At the turn of the new millennium, a set of rather shocking reports were published suggesting that wide swaths of the global population were chronically vitamin D deficient1. These reports provoked public health campaigns to raise awareness about vitamin D deficiency, to increase serum vitamin D testing, and to advocate for vitamin D supplementation. Parents, who had only recently accepted the idea that it was best to keep their children out of sunlight for risk of cancer, were now expected to make sure their kids played outdoors enough to get adequate amounts of sunlight and vitamin D.
The roots of this radical public health change are now somewhat murky, but the effect is irrefutable. Between 2000 and 2010, the number of serum vitamin D tests paid for by Medicare part B increased by almost 2 orders of magnitude.2 Over the same decade, the number of people taking a vitamin D supplement of ≥1,000 IU per day increased more than 30-fold, from 0.3% in 2000 to 9.4% in 2010. The rate doubled again by 2014, with 18.2% of people taking high-dose vitamin supplement. Most shockingly, 3% of the population was taking a supplement of at least 4000 IU per day of vitamin D in 2014.3
From these numbers, you would imagine that vitamin D deficiency is a national and perhaps worldwide epidemic. Moreover, you would have to imagine that vitamin D supplementation was saving countless people from developing osteoporosis, heart disease, or any of the other ailments that befall people with chronic vitamin D deficiency. Dr. Kenneth Lin points out in an editorial for American Family Physician, not only is true vitamin D deficiency far less prevalent than once imagined, vitamin D supplementation and hyper-supplementation provide no significant benefit.
In a review of over 100 systematic reviews of clinical studies on the topic, authors could identify only a few probable clinical benefits of vitamin D supplementation. In no case were the results terribly convincing. Notably, the conditions for which one would assume vitamin D supplementation would be beneficial, namely bone mineral density and fracture risk, were unaffected by vitamin D supplements.4 The U.S. Preventive Services Task Force cited “insufficient evidence” that vitamin D prevented cardiovascular disease, cancer, or fractures outside of institutionalized, elderly patients.5,6
Vitamin D supplementation is not without the risk. It is one of the four fat-soluble vitamins, and people consuming a total of 4000 IU per day (supplements and diet combined) risk hypercalcemia, endovascular calcification, and kidney disease.7 Even relatively modest daily supplementation with calcium and vitamin D significantly increases the risk of developing nephrolithiasis.8
While it is not always appreciated, not all levels of vitamin D deficiency are the same. While the laboratory may report a vitamin D level below the range of normal, supplementation is not required until levels fall well below the lower limit of normal. Specifically, the lower limit of normal for many serum 25-hydroxyvitamin D laboratory reports is 30 ng/mL (75 nmol/L). However, the Institute of Medicine maintains that 97.5% of people who have serum vitamin D levels above 20 ng/mL (50 nmol/L) are adequately protected from bone demineralization.9 Ironically, the(inappropriate application of the) Institute of Medicine’s 25-hydroxyvitamin D reference values contributed to over-supplementation.7,9
As Lin points out, it may be time to rethink when and how often we test for vitamin D deficiency. In most cases, the true cut off the deficiency is 20, not 30 ng/mL. Lastly, since vitamin D supplementation does not actually lead to robust clinical benefit, should we be universally recommending a not altogether innocuous supplement just because it is relatively inexpensive?
1. Sattar N, Welsh P, Panarelli M, Forouhi NG. Increasing Requests for Vitamin D Measurement: Costly, Confusing, and without Credibility. Lancet. 2012;379(9811):95-96. doi:10.1016/s0140-6736(11)61816-3
2. Shahangian S, Alspach TD, Astles JR, Yesupriya A, Dettwyler WK. Trends in Laboratory Test Volumes for Medicare Part B Reimbursements, 2000-2010. Arch Pathol Lab Med. 2014;138(2):189-203. doi:10.5858/arpa.2013-0149-OA
3. Rooney MR, Harnack L, Michos ED, Ogilvie RP, Sempos CT, Lutsey PL. Trends in Use of High Dose Vitamin D Supplements Exceeding 1,000 or 4,000 International Units Daily, 1999-2014. JAMA. 2017;317(23):2448-2450. doi:10.1001/jama.2017.4392
4. Theodoratou E, Tzoulaki I, Zgaga L, Ioannidis JPA. Vitamin D and Multiple Health Outcomes: Umbrella Review of Systematic Reviews and Meta-Analyses of Observational Studies and Randomised Trials. BMJ : British Medical Journal. 2014;348. doi:10.1136/bmj.g2035
5. Moyer VA. Vitamin D and Calcium Supplementation to Prevent Fractures in Adults: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2013;158(9):691-696. doi:10.7326/0003-4819-158-9-201305070-00603
6. Moyer VA. Vitamin, Mineral, and Multivitamin Supplements for the Primary Prevention of Cardiovascular Disease and Cancer: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2014;160(8):558-564. doi:10.7326/m14-0198
7. Del Valle HB, Yaktine AL, Taylor CL, Ross AC. Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press; 2011.
8. Jackson RD, LaCroix AZ, Gass M, et al. Calcium Plus Vitamin D Supplementation and the Risk of Fractures. N Engl J Med. 2006;354(7):669-683. doi:10.1056/NEJMoa055218
9. Manson JE, Brannon PM, Rosen CJ, Taylor CL. Vitamin D Deficiency — Is There Really a Pandemic? New England Journal of Medicine. 2016;375(19):1817-1820. doi:10.1056/NEJMp1608005