Here's the thing about vitamin D: your child's body is designed to make it from sunlight.
Clever system. One problem: we live in Britain.
Between October and March, the sun isn't strong enough for vitamin D production at this latitudeᵃ. Add in school hours, indoor lives, sensible sun protection, and the fact that "going outside" often means standing in drizzle watching football practice — and it's easy to see why so many UK children run lowᵇ.
This isn't alarming. It's just geography. And once you understand it, it's easier to know what to do about it.
What vitamin D actually does
Vitamin D works across several systems — bones, muscles, and immunity in particular.
Bones and growth Vitamin D helps the body absorb and use calcium properly — which matters a lot when bones are growing fast. Childhood is when the foundations of bone strength are built⁴.
This is especially relevant during those phases where shoes stop fitting overnight and school trousers are suddenly deemed "unacceptable."
Immune function: Vitamin D supports normal immune responses and plays a role in how the body handles everyday bugs¹.
Research suggests children with lower vitamin D status may experience more frequent respiratory infections — though it varies between individualsᶜ. It's not a shield, but it's part of the wider picture.
Muscles: Vitamin D contributes to normal muscle function⁴. For children who are constantly running, climbing, jumping, and mysteriously never sitting still, that matters.
The signs that don't shout
Low vitamin D isn't always obvious. Many children show no clear symptoms at allᵈ. But there are patterns parents sometimes notice — especially over winter.
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The winter slump. Some children seem flatter, more irritable, or less energetic during the darker months. There are lots of possible reasons — but vitamin D is one piece worth consideringᵉ.
- The one who catches everything. If your child seems to pick up every bug going, it may just be normal immune development. But vitamin D plays a role in immune function¹, and low levels have been linked to higher infection rates in some studiesᶜ.
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Achy legs at bedtime. Growing pains are common and usually harmless. But persistent aches or general discomfort can have many causes — and vitamin D supports both muscle function and bone health⁴.
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Tiredness that doesn't add up. Fatigue in children is complicated — sleep, growth, iron, stress, routine all play a part. But unexplained tiredness has been linked to low vitamin D in some research.
Why are some children are more likely to run low
Certain factors make it harder to get enough vitamin D:
- Living in the UK — latitude mattersᵃ
- Limited time outdoors (especially in winter)
- Higher sun protection use — important, but it reduces vitamin D synthesisʰ
- Avoiding or limiting vitamin D–rich foods
- Darker skin tones — melanin slows vitamin D production from sunlightⁱ
- Rapid growth phases, especially in older children and teens
Where vitamin D shows up in food
Not many places, honestly. We evolved to get most of it from sunlight.
Helpful sources include:
- Oily fish — salmon, mackerel, sardines.
- Egg yolks — one of the more accepted optionsʲ
- Fortified foods — some milks and cereals
- UV-exposed mushrooms — yes, reallyᵏ
Even with these, it's difficult to reach recommended intake through food alone — especially in winterˡ. And If your child happily eats mackerel, please share your secrets.
The sunlight window
In the UK, skin can usually make vitamin D from sunlight between April and Septemberᵃ. Short, regular outdoor time helps — but sunburn never does.
Once sunscreen is applied, vitamin D production drops significantlyʰ. That doesn't mean skip sunscreen — just know that food and supplements have a role too.
When food and sunshine aren't enough
Because of geography alone, UK public health guidance recommends vitamin D supplementation for children during autumn and winter — and year-round for some groupsᵐ.
Vitamin D contributes to:
- Normal immune function¹
- Normal growth and development of bones in children⁴
- Normal muscle function⁴
- Maintenance of normal teeth⁶
Vitamin D3 — the form the body makes from sunlight — is generally considered the most effective supplemental formⁿ.
The simple version
Vitamin D is important. UK children are more likely to run low because of where we live. Food helps a bit, sunlight helps when available, and supplements fill the gap when it's not.
Consistency matters more than perfection. And if you're already thinking about this, you're ahead of the game.
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This is general information, not medical advice. If you have questions about your child's health, your GP or a registered healthcare professional is always the right place to start.
Supporting references
ᵃ Webb AR et al. J Clin Endocrinol Metab (1988). ᵇ Cashman KD et al. Am J Clin Nutr (2016). ᶜ Martineau AR et al. BMJ (2017). ᵈ Holick MF. Rev Endocr Metab Disord (2017). ᵉ Cheung AH et al. Nutrients (2018). ᶠ Johnson K & Sattari M. SpringerPlus (2015). ᵍ Sajid M & Mughal MZ. Paediatrics & Child Health (2021). ʰ Matsuoka LY et al. J Clin Endocrinol Metab (1987). ⁱ Farrar MD et al. J Invest Dermatol (2011). ʲ PHE. McCance and Widdowson's Composition of Foods (2019). ᵏ Cardwell G et al. Nutrients (2018). ˡ NHS. Vitamin D (2020). ᵐ SACN. Vitamin D and Health (2016). ⁿ Tripkovic L et al. Am J Clin Nutr (2012).
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