What is Vitamin D deficiency and how do I treat it?

November 16, 2022
8 minute read
Cristian Halati

You might have heard of vitamin D being called the “sunshine vitamin”, due to it being produced in the skin with exposure to sunlight.

However, come autumn and winter in the UK - and many other parts of the world - vitamin D starts to crop up more on people's radar when they notice a reduction in daily sunlight levels. Did you know vitamin D is a crucial factor in maintaining good health, and a vitamin D deficiency can lead to a number of serious consequences over time?  

If you’re unsure about your vitamin D levels then read on to find out more about what vitamin D is, what it does, symptoms of vitamin D deficiency, and guidance on supplementing your vitamin D levels.

During these darker winter days, it’s essential to get your daily dose of the sunshine vitamin!

What is vitamin D? 

Vitamin D is a fat-soluble vitamin, meaning it gets absorbed along with dietary fats, and gets stored in fatty tissues and in the liver. It’s generally best known for its role in maintaining bone, teeth and muscle health by assisting in the absorption of calcium, magnesium and phosphate in the body. In addition, vitamin D plays an important role in a range of processes such as a strong immune system, cell growth and regulation of blood pressure.  

Optimal vitamin D levels are crucial for your overall health, and a deficiency can contribute to the development of a range of diseases such as rickets, osteoporosis and multiple sclerosis. Vitamin D deficiency has even been associated with certain types of cancer.  

To date, five forms of vitamin D have been identified. These are called vitamers and two of these are particularly relevant to human health: 

Both vitamers ultimately get converted into the final form of vitamin D in the body. Current scientific research suggests that vitamin D3 is the superior form, as it is more effective in raising the body’s total concentrations.

Where does vitamin D come from?

Around 90% of the vitamin D that is absorbed by the body is through exposure to sunlight, and specifically Ultraviolet B rays (UVB). These types of rays generally reach ground level in the UK at certain times of the day and year - roughly between 11am and 3pm and only from April to September. Out with these times, even if it’s sunny outside, your body won’t be able to produce vitamin D.

Sources of vitamin D

Unlike many other vitamins, only a small amount comes from the foods that we eat - even if we have a healthy diet. Sources of vitamin D include:

Vitamin D deficiency: who is at risk?

Exposure to the right type of sunlight is crucial for obtaining adequate levels of vitamin D and the long cloudy winters in the UK make it very difficult for our bodies to produce enough. Most of the UK population is at risk of becoming deficient at this time of the year.  

As well as reduced sun exposure, several other risk factors for vitamin D deficiency exist, including: 

There are several conditions which may impair intestinal absorption of vitamin D, such as coeliac disease, chronic pancreatitis, Crohn’s disease, and cystic fibrosis. Over time, this reduced intestinal absorption of vitamin D can lead to a deficiency.  

Symptoms of a vitamin D deficiency?

You may notice a range of symptoms which can be a caused by low levels of vitamin D in your body. Some people may not notice any symptoms at all. If you notice any of the following symptoms, then you should visit your GP for a simple blood test to check your vitamin D levels. 

Should I take vitamin D supplements?

The NHS recommends that all adults in the UK take a vitamin D supplement during the autumn and winter seasons, as dietary sources won’t be enough to maintain a good level in your body. The official recommendation for all adults in the UK is to take a daily supplement consisting of 10 micrograms (400 international units) during autumn and winter.  

For people at a higher risk of deficiency, the NHS recommends a daily supplement of 10 micrograms of vitamin D year-round. Find out more about the recommended daily doses.

It’s a good idea to get your vitamin D levels tested by visiting your GP. Depending on your result, your GP may prescribe you a higher daily dose to build your levels back up, and then reduce this to a daily maintenance level dose.  

As a guide, most medical professionals agree on the following Nanomoles Per Litre (nmol/L) scale for measuring vitamin D levels:

It isn’t possible to overdose on vitamin D created from exposure to sunlight, as your body self-regulates production, however taking too many supplements can lead to a more than optimum level in your body. It’s important to check your levels once a year and consult your GP or Pharmacist on the best level of supplementation for you.  

Useful resources

NHS vitamin D guidance

The Association of UK Dieticians


If you have any questions or concerns about your vitamin D levels this winter, get in touch with our friendly pharmacy team who can offer you advice and guidance.

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