Although it is estimated that at least one in three American adults 60 and older takes vitamin D supplements, a gold-standard study of almost 26,000 men and women in their 50s, 60s, and 70s has now indicated that they offer no protection against bone fractures. This news, published in the New England Journal of Medicine in July, follows earlier evidence from the same group of 26,000 people that supplemental vitamin D offers no protection against a number of other ills.
The study from which the findings have sprung is called VITAL (VITamin D and OmegA-3 TriaL). A Harvard-led investigation, it was originally set up to see whether vitamin D and/or omega-3 fatty acids might protect against cancer and heart disease in middle-aged and older adults. Almost 13,000 healthy participants were assigned to take 2,000 International Units of vitamin D every day (in some cases with fish oil), while another 13,000 took a placebo. All participants were followed for an average of 5.3 years. The study was double-blinded: Neither the subjects nor the investigators knew who was taking what, which strengthens the results. Vitamin D turned out not to protect against cancer, heart attacks, strokes, or cardiovascular death.
Since these findings were published in 2018, the researchers have looked into other health outcomes for the same set of participants to see if vitamin D might have protected against other conditions. So far, they’ve found, it did not ward off depression or chronic knee pain, decrease the risk of macular degeneration, reduce migraine frequency, or improve cognitive function.
Now, this latest of VITAL’s ancillary studies has determined that vitamin D supplements are no more likely than a “sugar pill” to stave off a fracture in the spine, hip, or anywhere else in the body, even though vitamin D is necessary for optimal calcium absorption. The result held true whether or not the participants also took calcium supplements and even if their blood samples initially showed insufficient or deficient levels of vitamin D. “Insufficient” is often considered anything less than 30 nanograms per milliliter of blood, while “deficient” is anything less than 20.
Additionally, the finding held up regardless of gender or whether the person had previously suffered a fracture or been diagnosed with osteoporosis.
An editorial accompanying the latest study goes so far as to say that the results are so strong, there is no justification for measuring vitamin D blood levels in the general population or targeting a certain threshold to reach. Currently, measurements of vitamin D are Medicare’s seventh top expense for lab tests. In 2019, Medicare spent almost $300 million on them, more than it spent on tests for hemoglobin A1C levels (which check for diabetes), PSA levels (which check for prostate cancer), and blood iron levels. But this study suggests that 20 nanograms—the level at which a doctor might advise a patient to start taking vitamin D supplements—is not a telling cutoff point, at least not when it comes to bone health.
Some previous studies have shown that vitamin D supplementation provides a modest benefit in helping people avoid fractures. But last year, a comprehensive review of the literature by the U.S. Preventive Services Task Force concluded that there was no effect of supplemental vitamin D on fracture incidence in people with low blood levels of the nutrient.
The VITAL study did not control for every possible factor that might affect bone health. For instance, the participants’ level of physical activity, a known bone strengthener, was not accounted for. Nor were consumption levels or blood levels of such bone-protecting nutrients as the mineral magnesium and trace elements such as boron. Other factors that could have shed light on the impact of vitamin D supplementation were not assessed, either, including whether the participants had osteoporosis to begin with.
“Bone health is a team sport that involves not just nutrition and lifestyle but also the medications people take regularly and their genetic predisposition,” comments Ed Blonz, Ph.D., an assistant clinical professor in the School of Pharmacy at the University of California, San Francisco, and a member of our editorial board. In other words, many potential factors were not measured.
Then, too, while people as young as 50 were included in the study, the average age was 67, so it is possible that the results would have differed for people younger than 50.
No study is perfect, but this one is about as well conducted and thorough as they come. Still, the results don’t mean vitamin D supplements should never be considered. If you’re healthy in general, the decision to take vitamin D for bone health is a reasonable one to discuss with your doctor, especially if there are factors that limit how much vitamin D you are getting. For instance, much of our vitamin D comes not from food but from exposure to sunlight, so someone living in an institutionalized setting with little or no exposure to sunlight—or at higher latitudes where sunlight may be insufficient during winter months—might benefit from vitamin D supplementation. So might people who have malabsorption issues (such as Crohn’s or celiac disease), those who are already receiving treatment for osteoporosis, and those who get little vitamin D in their diet.
Whatever the individual decision, based on the latest results, the blood level that should be considered as the dividing line between “enough” and “not enough” when it comes to taking vitamin D to prevent fractures probably needs to be reconsidered.