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How much Vitamin D should you take to boost your immune system?

Vitamin D is needed by your body for a number of reasons. The key functions requiring Vitamin D include the absorption of both calcium and phosphorous, as well as contributing to normal immune function.

Ensuring your body is provided with adequate levels of Vitamin D can aid your body’s immune response and help to improve your body’s ability to fight off illness and disease. In this guide, we’re explaining how Vitamin D works within your body and how you can ensure you’re getting enough to aid your immune system.

In this guide:

Learn more about the types of Vitamin D available

How does vitamin D contribute towards a healthy immune system?

How do you ensure adequate levels of Vitamin D in your body?

Find out more about minimum and maximum Vitamin D dosages

What is Vitamin D?

Vitamin D is a fat-soluble vitamin that plays a role in immune cell function which helps to protect your body from disease.

Vitamin D is made up of a family of nutrients that all share a similar chemical structure. The most common forms of Vitamin D are Vitamin D3 (calcitriol) and D2 (ergocalciferol) and are usually found in your diet. However, there are very few foods that contain Vitamin D naturally.

The role of Vitamin D in your body

Vitamin D is slightly different from other Vitamins because it is a hormone made by your body in a chemical reaction that occurs when your skin is exposed to sunlight. For this reason, it is often referred to as the ‘sunshine vitamin’. However, it is only created by your body if you’re exposed to adequate levels of sunlight.

Vitamin D plays a crucial role in many functions within your body, including immune function. Your immune system is your body’s first line of defence against infection and disease so it’s important to ensure that you’re not experiencing low levels of Vitamin D.

Vitamin D plays a role in the proper functioning of T cells, B cells and dendritic cells which are all key to immune function and protecting your body from infection.

In addition, Vitamin D helps your body to effectively absorb calcium which helps your body to maintain healthy bones.

What are the best sources of Vitamin D?

Many people experience a Vitamin D deficiency because they’re not sure how to make sure they’re getting enough.

There are three key sources of Vitamin D:

  • Exposure to sunlight
  • Food sources
  • Vitamin D supplementation

Let’s take a look at each of these in more detail.

Exposure to sunlight

The most natural way to obtain Vitamin D is to expose your skin to sunshine. Vitamin D is produced endogenously (in the body) when ultraviolet light from the sun triggers Vitamin D synthesis when it hits the skin.

In the UK, between 10 to 20 minutes of sun exposure per day is usually recommended but this is dependent on the time of year and weather conditions. For many people, it’s not possible to get outside for long enough every day so other ways of obtaining Vitamin D may be required. In addition, over-exposure to the sun’s rays carries risks too so this should not be overlooked.

During the winter months, it is less likely that your body’s Vitamin D requirements will be obtained from exposure to sunlight alone. Vitamin D is only stored within your body for two months, so the Vitamin D accumulated during the summer will start to dwindle in the autumn months. Therefore, it may be necessary to find other ways to top up your Vitamin D levels.

Food sources

The most easily absorbed forms of Vitamin D, which are available from both your diet or from supplements, are Vitamin D3 and D2. This is the natural form of Vitamin D that your body makes from sunlight, but it can also be obtained by eating certain foods as part of a healthy diet.

Vitamin D3 is most commonly found in animal-sourced foods such as:

  • Oily fish – tuna, salmon, sardines
  • Liver
  • Eggs
  • Cheese
  • Supplements

On the other hand, Vitamin D2 is found in plant sources and fortified foods including:

  • Mushrooms
  • Fortified foods – cereals, orange juice
  • Supplements

Vitamin D supplements

If you feel you’re not getting enough Vitamin D naturally, you can take a Vitamin D supplement to boost levels within your body. Many people opt to take tablets and capsules but not everyone feels comfortable with taking supplements in this form.

Specially formulated Vitamin D sprays can deliver Vitamin D supplementation through the soft tissue of your mouth, making them a great alternative to tablets and capsules, especially if you struggle or dislike swallowing these.

Depending on how much your Vitamin D levels need to be topped up, sprays are available in three different dosages to make sure you don’t overload your body with too much Vitamin D. Supplements are available in 4000IU (100μg), 3000IU (75μg) or 1000IU (25μg)

For children, even with a healthy diet and exposure to sunlight, it can still be difficult to ensure they’re getting adequate levels of Vitamin D to support their growth and development. It can also be tricky to get young children to swallow tablets too so Infant Oral Sprays and Junior Sprays can be a good option. These sprays contain a lower dosage of Vitamin D than adult versions as children need to maintain a much lower Vitamin D level.



Helping to support bones, teeth and immune system functioning, Vitamin D sprays provide the optimum dosage and enter the bloodstream quickly.

If you’re not sure whether you should be taking Vitamin D supplements or how much your body needs, test kits are available so you can check low levels at home.

How much Vitamin D should be taken to help to boost the immune system?

When taking a Vitamin D supplement, knowing the dosage you should be taking can help you to understand whether you’re taking too much or too little.

Guidelines from Public Health England state that anyone above the age of four should take a minimum of 10 micrograms (400 IUs) daily and children aged between one and four years old should have a 10 microgram daily supplement. In addition, babies under the age of one should have an 8.5 to 10 microgram supplement as a precaution to ensure they get enough Vitamin D.

People who are unable to obtain adequate exposure to sunshine regularly and ethnic minority groups with dark skin are advised to take some form of supplement regularly all year round. You can find out more about at-risk groups in our guide.

Vitamin D requirements can vary widely depending on where you live and your lifestyle. It’s important to remember that 4000 IUs (100 micrograms) is advised as the daily upper limit for Vitamin D intake.

Taking too much Vitamin D can cause a calcium build-up and lead to weak bones, kidneys and heart damage.

Minimum and maximum dosages of Vitamin D

Age Minimum recommended Vitamin D dose Maximum recommended Vitamin D dose
Newborn – 12 months 8.5-10 μg 25 μg
1 – 10 years old 10 μg 50 μg
11-17 years old 10 μg 100 μg
18+ 10 μg 100 μg

What are the symptoms of a Vitamin D deficiency?

If you don’t get enough Vitamin D through diet, supplements or exposure to sunlight, you may find that you start to experience symptoms of Vitamin D deficiency. It’s worth knowing what these are to determine whether you need to increase your intake through your diet or supplements.

Symptoms of low Vitamin D levels include:

  • Muscle weakness
  • Bone pain
  • Fatigue and tiredness
  • Muscle aches or cramps
  • Frequent illness

If you think you may be experiencing a Vitamin D deficiency, you can take a test at home to determine whether you need to boost the levels within your body.

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