higher was adequate for good bone health, and a level below 20 was considered a vitamin D deficiency.
Dr. Tello observes that in clinical practice it is not uncommon to see a vitamin D level less than 20. When that happens, she writes, doctors often tell patients that they are deficient and recommend fairly aggressive replenishment, as well as ongoing supplementation. As she describes it, “The majority of folks have a level between 20 and 40, in my experience, and this is corroborated by the IOM’s findings in that 2010 report.”
But in 2011, the Endocrine Society—an international medical organization founded in 1916 that monitors the field of endocrinology and metabolism—issued a report urging a far higher minimum blood level of vitamin D. The society’s clinical practice guideline was developed by experts in the field assigned to a vitamin D task force, and they concluded: “Based on all the evidence, at a minimum, we recommend vitamin D levels of 30 ng/mL, and because of the vagaries of some of the assays, to guarantee sufficiency, we recommend between 40 and 60 ng/mL for both children and adults.”
And yet the most recent opinion on the right target level of vitamin D is presented in an article published in NEJM. In this piece, entitled, “Vitamin D Deficiency: Is There Really a Pandemic?”, several of the leading epidemiologists and endocrinologists who were on the original IOM committee argue for a lowering of the currently accepted threshold level of 20, stating that the level they estimated as acceptable was never intended to be used to define vitamin D deficiency. They feel that clinicians are overscreening for vitamin D deficiency, and unnecessarily treating individuals whose levels are perfectly acceptable.
Based on this analysis, a more appropriate threshold for vitamin D deficiency would be a much lower 12.5 ng/mL. The researchers examined a massive amount of data from the National Health and Nutrition Examination Survey (NHANES) for 2007 through 2010, and found that less than 6% of Americans had vitamin D levels less than 12.5. And so a threshold of 12.5 ng/mL would most certainly eliminate the “pandemic” of vitamin D deficiency.
What is and isn’t vitamin D deficiency
Tello spoke with osteoporosis expert Dr. Joel Finkelstein, associate director of the Bone Density Center at Massachusetts General Hospital, whose research in this field spans over three decades. He agreed with the authors of the NEJM article that we are currently overscreening for vitamin D deficiency, and overtreating people who are getting enough vitamin D through diet and sun exposure. “Vitamin D has been hyped massively,” he told her. “We do not need to be checking the vitamin D levels of most healthy individuals.”
He points out that from an evolutionary standpoint, it doesn’t make sense that higher vitamin D levels would be beneficial to humans. Finkelstein reminds us that “vitamin D is actually quite hard to find in naturally occurring food sources. Yes, we can get vitamin D from the sun, but our bodies evolved to create darker skin in the parts of the world that get the most sun. If vitamin D is so critical to humans, why would we evolve in this way, to require something that is hard to come by, and then evolve in such a way as to make it harder to absorb?”
Who should be screened for vitamin D deficiency?
Dr. Finkelstein and his colleagues recently published a study of over 2,000 perimenopausal women who had been followed for almost 10 years, and they found that vitamin D levels less than 20 were associated with a slightly increased risk of nontraumatic fractures. They concluded that because few foods contain vitamin D, vitamin D supplementation is warranted in women at midlife with levels less than 20 ng/mL. “For perimenopausal women or other groups of people with higher fracture risk, certainly a level of 20 or above is ideal,” he says, adding that “for the vast majority of healthy individuals, levels much lower—15, maybe 10—are probably perfectly fine, and so I would say I agree with what the authors [of the NEJM article] are saying.”
Dr. Tello points out that most experts, including Dr. Finkelstein, agree that physicians should be checking vitamin D levels in high-risk people, such as patients with anorexia nervosa, people who have had gastric bypass surgeries, those who suffer from other malabsorption syndromes like celiac, or who simply have dark skin or wear total skin covering (and thus absorb less sunlight).
In addition to perimenopausal women and the high-risk groups mentioned above, other patient populations that likely require a 20 ng/mL vitamin D level include people diagnosed with reduced bone density short of osteoporosis, those with osteoporosis or other skeletal disorders, and pregnant and lactating women. All of these groups should be screened and treated appropriately.