Vitamin D supplements do nothing for bone health and the government should ditch its advice that everyone should take them throughout the winter months, according to the authors of the biggest review of the evidence ever carried out. 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 Department of Health currently says everyone should consider taking a vitamin D supplement for their bone health in the winter months, between October and March, if they cannot get enough by exposure to sunlight. That includes all infants and children from six months to five years. It is based on findings from the government’s scientific advisory committee on nutrition (SACN) in July 2016, which did not conclude there were other proven health benefits. The new meta-analysis is published in the Lancet Diabetes and Endocrinology journal and led by the longstanding experts on vitamin D Profs Mark Bolland and Andrew Grey from the University of Auckland in New Zealand and Prof Alison Avenell of Aberdeen University.
Bolland said 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 a 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 musculoskeletal outcomes,” he said.
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 a fortification of food.”
They were not talking about the effects of supplements in children and young people, she said 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 J Chris Gallagher of the Creighton University Medical Center in Omaha, USA, in a linked comment in the journal. “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 of musculoskeletal 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, neuropsychological 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.” Prof Louis Levy, head of nutrition science at Public Health England, maintained 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.”
Credit: Sarah Boseley for The Guardian, 4 October 2018.
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