I bet you were told at least once in your childhood to 'eat your greens' - because they would give you strong bones/hair/teeth/muscles/make your hair curl (I had them all!) But no matter how healthy our diet, we're unlikely to get enough vitamin D - so do you need a boost?
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.
Vitamin D and osteoporosis
For the first 20 years I was a doctor, I hardly ever checked anyone's vitamin D levels. We knew low levels were linked to osteoporosis, or thinning of the bones. So we did used to prescribe calcium and vitamin D supplements for people at high risk of breaking a bone. 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. 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.
How thinking about vitamin D has changed
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 was severely deficient. And over that same period, lots more research has emerged about the health benefits of vitamin D.
Are there other benefits of vitamin D?
The obvious health benefit of enough vitamin D is strong bones. Weight bearing exercise is key for preventing thinning bones. Anything except swimming counts - so get out your dancing shoes!
But in recent years, we've discovered that vitamin D regulates at least 1000 genes in the body - affecting blood vessels, immune system, muscle strength and more. Tiredness and muscle pains are the commonest symptoms, But low levels have been linked to an increased risk of depression, heart disease and even multiple sclerosis.
How much is recommended daily?
If you do decide to take a 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.
Public Health England recommends that everyone over one year should take a supplement of 10 micrograms of vitamin D through autumn and winter. 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.
How much is too much?
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 your doctor could put you on a supplement of 20 micrograms a day or 500micrograms once a month. Don't worry - your doctor's not 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.
With thanks to 'My Weekly' magazine where this article was originally published.
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