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How to Optimise Your Vitamin D Levels

An easy-to-digest overview of what vitamin D is and why it is important for health

  1. Dietary sources of vitamin D

  2. Functions of vitamin D

  3. Vitamin D supplements

  4. Improving vitamin D absorption

  5. Spending time in the sun

Vitamin D is an essential vitamin and hormone, with key roles in bone health, immune function and nutrient metabolism. Lack of this vitamin can lead to a number of symptoms including:

  • Fatigue

  • Joint aches

  • Mood changes

  • Muscle cramps

  • Bone loss or weakening

Vitamin D deficiency and insufficiency are common in the UK.

However, these symptoms are not always obvious or may appear unrelated. This means optimising your vitamin D status through diet, lifestyle behaviours and supplementation is crucial for prevention of deficiency.

Spending time in the sun

Have you ever heard of vitamin D being referred to as the sunshine vitamin D? Let me explain why...

How much sun exposure do we need?

Vitamin D can be synthesised via the UVB sun rays hitting our skin. This process begins in the skin the travels through the circulation to the liver and kidneys to produce the active form of vitamin D which our bodies utilise. Daily sun exposure during the summer helps us stock up our vitamin D stores which we need as reserves for the rest of the year.

However, be mindful to balance this with being sun safe! A good plan is to avoid long periods of sun exposure from 11am to 3pm (when the sun is most intense) without sun protection, and instead having 10 - 30 minutes of sun exposure and then applying your usual SPF after this.

Time required outside depends on a number of factors including:

  • Skin colour

Folks with darker (melanin-rich) skin tones are more protected from the sun's rays and therefore need to spend longer in the sun to absorb enough vitamin D.

  • Age

The efficiency with which our skin can synthesise vitamin D reduces as we age. This is why it is recommended that adults over 65 years take a vitamin D supplement year round.

  • Clothing

It is common for some people to wear clothing which covers up the majority of their skin for religious or cultural reasons, but also just wearing long sleeves and full length trousers reduces the amount of skin exposed to the sun and therefore reduces vitamin D production.

  • Weather, cloud coverage

Completely logical that if heavy clouds are blocking the sun, the UVB rays will be less intense and less vitamin D will be produced in our skin.

  • Time of day

The peak hours when the sun's rays are most intense falls between 11am and 3pm. During this time less sun exposure will be required to reach the same level of vitamin D production in the skin.

  • Latitude

For those living above 37 degrees north, the sun will not be intense enough to produce any vitamin D in the skin during winter months. This makes location a risk factor in vitamin D deficiency. For reference, Newcastle Upon Tyne is at 55 degrees north!

Vitamin D supplements

From September to March the UK sun does not provide strong enough UVB rays to enable any vitamin D production in our skin. For this reason, a 10ug (microgram) daily supplement of vitamin D3 is recommended for the UK population by the NHS. This applies to everyone including pregnant and breastfeeding women.

Supplementation can be continued during summer months if you're at risk of deficiency or don't get enough sun exposure e.g. those who dress fully covered for religious reasons or with darker skin.

If you're not a fan of taking tablets, try a Vitamin D Spray.

I've recently become an affiliate partner for Rhitrition+, a registered nutritionist founded brand of trusted, traceable supplements. I'd love to share my discount code with you for 10% off your order - use code EMILYGREEN10 at

Dietary Sources of Vitamin D

Oily Fish

Salmon, herring, sardines & mackerel all contain vitamin D3 along with health omega-3 fats. Wild fish tend to have higher levels than farmed fish.


Egg yolks in particular are rich in vitamin D and fats which help the absorption, so choose the whole egg not just the white!


Mushrooms are a source of vitamin D2, interestingly, when they are grown in sunshine. Read on to see how this is similar to how we absorb vitamin D from the sun...

Fortified Products

Some cereals and milk alternatives have vitamin D added in at the point of manufacturing. Check the label to make sure D3 (cholecalciferol) and not D2 (ergocalciferol) is added.

Improving vitamin D absorption

Even if your diet is rich in vitamin D containing foods like oily fish, sun-soaked mushrooms and fortified milks, there are still ways you can optimise vitamin D absorption from these foods.

Along with vitamins A, E and K, vitamin D is fat soluble. This means it does not dissolve in water and requires dietary fat to enable its absorption in our digestive tract. Healthy sources of fat include eggs (especially the yolk), avocado, full-fat dairy, extra virgin olive oil, nuts and seeds.

It can be beneficial to take your vitamin D supplement with a meal so that vitamin D and the absorption-assisting fats are digested together.

Functions of Vitamin D

Vitamin D helps with:

🥛 Absorbing calcium from the diet

Vitamin D and calcium are nutrient besties. Together they allow optimal absorption of calcium from the diet which is an essential nutrient throughout the body.

🦴 Keeping bones strong

One of the key functions of calcium is building and maintaining healthy bones. Without vitamin D to help absorb it, even high intakes of calcium won't be able to fulfil their purpose.

📊 Maintaining normal blood levels of other nutrients such as calcium + phosphorus

Vitamin D helps keep concentrations of calcium and phosphorus at an optimal level by signalling mobilisation of calcium to and from bone matter or affecting how much is absorbed by the kidneys.

🦠 Supporting immune function

We often think of vitamin C as being the key nutrient for the immune system but in fact vitamin D aids crucially with both our innate and adaptive immune responses. In vitamin D deficiency we see this illustrated through increased autoimmunity and higher susceptibility to infections.

Normally, I like to take the food first approach, but we make an exception with vitamin D. Even with a diet rich in vitamin D containing foods it's tricky to get enough of the nutrient in gloomy winter months. So, it is recommended everyone takes a 10ug (microgram) supplement of D3 during winter in the UK as the sun is no help to us! ☁️


Thank you for reading this blog post on vitamin D.

If you enjoyed this and my affiliate discount code for Rhitrition+, come & join the community on Instagram too @nutritionupontyne



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