What is vitamin D and why do we need it to stay healthy?

It’s estimated that around 1 billion people around the world, across all ages and backgrounds, have a vitamin D deficiency. This is usually caused by limited exposure to sunlight, a lack of vitamin D-rich foods, or many other factors including ageing, smoking,  and certain diseases. Many people don’t know that they have low vitamin D levels, because the symptoms associated with this can be very subtle.

However, this vital vitamin (sometimes called the “sunshine” vitamin, because our skin produces it in response to sunlight) has some very important functions. Not only does it contribute to the maintenance of healthy teeth, bones and muscles, but research has suggested that it may even be able to help protect against respiratory tract infections, including Covid-19. The NHS have recently updated their guidance surrounding vitamin and coronavirus with this new information – whilst reminding us that evidence surrounding this claim is still quite limited.

At present, the government recommends that we each consider taking 10mcg of vitamin D a day during the autumn and winter months when sunlight is less available. But, it’s important to keep in mind that while vitamin D deficiency can be harmful, it’s also dangerous to take too much vitamin D – so you should always stick to the national guidelines, unless told otherwise by your GP.

Below, we take a closer look at some of key benefits of vitamin D, and suggest ways to keep your vitamin D levels topped up.

What is vitamin D?

Vitamin D (also known as “calciferol”) is a fat-soluble vitamin that is found in a small number of foods including oily fish and mushrooms. It is also produced by our bodies when ultra violet (UV) rays from the sun hit our skin. People who cannot get enough vitamin D through natural means might be recommended to take supplements by their GP.

The importance of vitamin D when you’re over 50

Stronger bones and muscles

Vitamin D helps the gut to absorb calcium and store it in skeletal tissue. From here, it helps to regulate the production of cells that help to build and maintain bones. Together, vitamin D and calcium can play an essential role in preventing brittle bones and osteoporosis. Scientists have also suggested that it might be able to prevent or delay the onset of rheumatoid arthritis, and improve muscle strength and function, which is important for preventing falls as we get older.

Stronger immune system

Vitamin D helps the body to control and enhance the performance of immune cells – the first line of defence against infection and disease. Deficiency of vitamin D has been widely regarded by experts as something which can contribute to autoimmune disease, highlighting the importance of its role in making sure that we stay fit and healthy.

Some research has suggested that vitamin D might be particularly helpful in protecting against viruses such as the flu, and respiratory tract infections, including those triggered by Covid-19 – although more research is needed to properly validate this claim.

For more tips on how you can boost your immune system, including getting enough sleep and keeping chronic symptoms in check, you might want to have a read of our article; 10 ways to boost your immune system.

Reduced risk of depression

Researchers believe that vitamin D also affects serotonin (often called the “happy” chemical) levels in the brain, having a significant impact on mood. Researchers have so far found a significant connection between depression and vitamin D deficiency, but the inner workings of this are still being explored.

Improved oral health

Vitamin D is one of the biggest contributors to our dental health because it helps the body to take up calcium – which plays a crucial role in the maintenance of healthy teeth and gums. While brushing and flossing are important for keeping your teeth looking clean and white, it’s just as important to look after your gut health and to consider the impact it could be having on your mouth.

Vitamin D and calcium work together to help guard against tooth decay and gum disease, so it’s important to make sure that you’re getting enough of each.

Help with weight loss

Obesity is a known risk factor for vitamin D deficiency, so experts have also looked into how vitamin D might be a helpful aid to weight loss. A 2009 study, published in the British Journal of Nutrition found that a group of overweight or obese women with low calcium levels who took a daily calcium and vitamin D supplement, were more successful at losing weight than those who took a placebo supplement.

Might reduce the risk of cancer

Researchers in Japan looking at whether or not people with higher levels of vitamin D in their bloodstream were less likely to be diagnosed with cancer, found that the risk of cancer was 22% lower. They identified liver cancer as being one of the cancers that might carry a lower risk in people with higher vitamin D levels.

Additional benefits…

Studies have been conducted that suggest that Vitamin D could also:

What is the recommended daily dose of vitamin D?

In order to protect bone and muscle health, the UK government recommends that we each get the equivalent of 10 micrograms (mcgs) or 400 IU (International Units) of vitamin D a day. From late March through to early September, it’s usually possible to get this from sunlight alone. But in Autumn and Winter, the government advises that everyone should consider taking a 10 microgram daily supplement.

They have also recommended that people with dark skin from African, African Caribbean and South Asian countries may also need additional vitamin D, other than that provided by sunlight in the summer. So they might want to consider taking a supplement all year round.

Other people who have a higher risk of vitamin D deficiency including those people whose skin has little or no exposure to the sun, for example, people who cover their skin when they are outside or those who live in care homes, may also find it beneficial to boost vitamin D levels with a supplement.

You can find out more about government guidance on vitamin D intake on the NHS website here.

Is it possible to have vitamin D levels that are too high?

While vitamin D deficiency is fairly common, it’s also possible to end up with vitamin D levels that are too high (this is called vitamin D toxicity or hypervitaminosis D). This is usually a result of taking supplements at a much higher dose than the recommended 10 micrograms a day. Unless there is an underlying health condition, it’s difficult to reach dangerously high vitamin D levels through sunlight and diet alone.

The reason that vitamin D can build up to excessive levels more quickly than some other vitamins is largely because it’s fat soluble. This means that it’s much harder for the body to break down than water-soluble vitamins, like vitamin C and Biotin.

Additionally, vitamin D in our bodies is usually kept in “storage” because it binds to carrier proteins or vitamin D receptors. So when levels are too high, we end up with too much spare vitamin D floating around in the bloodstream. This extra vitamin D can form deposits in arteries and soft tissues, and disrupt and overwhelm biological signalling processes – for example, encouraging the body to absorb more calcium than it needs, which, in extreme cases, can damage the kidneys and nervous system.

Other symptoms of vitamin D toxicity can include high blood pressure, vomiting, poor appetite and bone loss. You can find out more about the symptoms of vitamin D toxicity here. While vitamin D toxicity is quite rare, it’s always a good idea to be aware of the risk and ensure you never take more than the dose recommended in the government guidelines.

4 easy ways to boost your vitamin D intake

1. Spend more time outside, or sitting by a window

The majority of people can get enough vitamin D by exposing their hands, forearms or lower legs to sunlight for short periods of time each day – especially between 11am and 3pm from late late March/early April to the end of September.

It’s difficult to determine exactly how much sunlight a person needs to meet their body’s vitamin D requirements, as this can vary depending on factors such as how much skin someone has exposed, or how much melanin people have in their skin, for example due to their ethnicity. Someone with darker skin may need to spend longer in the sun for their body to be able to synthesize adequate vitamin D, than someone with lighter skin. However, generally speaking, it’s a good idea to make getting outside for some fresh air a daily habit. This can mean different things to different people – you could go for a walk, a bike ride, or simply sit and relax in your garden or a local park.

During the winter, our vitamin D production levels are generally much lower, as there is less sunlight available in the UK. But even on a grey, gloomy day, it’s still possible to get some of the UV rays needed to produce vitamin D – so it’s still worth getting outside during daylight hours.

If for any reason getting outside for some fresh air isn’t an option or, you’d just like to maximise your sunlight exposure as much as possible, then you could also spend some time each day sitting by an open window. It’s important that it’s open, so that the window panes don’t block the UV rays from hitting your skin.

Note: While sunlight exposure is incredibly important for the synthesis of vitamin D, too much time in the sun can also come with significant other health risks including sun burn and an increased risk of skin cancer.As with most things, it’s about finding a healthy balance but you should always cover up your skin or apply sunscreen well before your skin starts to burn.

2. Eat more oily fish, seafood, egg yolks and mushrooms

During the autumn and winter, when the days are shorter and darker, it can help to start looking more closely at how you can introduce more vitamin D-rich foods into your diet.

Oily fish and seafood
Food and drink community forum

Oily fish and seafood are some of the richest natural food sources of vitamin D – with more than half of our recommended daily intake of vitamin D often being present in just 100g of tuna. Other sources of fatty fish and seafood include:

  • Cod liver oil
  • Mackerel
  • Tinned sardines
  • Salmon
  • Shrimp
  • Anchovies
  • Oysters

When cooking fatty fish, it’s best to preserve as many nutrients as possible by steaming or baking it – avoid frying it in oil, as this can reduce the vitamin D content. John West has a great selection of oily fish recipes that you can try out here.

Egg yolks

If you’re partial to a scrambled, fried or poached egg, then you might be pleased to know that egg yolks are packed with vitamin D. Free-range or pasture-raised chickens and/or those who have been fed vitamin D-enriched grain, can have up to four times more vitamin D, meaning that they will usually produce eggs with a higher vitamin D content. Just be careful not to eat too many egg yolks, as they are high in cholesterol. You can try Jamie Oliver’s large range of egg recipes here.


Like us humans, mushrooms can make their own vitamin D when they are exposed to UV rays from the sun – although we make vitamin D3 and they make vitamin D2, which is said to be slightly less effective at raising vitamin D levels. Mushrooms are one of the few plant-based sources of vitamin D, making them an important vegetable to add to your plate – especially for vegetarians.

Wild mushrooms, like shitake mushrooms are generally higher in vitamin D because of their exposure to sunlight, but many commercial varieties found in supermarkets – such as chestnut mushrooms and portobello mushrooms are treated with UV light to naturally enhance their vitamin D levels. To find out how you can incorporate more mushrooms into your diet, you might want to take a look at this list of mushroom recipes from BBC Good Food.

3. Add more vitamin D-fortified foods to your diet

As well as eating food sources where vitamin D is naturally occurring, there are also plenty of foods that have had vitamin D added to them for our benefit. These foods are known as vitamin D-fortified foods. Cows milk, soy milk, fat spreads, orange juice, cheese, yoghurts, tofu and cereals are often fortified with vitamin D, although this will vary depending on the brand. It’s always worth checking the packaging of these foods to get a clearer idea about their vitamin D content.

4. Consider taking a vitamin D supplement if you need a boost

If you’re concerned that you’re not getting enough vitamin D – especially during autumn and winter months – then you could consider taking a 10mcg vitamin supplement each day. If you’re experiencing any of the symptoms mentioned earlier on in this article, then it might also be worth organising a blood test through your GP who can confirm whether you have a vitamin D deficiency, and advise you on the correct dosage to take for your individual circumstances.

When looking at buying vitamin D supplements, you will usually come across two types; vitamin D2 which is produced by plants and vitamin D3 which is produced by animals. Generally speaking, experts believe that vitamin D3 is absorbed better by the body, so if possible, it’s usually best to look for a supplement in this form. Vitamin D3 is usually suitable for vegetarians, although they might not always be suitable for vegans, so it’s always best to check.

Supplements are usually sold as capsules or tablets (or as liquid drops or oral sprays) by a range of different brands. When deciding which vitamin D supplements to buy, always stick to buying high quality products that have been independently tested and sold by reputable brands. The majority of vitamins in the UK are classed as food supplements, which means that they must comply with general food law, such as the Food Safety Act. The Council for Responsible Nutrition UK has issued some helpful advice on how to check whether a food supplement is safe and legal, which you can find here. It’s also important that you buy supplements with a dosage that isn’t higher than the national recommended daily intake of 10mcg, so that you can avoid overdosing. Holland & Barrett offer a range of vitamin D supplements which you can find here*.

A final thought…

Vitamin D is essential for the maintenance of normal calcium and phosphorus levels in the blood, which helps to keep our bones, teeth and muscles healthy – and without it, we might not feel at our best. During the autumn and winter months, it can be helpful to pay particular attention to our vitamin D intake, and take action to raise levels where necessary.

However, as with most things in life, moderation is key. So, if you’re thinking about taking a supplement, then always make sure that the dose complies with government advice (10mcg at most and less if you have a diet rich in vitamin D already). If you feel that you might need more than this due to other factors, then it’s worth having a chat with your GP first, so that they can help guide you towards the correct amount for you.

Are you getting enough vitamin D? Or do you have any additional tips for keeping your vitamin D intake topped up? Join the healthy living conversation on the community or leave a comment below.

Links with an * by them are affiliate links which help Rest Less stay free to use as they can result in a payment or benefit to us. You can read more on how we make money here.


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