Should we all be taking vitamin D supplements in winter?

Manuel Breva Colmeiro / Getty Images / WIRED

For many, the winter months mean leaving for work in the dark, coming home in the dark and spending all day in an office lit by fluorescent lights. Without the blue skies of summer, your skin isn’t soaking up much sunlight for your body to create vitamin D.

Between the months of January and March, more than a quarter of adults (29 per cent) in the UK are vitamin D deficient. To tackle this, Public Health England has suggested that from October to March everyone should consider taking vitamin D supplements. It seems like an easy fix: not enough sunlight? Just take a pill instead.

Earlier this year, research firm Mintel reported that vitamin D overtook vitamin C as the UK’s most used supplement. But for those who aren’t lacking the vitamin, supplements could prove to be completely unnecessary. So is it really worth everyone taking on extra vitamin D?

First, the physiology. Vitamin D helps the body to absorb calcium – a key ingredient in keeping bones strong. Severe deficiency can lead to rickets in children and osteomalacia in adults where the bones are softened.

“Adults, especially in wintertime, often experience aches and pains in their bones and muscles,” says Michael Holick, a professor of medicine at Boston University. “It turns out to be vitamin D deficiency osteomalacia that causes aches and pains, and taking vitamin D can help prevent that from happening.”

In the world of medicine, vitamin D has taken on almost mythic properties. Recently it was found that every cell in the body has a vitamin D receptor, and so the benefits of maintaining a healthy level could be more than we currently realise. This is why studies into the impact of vitamin D are experiencing a boom at the moment, with some claiming that deficiency can increase the risk of multiple sclerosis, diabetes or even cancer.

The UK government has been advised by the Scientific Advisory Committee on Nutrition (SACN) that everyone should try to get 10 micrograms per day of vitamin D. SACN found that there was an increased risk of poor musculoskeletal health when the concentration of vitamin D in the blood dipped below 25 nmol/L. It concluded that the best way to prevent it from falling below this level was to suggest a supplement.

It’s a better-to-be-safe-than-sorry approach as in the UK we don’t get our milk fortified with vitamin D, unlike other countries such as the US. You can get vitamin D from dietary sources like fatty fish and leafy greens, but not enough to provide what you need in the winter. Supplements seem like the ideal solution, though many people end up taking it without knowing what it’s actually doing for them.

There is the risk of taking too much. Vitamin D isn’t a nutrient that will simply flush away if your body gets too much of it. As it helps with the absorption of calcium, too much vitamin D may mean that calcium ends up in other parts of the body.

“If you are also taking in a huge amount of calcium and you already have a high level of vitamin D, you might get high calcium,” says Edward Zawada, a researcher and medical doctor from the University of South Dakota. “That is not good for your body. It starts depositing not only in bone like it’s supposed to, but it starts depositing in other tissues too.”

The Vitamin D Council suggest that this problem, called hypercalcemia, can be caused by taking over 250mg per day over a period of months. This means that while supplements shouldn’t be taken in large quantities or when you don’t need them, like in summer, taking a 10mg tablet every day won’t cause too much harm. “As long as you’re not simultaneously downing a lot of calcium in the way of supplements are our dairy products then it’s probably pretty safe,” Zawada says.

If you’re one of the 71 per cent of people who aren’t deficient in vitamin D, taking supplements over winter may not harm your body, but it may harm your wallet. The cost involved means that not everyone will be able to afford supplements. Though the government currently has its Healthy Start scheme to give vitamins to parents and pregnant women from low income backgrounds, this doesn’t cover everyone.

Mark Bolland, associate professor of medicine at the University of Auckland worries that the government strategy of suggesting supplements for everyone will mean people in lower socio-economic groups will get left behind.

“For the last few years, the UK population has been spending more than £100 million every year on vitamin D supplements,” Bolland claims. “However, there is little evidence that rates of rickets or osteomalacia are declining,” he says, adding that people on lower incomes “would probably benefit most from supplements” and that such policies risked “entrenching health inequality”.

So should you consider taking a vitamin D supplement? If you’re sensible and only consuming 10mg per day with not too much calcium, you should be okay. While we still don’t know all of the health benefits, between October and March you have little chance of being able to get the vitamin D from your diet or the sun alone, so it’s worth thinking about it. Although, it’s always worth considering consulting your doctor to find the best plan for you.

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