Should you take a vitamin D supplement every day?

Why do we need vitamin D?

Vitamin D is often called the 'sunshine vitamin'. Sunshine really does make us feel good. Seasonal affective disorder (SAD) is a form of depression caused by lack of sunshine. But it does more - about 90% of our body's vitamin D is made in our skin from sunshine falling on it. That's all very well if you live in the Mediterranean, but in gloomy old Britain, the sun isn't strong enough between October and April to give us any vitamin D.

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Is vitamin D deficiency common?

For the first 20 years I was a doctor, I hardly ever checked anyone's vitamin D levels. We knew people with very low levels were at higher risk of 'thinning' of the bones (osteoporosis). So we did used to prescribe calcium and vitamin D supplements for people at high risk of breaking a bone.

Occasionally we'd check someone's blood levels of vitamin D and discover they were very low - so we'd give them a single injection of very high-dose vitamin D. But that was about it.

In the last decade, there has been a complete revolution among doctors in our attitudes to vitamin D. Once we started measuring it, I certainly discovered at least half my patients were short of vitamin D and one in six patients were severely deficient. So we started recommending vitamin D supplements routinely for anyone at risk of developing osteoporosis as well as other conditions (more of those later).

But on 5th October 2018 a new study on vitamin D and osteoporosis was published which is likely to change our thinking again.

Do vitamin D supplements work?

In the past, scientists have become very excited about other 'antioxidant' vitamins, particularly vitamins A, C and E and their role in preventing heart disease. The thinking went something like this: people who eat lots of fruit and veg are less likely to have heart attacks; fruit and veg are high in antioxidant vitamins; antioxidants are a good thing because they mop up 'free radicals' which can damage DNA; so if people don't get their required amount of vitamins through fruit and veg, giving them in supplement form of vitamin will be just as good. In fact, when the studies were done, topping up with supplements didn't cut heart disease risk at all.

The new study shows a similar result for vitamin D, at least as far as fractures, falls and bone density are concerned. There is no evidence that taking vitamin D supplements reduces the risk of fractures or falls, or improves bone density. So doctors need to question whether they should be prescribing to people at risk of osteoporosis, and we all have to go back to the drawing board to protect ourselves.

Which foods contain calcium?

For strong bones, calcium is also important. Dairy products, seeds, pulses, tofu, tinned fish with bones and some green leafy vegetables are all good sources. Interestingly, calcium supplements don't appear to help much, and recent research suggests they may actually increase the risk of heart attack, so doctors are much more wary about prescribing these too.

But there is one sure-fire way to keep your bones strong - and it's never too early to start. weight loss and weight-bearing exercise are key to preventing thinning bones. Anything except swimming counts - so get out your dancing shoes!

When to take vitamin D

It's important to put this new study into context. It didn't look at babies and children under 5, so does nothing to undermine the current Public Health England guidance that they, along with pregnant women, should take a daily vitamin D supplement. People who are at risk of vitamin D deficiency because they cover up for religious reasons or don't get outside at all should also continue to take supplementation.

In addition, this study was only looking at the impact of vitamin D on bone health. In recent years, we've discovered that vitamin D regulates at least 1,000 genes in the body - affecting blood vessels, immune system, muscle strength and more. Tiredness and muscle pains are the most common symptoms, but low levels have been linked to an increased risk of depression, heart disease and even multiple sclerosis.

As yet, there haven't been any large scale studies looking at whether taking a vitamin D supplement, if you're at risk of deficiency, protects against any of these. But vitamin D at the recommended levels doesn't appear to have any adverse side effects: so if Vitamin D supplements does offer any protection at all, the risk: benefit ratio is likely to come down in favour of taking them.

How much vitamin D should you take daily?

If you do decide to take a vitamin D supplement, it can get a bit confusing. Vitamin D doses can either be measured in international units (IU) or in micrograms (mcg) and levels are very different. It's easiest to stick to one - I'd recommend you look out for the number of micrograms. For reference, 10 mcg is equivalent to 400 IU.

Public Health England (PHE) recommends that everyone over one year should take a supplement of 10 micrograms of vitamin D from around the end of September to early April. If you don't get outside much, or if you cover up for religious reasons or have darker skin, you should take it all year round. It's too early to tell if this new research will affect their recommendations.

Dr Louis Levy, Head of Nutrition Science at PHE, says: "A healthy, balanced diet and short bursts of sunshine will mean most people get all the vitamin D they need in spring and summer. However, everyone will need to consider taking a supplement in the autumn and winter if they don't eat enough foods that naturally contain vitamin D or are fortified with it. And those who don't get out in the sun or always cover their skin when they do, should take a vitamin D supplement throughout the year."

Can you take too much vitamin D?

Many people don't realise that you can have too much of a good thing. In very high doses, many minerals (like iron) and vitamins can harm your body. Current guidelines say adults shouldn't take more than the equivalent of 100 micrograms a day. But vitamin D is a 'fat-soluble' vitamin, so your body can store it for months and you don't need it every day. That means you could equally safely take a vitamin D supplement of 20 micrograms a day or 500 micrograms once a month. Don't worry - your doctor or pharmacist aren't trying to poison you! You can divide the monthly dose by 30 to give you the daily equivalent, which is what counts.

Of course, speaking of too much of a good thing, too much sunshine can be disastrous for your health. Any redness or even tanning of your skin is a sign that your skin has been damaged. In spring and summer, you can get your vitamin D from 15 to 20 minutes a day with arms and face uncovered in full sun. But don't get burnt - this raises the risk of all kinds of skin cancer, but particularly of deadly melanoma.