Over the past few years, vitamin D rocketed from relative obscurity to high regard.
Primarily, excitement about the “sunshine-and-seafood” vitamin stemmed from strong links to cancer prevention — and its importance to bone health.
Vitamin D is clearly essential to bone health, primarily because the body needs it to get calcium into its bones.
But a new evidence review raises doubts about the value of vitamin D supplements for prevention of fractures among people with osteoporosis, or at risk for the disease.
Osteoporosis is the medical term for having porous and fragile bones. Osteoporosis affects more than 10 million Americans — 80% women — while another 34 million have osteopenia (low bone mass) which typically precedes osteoporosis.
Osteoporosis causes more than 1.5 million bone fractures annually in the United States — which typically occur in the hip, vertebrae, wrist, pelvis, or ribs.
Most public health authorities recommend calcium and vitamin D supplementation to protect against fractures, and the FDA authorized this health claim for supplement labels: “Adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life”.
Findings reported by the China-based authors of a new meta-analysis — a study that scrutinized data from 33 clinical trials — questions the value of calcium and vitamin D for preventing fractures.
How real are the doubts raised by this new meta-analysis?
To separate the medical wheat from the scientific chaff, we also examined prior research, plus critiques of the new analysis issued by public health organizations.
Prior support for the value of vitamin D versus fracture risk
While the new meta-analysis calls the value of vitamin D for fracture-prevention into question, some prior studies support their use for that purpose.
For example, Scottish researchers came to relatively positive conclusions when they reviewed the clinical evidence using the rigorous analytical techniques of the Cochrane Collaboration (Avenel A et al. 2014).
While they found little fracture-prevention benefit from supplemental vitamin D alone, they did find evidence favoring the value of supplemental vitamin D plus calcium:
It’s important to stress their caveat that vitamin D alone didn’t prevent fractures “in the formats and doses tested”.
Sadly — as is often the case with dietary supplement trials — many of the clinical studies reviewed by the Scottish team didn’t use doses high enough to raise blood levels into ranges considered optimal by leading vitamin D researchers.
And when University of Illinois scientists reviewed the evidence several years earlier, they found that calcium and vitamin D supplementation may — for some people — eliminate the need for bone-building pharmaceutical drugs.
Their analysis of 157 studies confirmed that people who raise their intake of calcium and vitamin D — either by dietary changes or supplementation — can boost their bone mineral density and reduce their risk for hip fracture significantly (Plawecki K et al. 2010).
New analysis casts doubt on calcium and vitamin D for preventing fractures
The authors of the new meta-analysis — published in the Journal of the American Medical Association — are orthopedists from China’s Tianjin Hospital.
They collected and analyzed data from 33 clinical trials that included 51,145 adults aged 50 years or older (Zhao J et al. 2017).
All the trials tested the ability of calcium, vitamin D — or the combination of the two — to reduce fracture rates among older adults living on their own (not in nursing homes or other residential care facilities).
Each trial included in the analysis compared the effect of calcium, vitamin D, or combination supplements versus a placebo or no treatment at all.
Most of the trials focused on hip fractures, because it’s one of the most common and high-risk complications of osteoporosis, but some examined the effects of vitamin D and/or calcium supplements on other fractures.
Overall, the authors found no evidence that calcium or vitamin D reduced the risk of hip fractures, compared either with placebo or with no treatment.
As they wrote, “… the use of supplements that included calcium, vitamin D, or both … was not associated with a lower risk of fractures ...”.
Their findings held true regardless of the dose levels of calcium or vitamin D, and regardless of a participant’s previous fracture history, gender, calcium intake, or baseline vitamin D levels.
The authors did note that because people living in nursing homes or other residential care facilities are known to be at higher risk for osteoporosis, they may benefit from calcium or vitamin D supplementation.
Health organizations issued key caveats and critiques
To put these latest results in a larger context, we reviewed the responses issued by four groups.
Each of these organizations is focused on bone health and nutrition. They include three nonprofit medical organizations, and the leading supplement trade association.
National Osteoporosis Foundation (NOF) response
In their response, the NOF echoed the Chinese team’s own caveat that the analysis included only clinical trials involving people living on their own, not those diagnosed with osteoporosis or living in care facilities, who are known to be at higher risk for fractures.
In addition, the NOF noted that people who aren’t deficient in calcium and/or vitamin D are unlikely to benefit from supplementation, and that baseline vitamin D levels were not measured in all study participants, making it impossible to make a definitive statement.
Lastly, they note that the new meta-analysis looked in part at patients who took vitamin D and/or calcium supplements for fewer than six months, which the NOF regarded as not long enough to reduce fracture risks.
By contrast, their own rigorous analysis of randomized trials in 2015 found “a significant risk reduction in fractures with calcium and vitamin D”, and “strongly suggested that calcium plus vitamin D supplementation in select populations can significantly reduce the risk of total fractures by 16% and hip fractures by 32%.”
The American Society for Bone and Mineral Research (ASBMR) response
This leading scientific organization for bone health experts urged patients and physicians to exercise caution regarding the new findings.
Like the NOF, they stressed that the study didn’t include adults over 50 living in hospitals, nursing homes or other facilities, who are at greater risk for osteoporosis and fractures.
In many ways, this study merely underscores current recommendations – for generally healthy adults over 50 living in the community, people should strive to get calcium from foods such as milk, vegetables, fruits and bean products, and vitamin D from foods and daily exposure to sunlight.
Vitamin D Council response
This nonprofit organization was founded by John Cannell, M.D.
His goal was to publicize widespread vitamin D deficiency and insufficiency, compared with fast-growing evidence linking vitamin D to a wider range of health benefits than previously recognized.
The Council’s response to the new meta-analysis was penned by Executive Director Melissa Sturges, and reviewed by Dr. Cannell.
As Ms. Sturges noted, a German study found that the bones in 25% of the 675 cadavers biopsied for the study displayed osteomalacia, or bone softening — which is almost never picked up on X-rays.
Crucially, the German researchers found that osteomalacia was more common in cadavers showing low vitamin D levels (Priemel M et al. 2010).
Sturges also noted that population studies among people with poor bone mineral density consistently link vitamin D deficiency with an increased risk for bone fractures.
And, as Sturges said, most of the studies included in the Chinese meta-analysis supplied their participants with 400-800 IU (10-20 mcg) of vitamin D per day — dose levels unlikely to enable the average adult to reach vitamin D sufficiency (40-80 ng/ml).
In addition, several of the clinical trials included in the analysis employed injected “bolus” doses of vitamin D, ranging between large doses every 1-3 months to a single dose of 300,000-500,000 per year.
However, prior research has shown that bolus dosing is not as effective as daily dosing at improving one’s vitamin D levels.
People who received large, bolus doses of vitamin D would only experience an increase in vitamin D levels for a few weeks before levels would begin to decline — which makes it hard to determine the relationship between vitamin D status and fracture risk over time.
Ms. Sturges also noted that a variety of factors affect bone health, and that vitamin D alone cannot prevent age-related bone loss or reverse the damage once it’s occurred.
She acknowledged that clinical trials testing the ability of vitamin D supplements to reduce fracture risk have yielded conflicting findings.
But as she said, “Bone health is contingent not only on vitamin D and calcium but also on magnesium intake (which is deplorable in many Americans), zinc intake, vitamin K intake and even silica intake.”
(Ms. Sturges could also have highlighted the need for potassium, boron, magnesium, and omega-3 fatty acids, all of which play important roles in bone health. See Mighty Magnesium for Bones, Hearts, Mood, & More, Omega-3s Seen as Stellar Bone-Builders, Omega-3 Breast & Bone Benefits Get Big Boosts, and Omega-3s Give Budding Men Better Bones.)
Finally, as she wrote, “… hundreds of studies that have observed a relationship between chronic vitamin D deficiency and age-related muscle loss, cognitive impairment, Alzheimer’s disease, impaired quality of life and decreased ability to carry out activities of daily living.”
In other words, there are many other reasons to take vitamin D supplements as a form of overall health insurance.
The Vitamin D Council advises older people to take 5,000-10,000 IU (125-250 mcg) of supplemental vitamin D daily to gain its wide range of health benefits.
Council for Responsible Nutrition (CRN) response
CRN is the leading trade association for the dietary supplement and functional food industry.
Andrea Wong, Ph.D. of CRN issued a cautionary statement: “All Americans, and older adults specifically, have a basic need for calcium and for vitamin D as both are essential nutrients and are necessary for a host of critical functions in the body, including building strong bones.”
She points out that while the meta-analysis was generally well-designed, the limitations acknowledged by the Chinese researchers themselves preclude generalizations about vitamin D and calcium supplementation for fracture prevention.
She adds: “For older adults, specifically, we know that getting enough nutrients can be problematic, so dietary supplements become even more important."
People find it difficult to get enough vitamin D from diet alone because few foods — with the very notable exception of fatty wild fish like salmon, tuna, and sardines (especially wild salmon) — provide significant amounts of vitamin D.
And, as Dr. Wong said, “Generalized recommendations relying on this study should be mindful that further reductions in calcium and vitamin D consumption may exacerbate these public health concerns.”