Vitamin D supplements do not prevent fractures, falls or improve bone mineral density in adults, according to a major new study published in the prestigious journal, The Lancet Diabetes & Endocrinology.
The study’s results run contrary to many sets of guidelines around the world, including Australia, that recommend vitamin D supplementation.
They also challenge the highly lucrative vitamin D testing industry.
Funded by the Health Research Council of New Zealand, the study was conducted at the Universities of Auckland and Aberdeen in Scotland.
Its authors conclude there is little justification to use vitamin D supplements to maintain or improve musculoskeletal health, except in people with rare medical conditions that put them at high risk.
These rare conditions are rickets and osteomalacia (bone softening), which can occur due to vitamin D deficiency after a prolonged lack of exposure to sunshine.
Vitamin D is known as the sunshine vitamin because the body produces it when bare skin is exposed to sunlight. Small amounts of this vitamin can also be obtained from food.
The latest study involved an analysis of the combined results of 81 randomised controlled trials of vitamin D and bone health.
“Despite this new evidence, there is still an awful lot of positive enthusiasm about supplementation and I’m not sure our large study will be enough to switch it off,” says lead author Mark Bolland, associate professor of medicine at Auckland University.
An unscientific jump
He says the vitamin D myth began in the early ’90s when a study on the frail and elderly, in rest homes and nursing homes and not getting any sun exposure at all, were given supplements during an 18-month trial.
The results suggested vitamin D prevented a third of hip fractures among them. As the results were compelling and the trial was well conducted, people assumed it would apply to other groups. This was an unscientific jump.
The extrapolation gained a momentum of its own, the industry grew and guidelines shot way ahead of the evidence.
In the process, vitamin D, became the rock star of the vitamin industry, burning brightest about five years ago, with Medicare paying around $150 million on blood tests for it and with many more tests being performed in the private sector – in the name of good bone health.
As large-scale reviews began reporting no effect of vitamin D supplementation on bone mineral density, falls or fractures, it began to lose some lustre.
But, as this was happening, so benefits beyond bone health were being explored and a new fad, claiming vitamin D’s effectiveness in everything from cancer to cardiovascular disease, took hold.
Once again, Professor Bolland says, this was driven by enthusiasm not evidence.
On bone health, he believes clinical guidelines that continue to recommend vitamin D supplementation should be changed to reflect the best available evidence.
“Since the last major review of evidence in 2014, more than 30 randomised controlled trials on vitamin D and bone health have been published, nearly doubling the evidence base available.”
Driven by enthusiasm not evidence
He says there is little justification for more trials of vitamin D supplements looking at bone health.
“The message of our study is that if you are fit and healthy, you don’t need to take vitamin D supplements and this applies to most people, even those with medical conditions.
“If you are fair skinned and have some form of tan towards end of summer, I would say your vitamin D levels are going to be fine throughout the whole year and I wouldn’t worry or measure them.
“Vitamin D is difficult to measure, and a sample measured in one laboratory will often be markedly different if measured in another laboratory. So, just because you have a low level, it doesn’t mean your vitamin level is actually low.
“It might depend on what assay the laboratory uses to measure vitamin D.”
The Osteoporosis Australia website states that over 30 per cent of Australian adults have a mild, moderate or even severe deficiency.
It says only people at risk of vitamin D deficiency may need vitamin D levels checked, as determined by a doctor.
Overall, it recommends most people should have a vitamin D level of at least 50 nmol/L at the end of winter, which means they may have levels 60 to 70 during summer.
No reliable effect
Professor Bolland says most of the trials included in his study were in people who had levels below 50. Raising them above 50 had no reliable effect on bone health.
“The authors should be complimented on an important updated analysis on musculoskeletal health,” says Professor Chris Gallagher, a distinguished researcher into vitamin D.
In a linked comment in the journal, he writes that “many patients and doctors have been persuaded by various studies and social media that vitamin D is a cure-all.
“This thinking is reminiscent of the fervour that supported the widespread use of vitamin A, vitamin C, and vitamin E years ago, and all of those vitamin trials later proved to be clinically negative.”
But Gallagher, Professor of Medicine and Director of the Bone Metabolism Unit at Creighton University, Nebraska, says there are still unanswered questions as to whether vitamin D might benefit conditions unrelated to bone health.