Why you might need extra vitamin D even during the summer

A group of people walking down a grassy hill.

When we think about summer, we often think of gloriously sunny days spent outdoors, where our skin can soak up the sunlight and readily produce vitamin D. However, the reality is that even during the summer months certain environmental, metabolic and lifestyle factors can prevent our body’s ability to synthesise and maintain enough vitamin D.

Vitamin D is vital to keep bones strong, mood balanced and our immune system robust; and here I discuss the reasons why you might be someone who needs to continue topping up your vitamin D intake during the summer.

Vitamin D food sources come from eating plenty of oily fish, whole milk, eggs and some outdoor-reared meat. Some shop-bought foods are fortified with vitamin D, however this tends to be vitamin D2 which is the plant-based form that is harder for the human body to absorb. If your sunshine exposure and your consumption of these foods is low, then supplementation can often be very helpful to keep levels maintained, as we only store vitamin D in our system for around 3 months.

If you are concerned that you don’t have adequate vitamin D stores or equally you are worried that you are consuming too much, then it is good to do a finger-prick blood test which can easily be ordered online. Once you have these results you can adjust your dosage of vitamin D supplementation accordingly.

Here are some key reasons why you might need to supplement with additional vitamin D during the summer months.

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Rainy grey days

Even during summer, the UK weather can be very unpredictable. Cloudy, overcast days can limit the amount of UVB rays reaching your skin, thereby reducing the production of vitamin D. If it is raining, we tend to spend even more time inside and cover up with a coat when we are outside. So get outside in the sunshine when you can with as much bare skin as you can bear, and if you have long stretches of dull cloudy days then consider topping up your vitamin D.


If you’re recovering from an illness or surgery during the summer months, you may be spending more time indoors than usual, leading to decreased sunlight exposure and thus less vitamin D synthesis. Try your best to get outside when it is sunny, ideally for 20 minutes showing as much skin as possible which will help you extract the vitamin D from the sunny rays.

Staying indoors to avoid pollen/summer allergies

Hay fever and other summer allergies may force you to choose to stay inside, as sometimes summer allergies can be miserable. When you are spending more time indoors away from pollen you will also be spending time away from the sun and reducing the potential to increase your vitamin D levels. Research has found that people with environmental allergies often have low vitamin D blood levels, and spending more time inside may be one of the reasons why this occurs.

Dark skin

Melanin is the brown pigment that gives dark skin its colour and natural protection from burning in sunnier climates than the UK; but that protection also lowers the skin’s ability to make vitamin D from the same sunlight exposure. Therefore, people with darker skin may need more sun exposure than those with paler skins to generate sufficient vitamin D. Many dark skinned people living in the UK benefit from taking vitamin D as a food supplement all year round.

Sun cream

While sun cream is essential for protecting your skin from harmful UV rays, it can also reduce your skin’s ability to synthesise vitamin D from the sun, as it blocks the UVB rays getting onto your skin and ultimately into the cells of the body. It is thought that a high SPF sun cream can reduce vitamin D synthesis by more than 95%. It is a good habit to apply suncream once you have had 20 minutes of sun exposure but the reality is sometimes this is not possible and its more convenient to apply the suncream before you set off for the day. If that’s the case, you won’t get much vitamin D.

Babies and children covered up

Babies and young children, particularly those with pale or very sun sensitive skin, are often covered up in the summer to protect their delicate skin. This safety measure, while absolutely necessary, can limit their ability to build up their stores of vitamin D for the winter. So, you may want to consider feeding them vitamin D rich foods such as oily fish and eggs as well as supporting their vitamin D levels through supplementation. It is thought that breast milk does not provide adequate levels of vitamin D even if mum is consuming vitamin D rich foods and supplementing.

VDR gene

The vitamin D receptor (VDR) gene plays a critical role in the body’s absorption of vitamin D. There is a vitamin D receptor on every single cell in the body. Think of the VDR genetic SNP as the plug that helps connect the vitamin D in the blood to transport it into the cell to be utilised. Genetic variations in the VDR gene can influence the body’s ability to utilise vitamin D effectively and may make it necessary to increase vitamin D intake all year round. This is a common gene to carry and why many families find they are consistently low in vitamin D and also crave the sun.

Lack of magnesium

Magnesium is a key nutrient that aids in the conversion of vitamin D into its active form in the body. If you have low magnesium levels, your body might struggle to metabolise vitamin D effectively and this can happen just as much in the summer as in the winter. Potential signs of low magnesium can be restless legs, cramps, constipation as well as tics and twitches and poor sleep. Magnesium-rich foods include dark chocolate, leafy greens like salad leaves, cabbage and kale as well as nuts and seeds.

Low cholesterol levels

Cholesterol is also required for the synthesis of vitamin D in the skin. If your total cholesterol blood level is below 4.17, it may affect your body’s ability to produce vitamin D efficiently. So, if you have had a recent blood test and you spot your cholesterol levels are too low, then consume more cholesterol-rich foods such as eggs, butter and offal (liver, kidneys and heart).

Round Up

During the summer there are multiple reasons why you might need to focus on consuming vitamin D rich foods and possibly supplement your vitamin D intake, even if the need is likely to be less than during the winter.

Regardless of the reasons, maintaining adequate vitamin D levels all year round is crucial for your health, and is key for the proper function of your immune system, bone health, and overall mental and physical wellbeing.

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