Low levels of Vitamin D have been associated with a range of diseases. So if we increase our Vitamin D levels will that protect us? How can we do this? Who is most at risk of Vitamin D deficiency? What counts as Vitamin D deficiency? And what are the symptoms?

Having too little Vitamin D has been associated with a range of serious illnesses.

However, an association doesn’t automatically mean that a lack of Vitamin D is causing the illness. It could just be coincidence. Or the illness might be causing the lack of Vitamin D. That’s why there are clinical trials taking place around the world, to try to find out more - like the VITAL study in the US, where initial results suggest that Vitamin D doesn't reduce cancer risks but may reduce cancer deaths.

So what is the current evidence?

Reviews of the research suggest:

How many people have Vitamin D deficiency?

Over half the UK population have insufficient levels of Vitamin D - according to a nationwide survey reported in the BMJ in 2010 – with 16% having severe deficiency during winter and spring.

Who is most at risk of Vitamin D deficiency?

If you’re over 65, pregnant, housebound or with darker skin pigmentation you’re at particular risk.

If you don’t spend much time in the sun or always use sun screen, cosmetics containing sunscreen or enveloping clothing before you go out in the sun you’re also at risk. So too are strict vegetarians, babies who are only breastfed, athletes in northerly latitudes (like the UK) and people who are obese.

As the sun is the main natural source of Vitamin D the risk of deficiency has probably increased as a result of people spending more time living and working indoors and of air pollution. This may also help explain why there has been an increase in Vitamin D deficiency in children.  

What counts as Vitamin D deficiency?

Your doctor may be able to arrange a Vitamin D blood test for you. Most NHS Trusts classify Vitamin D levels as follows: <25 nmoL/L Deficient; 25 – 50 nmpL/L Insufficient; 50 – 75 nmol/L Adequate; >75 nmoL/L Optimal. 

However, higher levels are proposed in the US. Levels above 150 nmoL/L may result in health risks i.e. too much Vitamin D can also be harmful. 

How can we get enough Vitamin D?

The main natural source of Vitamin D is the sun. 10 - 15 minutes exposure per day, between 11.00 am and 3.00 pm, from April to October in the UK, without sunscreen or cosmetics containing sunscreen, should be enough. A bit less if you’re very fair skinned and a bit more if you’re very dark skinned. You don’t need more than this, as too long in the sun, unprotected, can increase the risk of skin cancer.

Oily fish (like salmon, mackerel and sardines) and eggs are another source of Vitamin D, although less significant than summer sunshine. They are particularly important during the winter in countries like the UK, when the sun isn’t strong enough to provide Vitamin D.

Vitamin D supplements are an alternative and you can see the latest guidance on supplements below.

Latest advice from Public Health England

In 2016 Public Health England amended its guidance, in the light of new recommendations from the Scientific Advisory Committee on Nutrition. This advises that adults and children over the age of one should consider taking a daily supplement containing 10mcg of Vitamin D, particularly during autumn and winter - and that people who have a higher risk of Vitamin D deficiency are advised to take a Vitamin D supplement all year round.  

What are the symptoms of Vitamin D deficiency?

Symptoms include fatigue, bone pain, muscle weakness, depression and an above average number of colds (weakened immune system). But often you may have no obvious symptoms.

Is too much Vitamin D bad for us?

You’re unlikely to get too much Vitamin D from sunshine or your diet, as your body has evolved to manage these natural sources.

However, very high doses of Vitamin D supplement increase the risk of nausea, vomiting, weakness and even kidney problems - particularly if you have a liver or kidney condition or take thiazide type diuretics.

So try to get your Vitamin D from sunshine and food. If you take a supplement stick to the recommended dose (i.e. usually 10 micrograms per day).


  • Vitamin D seems to help strengthen our immune system, helping it fight infection.
  • Vitamin D (in combination with calcium) helps prevent rickets and osteomalacia
  • We won’t know whether it can help reduce the risk of other diseases (like some cancers, cardiovascular disease, MS and diabetes) until clinical trials have been completed.
  • Vitamin D from natural sources (sunshine in moderation and food like oily fish) has few health risks.
  • Vitamin D supplements in moderation also have few health risks and are now recommended in winter for everyone in the UK and all year round for at risk groups.

On balance it seems sensible to try to ensure we’re not Vitamin D deficient.

Reviewed March 2020.