- Kenny Lin, MD, MPH
For as long as I can remember, throughout medical training and clinical practice, the message from my mentors and colleagues about vitamin D supplements was the same: the sooner patients started taking them, the better to prevent osteoporosis and fractures later in life. And that wasn't the only benefit: in 2012, the U.S. Preventive Services Task Force even recommended vitamin D supplementation in community-dwelling adults age 65 and older to prevent falls.
But the very same Task Force soon began to raise doubts about the value of vitamin D supplements. In 2014, it found insufficient evidence to recommend calcium and vitamin D to prevent fractures in premenopausal women or men, and recommended against postmenopausal women using daily vitamin D supplements containing 400 IU or less because these increased the risk of kidney stones without affecting fracture rates. What about a strategy of selective supplementation in vitamin D "deficient" persons? The USPSTF also found insufficient evidence that screening for vitamin D deficiency in adults improves health outcomes, and the American Society for Clinical Pathology recommended against screening for vitamin D deficiency in the Choosing Wisely campaign.
So what is vitamin D supplementation good for? Recognizing the vitamin D deficiency in older adults has been associated with functional decline, Dr. Heike Bischoff-Ferrari and colleagues recently performed a randomized controlled trial comparing high-dose (60,000 IU per month or 24,000 IU per month plus calcifediol, a liver metabolite of vitamin D) to low-dose (24,000 IU per month) vitamin D supplements in 200 community-dwelling men and women 70 years and older with a history of falls. After 12 months, participants receiving the high-dose supplement did not have better lower extremity function and were more likely to have experienced falls than participants in the low-dose group. The authors of an accompanying editorial noted that after many similar trials, vitamin D supplementation has only been shown to reduce fractures and falls in institutionalized older adults.
Putting this all together, the next time a healthy adult of any age asks me if he or she should be taking a vitamin D supplement, I plan to answer: we don't know for sure, but probably not - and we don't need to know what your vitamin D level is, either.