Vitamin D supplements do nothing for bone health and the UK government should ditch its advice that everyone should take them throughout the winter months, according to the authors of the biggest ever review of the evidence.
The findings challenge the established view of vitamin D and will dismay the many people who believe a daily dose of it is doing them good. But the large meta-analysis, the authors of which compiled 81 separate studies to come to the most robust possible conclusions, found there was no evidence to justify taking vitamin D supplements for bone health, except for those at high risk of a few rare conditions.
The new meta-analysis is led by the longstanding experts on vitamin D Professors Mark Bolland and Andrew Grey from the University of Auckland in New Zealand and Professor Alison Avenell of Aberdeen University.
Bolland said in the report that things have changed since 2014, when the last major review of the evidence was carried out. In the last four years, “more than 30 randomised controlled trials on vitamin D and bone health have been published, nearly doubling the evidence base available,” he said. “Our meta-analysis finds that vitamin D does not prevent fractures, falls or improve bone mineral density, whether at high or low dose.”
He said the advice given by doctors and government health departments around the world recommending vitamin D and saying it is helpful in osteoporosis or brittle bone disease, which afflicts older people, should now be altered. “Clinical guidelines should be changed to reflect these findings,” he said.
He said further trials looking at the effects of vitamin D on bone health would be pointless. “On the strength of existing evidence, we believe there is little justification for more trials of vitamin D supplements looking at musculo-skeletal outcomes,” he said.
The report says everybody needs vitamin D; the question is whether we should get it from supplements. It is made in the body naturally as a result of exposure to sunlight, which is why people living in northern climates and those who cover up their skin may have lower levels than they should. It is also contained in a small number of foods, such as cod liver oil, offal, egg yolk and oily fish including salmon and mackerel.
The studies that have been done are mostly in older people who could be at risk of osteoporosis (brittle bone disease), but Avenell said there is no evidence of benefit for any adults – apart from those few who are at high risk of osteomalacia, a form of rickets in adults. “I do think they should change the guidance,” she said. “We don’t think that the population needs to take vitamin D supplementation, because trials don’t show it has any benefit in protecting against falls and fractures or all the other things vitamin D is supposed to protect you against.
“There’s no harm in taking low-dose vitamin D supplements as far as we know, but if (the government’s nutrition advisers) really believed it has important effects, surely they should be recommending that there should be fortification of food.”
The report quotes Avenell as saying they were not talking about the effects of supplements in children and young people, because there had not been trials. They were also very clear, she said, that people who were never exposed to the sun because they covered themselves up or were institutionalised were at risk of vitamin D deficiency.
“The context for this analysis lies in the fact that many patients (and doctors) have been persuaded by various studies and social media that vitamin D is a cure-all,” said Dr J Chris Gallagher of the Creighton University Medical Centre in Omaha, US, in a linked comment. “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.
“The authors should be complimented on an important updated analysis on musculo-skeletal health, but already I can hear the fervent supporters – what about the extra-skeletal benefits of vitamin D?”
According to the SACN, there have been suggestions that vitamin D can help with a number of other “extra-skeletal” health issues, including cancer, heart disease, high blood pressure, infectious diseases, neuro-psychological functioning, oral health and age-related macular degeneration, although they did not find convincing evidence for any of these. Gallagher believes studies now taking place will answer those questions.
“Within three years we might have that answer because there are approximately 100,000 participants currently enrolled in randomised, placebo-controlled trials of vitamin D supplementation,” he wrote. “I look forward to those studies giving us the last word on vitamin D.”
Professor Louis Levy, head of nutrition science at Public Health England, maintained in the report that people should continue to take supplements. “With a fifth of people in the UK showing concerning vitamin D levels, government advice is to achieve this from sunshine and a healthy balanced diet during summer and spring,” he said. “During autumn and winter, those not consuming foods naturally containing or fortified with vitamin D should consider a 10-microgram supplement.”
Martin Hewison, professor of molecular endocrinology at the University of Birmingham, agreed, adding that many trials for vitamin D supplementation have shown it is only effective if individuals are vitamin D-deficient to begin with – but that in this research very few participants started off with low levels of vitamin D.
“What the current study illustrates,” he said, “is that more studies are required that target vitamin D supplementation where it is needed – in people with vitamin D deficiency.”
Background: The effects of vitamin D on fractures, falls, and bone mineral density are uncertain, particularly for high vitamin D doses. We aimed to determine the effect of vitamin D supplementation on fractures, falls, and bone density.
Methods: In this systematic review, random-effects meta-analysis, and trial sequential analysis, we used findings from literature searches in previously published meta-analyses. We updated these findings by searching PubMed, Embase, and Cochrane Central on Sept 14, 2017, and Feb 26, 2018, using the search term “vitamin D” and additional keywords, without any language restrictions. We assessed randomised controlled trials of adults (>18 years) that compared vitamin D with untreated controls, placebo, or lower-dose vitamin D supplements. Trials with multiple interventions (eg, co-administered calcium and vitamin D) were eligible if the study groups differed only by use of vitamin D. We excluded trials of hydroxylated vitamin D analogues. Eligible studies included outcome data for total or hip fractures, falls, or bone mineral density measured at the lumbar spine, total hip, femoral neck, total body, or forearm. We extracted data about participant characteristics, study design, interventions, outcomes, funding sources, and conflicts of interest. The co-primary endpoints were participants with at least one fracture, at least one hip fracture, or at least one fall; we compared data for fractures and falls using relative risks with an intention-to-treat analysis using all available data. The secondary endpoints were the percentage change in bone mineral density from baseline at lumbar spine, total hip, femoral neck, total body, and forearm.
Findings: We identified 81 randomised controlled trials (n=53 537 participants) that reported fracture (n=42), falls (n=37), or bone mineral density (n=41). In pooled analyses, vitamin D had no effect on total fracture (36 trials; n=44 790, relative risk 1·00, 95% CI 0·93–1·07), hip fracture (20 trials; n=36 655, 1·11, 0·97–1·26), or falls (37 trials; n=34 144, 0·97, 0·93–1·02). Results were similar in randomised controlled trials of high-dose versus low-dose vitamin D and in subgroup analyses of randomised controlled trials using doses greater than 800 IU per day. In pooled analyses, there were no clinically relevant between-group differences in bone mineral density at any site (range −0·16% to 0·76% over 1–5 years). For total fracture and falls, the effect estimate lay within the futility boundary for relative risks of 15%, 10%, 7·5%, and 5% (total fracture only), suggesting that vitamin D supplementation does not reduce fractures or falls by these amounts. For hip fracture, at a 15% relative risk, the effect estimate lay between the futility boundary and the inferior boundary, meaning there is reliable evidence that vitamin D supplementation does not reduce hip fractures by this amount, but uncertainty remains as to whether it might increase hip fractures. The effect estimate lay within the futility boundary at thresholds of 0·5% for total hip, forearm, and total body bone mineral density, and 1·0% for lumbar spine and femoral neck, providing reliable evidence that vitamin D does not alter these outcomes by these amounts.
Interpretation: Our findings suggest that vitamin D supplementation does not prevent fractures or falls, or have clinically meaningful effects on bone mineral density. There were no differences between the effects of higher and lower doses of vitamin D. There is little justification to use vitamin D supplements to maintain or improve musculoskeletal health. This conclusion should be reflected in clinical guidelines.
Mark J Bolland, Andrew Grey, Alison Avenell