In an ancillary study from the results of the Vitamin D and Omega-3 Trial (VITAL), one of the largest human clinical trials in history on both vitamin D and omega-3 supplementation, researchers noted that there were no significant associations between vitamin D consumption and bone fracture risk among the population, which was comprised of men over the age of 50 and women over the age of 55.
 
Participants of VITAL were not recruited on the basis of vitamin D deficiency, low bone mass, or osteoporosis, and incident fractures were reported by participants on annual questionnaires, with following medical review.
 
Among 25,871 participants, 1,991 incident fractures were confirmed in 1,551 people over a mean follow-up period of 5.3 years. With 769 participants in the vitamin D group and 782 placebo group having experienced a fracture during the study period, there were no significant associations between vitamin D supplementation and incident fracture risk, nonvertebral fractures, or hip fractures. There were no substantial between-group differences in adverse events including fractures, including characteristics such as age, sex, race, ethnic group, body-mass index, or blood concentrations of vitamin D.
 
“Vitamin D3 supplementation did not result in a significantly lower risk of fractures than placebo among generally healthy midlife and older adults who were not selected for vitamin D deficiency, low bone mass, or osteoporosis,” the authors concluded.
 
In an accompanying editorial Steven R. Cummings, MD, and Clifford Rosen, MD, wrote, “VITAL and this ancillary study show that vitamin supplements do not have important health benefits in the general population of older adults, even in those with low 25-hydroxyvitamin D levels,” citing a number of other ancillary studies concluding that vitamin D did not have significant associations with cancer, cardiovascular disease, and a number of other diseases. VITAL concluded that there was a 25% reduction of cancer risk when excluding the first two years of follow-up, though accounting for all five years did not result in a significant association between vitamin D and cancer.  
 
However, Cummings and Rosen note that in the 20% of participants who took supplemental calcium, vitamin D supplementation was not significantly associated with a reduced risk of fractures over the median follow-up period. However, the authors wrote that for those suffering from hypocalcemia, the potential benefits of vitamin D remain uncertain. “More than 10 million serum 25-hydroxyvitamin D tests are performed annually in the United States. Results from these tests often include the classification of vitamin D “insufficiency” (<30 ng per milliliter) and “deficiency” (<20 ng per milliliter), prompting vitamin D supplementation. In this ancillary study and other VITAL studies, no subgroups defined according to baseline 25-hydroxyvitamin D level, even below 20 ng per milliliter, benefited from supplements. Thus, there is no justification for measuring 25-hydroxyvitamin D in the general population or treating to a target serum level,” the authors wrote, noting that the use of the terms vitamin D “insufficiency” and “deficiency” should now be reconsidered.
 
“The fact that vitamin D had no effect on fractures should put to rest any notion of an important benefit of vitamin D alone to prevent fractures in the larger population.”
 
No Control for Calcium Presents a Glaring Limitation
 
According to Andrea Wong, PhD, senior vice president of scientific and regulatory affairs for the Council of Responsible Nutrition (CRN), it is not surprising to see that a causal link couldn’t be established given that the VITAL researchers did not account for calcium intake among the participants.
 
“Vitamin D and calcium work in tandem to support bone health—calcium helps build and maintain bones, while vitamin D helps your body effectively absorb calcium,” Wong said. “So, these secondary study results are not surprising since VITAL was designed to assess vitamin D supplementation alone and did not include or control for calcium supplementation and intake. It seems obvious that investigating one without the other would produce disappointing results.
 
“Further, the study focused only on generally healthy midlife or older adults instead of individuals with vitamin D deficiency, low bone mass, or osteoporosis who may be more vulnerable to fractures and derive a benefit from vitamin D supplementation. The odds were stacked against this ancillary study before it even started.”
 
Despite the limitations of the ancillary study, VITAL yielded promising results for vitamin D’s impact on cancer-related death and autoimmune diseases, which the accompanying editorial to the ancillary study ignored, Wong said. She noted that advising that the general population should not supplement with vitamin D despite recorded widespread inadequacies is concerning.
 
“The fact remains that vitamin D is an essential nutrient that supports numerous biological functions,” Wong wrote. “Dietary studies have repeatedly shown many people still fall short of obtaining adequate levels of vitamin D and may be missing out on health benefits. The most recent Dietary Guidelines for Americans identifies vitamin D as a ‘nutrient of public health concern.’ Advising people to stop taking vitamin D supplements when natural food sources of this nutrient are scarce and sun exposure may not be feasible for those who are most vulnerable, is a disservice to public health.
 
“People should discuss with their healthcare practitioner whether testing their vitamin D levels or supplementing with vitamin D is appropriate.”