The latest study on vitamin D cast doubt on supplementation. But here’s what most people aren’t being told about where the research really stands.
During my physical my doctor mentioned a recent study which cast doubt on vitamin D. She wasn’t willing to give up on recommending vitamin D supplements, but wanted to make me aware.
Once again, the public gets a dose of confusion about vitamin D with the latest study headlines. This time, the message is that we may not need D supplements after all; as a registered dietitian, I cringed.
For me, this study did nothing but get me riled up enough to write this post. And here’s why.
Vitamin D: a Look Back
It has been over two decades since researchers began searching for answers about the benefits of vitamin D. That is, following a growing number of observational studies revealing that vitamin D levels are inversely related to several chronic diseases and conditions, beyond its well-accepted role in bone health.
Mostly, results from randomized control studies (RCTs), thought to be the gold standard for establishing cause and effect, have been unclear.
This led to a waning of vitamin D enthusiasm and some health professionals and organizations dismissing screening (blood testing) and recommended supplementation.
But then the pandemic hit.
Vitamin D and The Pandemic
The pandemic brought vitamin D back under the spotlight when a relationship was established between vitamin D levels and the severity of COVID-19.
After all, vitamin D plays an essential role in the immune system, including a known link to respiratory diseases. And so, the RCTs got underway. In typical fashion, the enormous interest in vitamin D waned after not all studies showed benefits.
That brings us to the study making headlines: the Vitamin D and Omega-3 Trial (VITAL). This ongoing trial with 25,871 U.S. men and women is testing if supplementation with 2000 IU vitamin D and 1g omega-3s reduces the risk of chronic disease.
This latest study examined the relationship between vitamin D supplementation and fracture rates in midlife and older adults, showing no significant difference in those taking vitamin D over five years.
The Key Issue with Vitamin D Intervention Studies
A 2018 review led by Mark Bolland from the Department of Medicine, Bone and Joint Research Group, University of Auckland, found that 70% of large, randomized control trials on vitamin D choose individuals who are not deficient.
And the VITAL study was no different. Only 40% of subjects were even tested for vitamin D at the onset, which dwindled to 8% by the end of the study.
“The basic problem with the VITAL study was that it had very few participants with low vitamin D concentrations [25OHD],” said William B. Grant, PhD, Director of the Sunlight, Nutrition, and Health Research Center and author of 304 publications on vitamin D. “For bone health, there seems to be little benefit above 20 ng/mL; the mean 25OHD for those who provided values was 31 ng/mL.”
Not only that, but the control group was allowed over-the-counter supplements, including vitamin D, which made the comparative effectiveness of the active group less. Last, the researchers gave everyone the same vitamin D dose (2000 IU) even when we know people in larger bodies need 2-3 times that amount to raise their blood levels.
In fact, one secondary analysis of the VITAL trial found that people with BMIs under 25 who took vitamin D had a 38% reduced risk of advanced cancers. Could that be because 2000 IU was enough to raise their vitamin D levels but not for those with higher BMIs?
Nutrition RCTs need careful design
These issues have prompted researchers to promote careful design in nutrition studies. In 2014, Robert Heaney put forth guidelines specifically stating that nutrient status must be measured which are shown below.
“The change in nutrient status produced in those enrolled in the trials must be measured and recorded in the report of the trial,” he wrote. “The hypothesis to be tested must be that a change in nutrient status (not just a change in diet) produces the sought-for effect.”
This idea of nutrient measurement that Robert Heaney emphasized eight years ago is something many health professionals and researchers believe is the missing key in the vitamin D clinical research literature.
It begs the question: Why are we focusing more on vitamin D supplementation than the actual vitamin D status achieved in individuals?
It’s Vitamin D status not Supplements that Matter Most
An NIH funded Vitamin D to Type 2 Diabetes (D2d) trial, which gave twice the vitamin D as the VITAL study (4000 IU) demonstrates how results differ when they were based on supplementation alone versus vitamin D status.
Although fewer people in the vitamin D group developed diabetes over two years, the results were not statistically significant. However, in their secondary analysis, researchers found that those who maintained blood levels between 40-50 ng/mL had a 52% reduced risk of developing diabetes, while those with levels greater than 50 ng/mL had 71%, compared to current recommended levels of 20-30 ng/mL.
Endocrinologist Sunil J Wimalawansa provides evidence that vitamin D levels >50 ng/mL are needed for a robust immune system and for reducing COVID-19 complications and mortality.
Research on breast cancer hints at higher levels being beneficial, with one study that pooled two randomized clinical trials and a prospective cohort found women with vitamin D levels >60 ng/ml had 82% reduced risk compared to those with vitamin D levels of <20 ng/mL.
A recent review details how protection may vary per condition with >30 ng/mL found for heart disease and overall mortality, >40 ng/mL for hypertension and preterm delivery, and >50 ng/mL for diabetes and the immune system.
It’s Time to Get Answers!
This latest study on vitamin D doesn’t tell us to forget about supplements. It tells us we need a nutrition study overhaul.
Bolland and colleagues estimated there to be 69% waste in vitamin D studies in bone health alone, with 36% lacking novelty and another 33% adding no new clinical knowledge. We can do better than this.
In 2022, perhaps more than ever, it’s vitally important that we get vitamin D public health recommendations right. We need studies that are better designed and equipped to find answers.
Any researchers up for the challenge?