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Summer in the UK can make vitamin D feel like a non-issue. But for many people, especially in the northern hemisphere, it’s still surprisingly easy to struggle with a vitamin D deficiency in the summer, even when the sun is out. The reason is simple: most of us are not getting enough consistent sun exposure for long enough, at the right time of day, with enough skin showing, to reliably make the vitamin D our bodies need.
Why summer doesn’t always mean enough vitamin D
Vitamin D is made in the skin when UVB light from the sun hits it. In theory, summer should help. In practice, it often doesn’t do enough on its own.
In the UK, we are in a northern latitude, which means sun strength and consistency are limited compared with more equatorial countries. Add in cloud cover, commuting, working indoors and protecting your skin from too much UV, and your “summer vitamin D” can be much lower than you think.
That’s why plenty of people still come up deficient in the warmer months. The weather may feel better, but your vitamin D status doesn’t automatically catch up.
How your skin makes vitamin D
Your skin makes vitamin D when UVB radiation converts a compound in the skin into vitamin D3. But there’s a catch: this only works well when the sun is strong enough, the exposure is long enough, and enough skin is exposed.
That’s why the time of day matters. Around midday, when the sun is higher, UVB is generally stronger and vitamin D synthesis is more efficient. Early morning and late afternoon sun may feel lovely, but it may not give you much vitamin D at all.
And while SPF and long clothing can help to protect the skin from burning, they also reduce the UVB that reaches your skin. So yes, protection matters — but so does understanding that protection and vitamin D production pull in opposite directions.
Why skin tone changes the picture
Vitamin D production is not one-size-fits-all. Melanin, the pigment that gives skin its colour, naturally absorbs UV radiation. That means people with darker skin generally need more sun exposure to make the same amount of vitamin D as people with lighter skin.
This matters in a multicultural country like the UK. A sun routine that works reasonably well for one person may not work at all for another. So when we talk about vitamin D, we should be talking about skin tone, lifestyle and real-world exposure - not just “go outside for a bit.”
This isn’t about suggesting one skin type is better than another. It’s simply about recognising that different bodies need different conditions to make the same nutrient.
Why modern routines get in the way
Most of us are not living outdoors all summer. We’re in offices, schools, cars, indoor gyms, shops and kitchens for most of the day. Even when the sun is shining, our routine keeps us inside for most of the hours when vitamin D could actually be made.
That means a lot of people get the impression they’re “in the sun all summer” when really, they’re getting short bursts here and there. The body usually needs more than that to build and maintain healthy vitamin D levels.
So if you live in the UK and your daily life is mostly indoors, it makes sense to assume you may still need support - even in July.
Cholecalciferol vs calcifediol
This is where the supplement conversation gets more interesting.
Most people are familiar with cholecalciferol (vitamin D3). While it works for many, it requires several conversion steps in the body. If your metabolism is under stress or your genetics aren't optimised for this conversion, you may still show a vitamin D deficiency in the summer despite taking a standard supplement.
Calcifediol is different. It is a more directly usable form that bypasses a major conversion step, raising your levels more efficiently. This makes it a smart option for those who want to ensure they aren't left with a vitamin D deficiency in the summer, as it works alongside your natural sun exposure rather than competing with it.
How to approach vitamin D through the summer
The good news is that this doesn’t have to be all-or-nothing. Your routine can absolutely flex.
If you have a day with a lot of sun, or you’re away on holiday for a week and getting meaningful exposure, you may choose to skip your supplement dose for a few days. That makes sense.
But don’t let those sunny moments fool you into thinking the UK summer alone will reliably maintain optimal levels. For many people, it simply won’t.
A better approach is to think of vitamin D as something you support consistently, then adjust based on actual exposure. That way, your routine matches your life instead of relying on wishful thinking about the weather.
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Key takeaways
You can still be vitamin D deficient in summer, especially in the UK where sun exposure is often inconsistent.
Most of us spend the day indoors, so summer sunshine doesn’t always translate into enough vitamin D production.
Skin colour matters: darker skin needs more sun exposure to make the same amount of vitamin D as lighter skin.
SPF and clothing help protect your skin, but they also reduce vitamin D synthesis from the sun.
Cholecalciferol is the most common supplement form, but calcifediol can be a more efficient option for most people because it bypasses a conversion step.
References
GOV.UK (2014) ‘Vitamin D deficiency: migrant health guide’. Available at: https://www.gov.uk/guidance/vitamin-d-deficiency-migrant-health-guide
Patchworks UK (2024) ‘Vitamin D deficiency in summer, why it happens and how to help’. Available at: https://patchworksuk.com/blog/vitamin-d-deficiency-in-summer-why-it-happens/
Water for Health (2024) ‘Are you getting enough vitamin D even in summer?’ Available at:
https://www.water-for-health.co.uk/blogs/blog/are-you-getting-enough-vitamin-d-even-in-summer
GPnotebook (2017) ‘Sun exposure and vitamin D’. Available at: https://gpnotebook.com/en-IE/pages/dermatology/sun-exposure-and-vitamin-d
Jablonski, N.G. and Chaplin, G. (2018) ‘Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Synthesis’, Dermato-Endocrinology, 10(1). Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC5946242/
Boggia, A. et al. (2023) ‘Benefits and Risks of Sun Exposure to Maintain Adequate Vitamin D Levels’, Nutrients, 15(9). Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC10239563/
Pilz, S. et al. (2019) ‘25-hydroxyvitamin D and Sunscreen Use’, British Journal of Dermatology, 181(5). Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC6899952/
Giusti, A. (2023) ‘Cholecalciferol or calcifediol? A question of narrative!’, Journal of Nutritional Science and Vitaminology. Available at: https://www.vitamind-journal.it
Pérez-Castrillón, J.L. et al. (2021) ‘Calcifediol is superior to cholecalciferol in improving vitamin D status’, Journal of Bone and Mineral Research, 36(10), pp. 1967–1974. Available at:https://academic.oup.com/jbmr/article/36/10/1967/7516555
Tripkovic, L. et al. (2017) ‘Effects of Cholecalciferol vs Calcifediol on Total and Free 25(OH)D’, Endocrine Practice / related review literature. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC5460735/
FAQs
Is it possible to have a vitamin D deficiency in summer?
Yes. In the UK, factors like cloud cover, working indoors, and northern latitudes mean we often don't get enough UVB exposure. Even if you are outside, using SPF or wearing clothing that covers most of your skin can lead to a vitamin D deficiency in summer.
How much sun do I need to avoid a vitamin D deficiency in summer?
It varies by skin tone. Those with lighter skin may only need 15–20 minutes of midday sun, while those with darker skin (which contains more melanin) may need significantly longer to produce the same amount of vitamin D. Without this consistent, direct exposure, a vitamin D deficiency in summer remains a high risk.
Does sunscreen cause vitamin D deficiency?
While sunscreen is vital for preventing skin cancer, SPF 30 can reduce vitamin D production by over 95%. If you always apply high-factor SPF before heading out, your body may struggle to synthesize the "sunshine vitamin," leading to a vitamin D deficiency in summer.
