But with supplements offering doses as high as 62.5 micrograms available over the counter, there are concerns around the risk of excessive vitamin D levels, which can, in rare cases, cause side effects, including nausea and vomiting. In the long term, some studies suggest too much vitamin D can increase risk of cardiovascular disease, although the research isn’t conclusive.
But others argue that even more vitamin D is needed.
In 2012, chief medical officer Sally Davies wrote a letter to GPs urging them to recommend vitamin D supplements to all at-risk groups, writing that a “significant proportion” of people in the UK probably have inadequate levels of vitamin D. In June 2018, researchers from the University of Birmingham's Institute of Metabolism and Systems Research wrote that the death of a baby from complications of heart failure caused by severe vitamin D deficiency, and the serious health complications of two others, was just the “tip of the iceberg” in vitamin D deficiencies among those at risk.
Suma Uday, co-author of the paper and PhD doctoral researcher at the university, says these deficiencies occur because infant vitamin D supplementation programs are poorly implemented in the UK and not monitored. “In the infants we describe, deficiency occurred because infant vitamin D supplementation was not recommended or monitored. Any infant devoid of vitamin D for prolonged durations can develop low calcium levels, which can result in life threatening complications such as seizures and heart failure,” she says.
With such conflicting results, it’s unsurprising that medical experts themselves are deeply divided over the benefits of widespread supplementation. Some even argue that vested interests are propping up the billion-dollar vitamin industry, with Spector calling vitamin D supplements a “pseudo-vitamin for a pseudo-disease”.
While the debate continues, many experts are looking to Brigham and Women’s Hospital, an affiliate of Harvard Medical School in Boston, whose researchers are carrying out a long-awaited randomised trial, VITAL, to investigate whether supplementation of vitamin D and omega 3 has any effect on cancer, stroke and heart disease in 25,000 adults.
It’s hoped that these results, expected to publish later this year, will bring the debate closer to being resolved. In the meantime, it’s widely agreed that vitamin D supplements, especially over winter, will be a waste of money at worst.
It’s likely you won’t get enough from your diet between now and next spring, but the impact this could have on your health is still up for debate.
All content within this column is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. The BBC is not responsible or liable for any diagnosis made by a user based on the content of this site. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. Always consult your own GP if you're in any way concerned about your health.
Join 900,000+ Future fans by liking us on Facebook, or follow us on Twitter or Instagram.
If you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Culture, Capital, and Travel, delivered to your inbox every Friday.