Your child gets vitamin D from food, supplements and the sun – the primary source being exposure to sunlight. (The next email in this series explains what safe sunlight exposure for your child is, so look out for that!)
A study in Northern Ireland found that half of schoolchildren were deficient in vitamin D, with a level below 50nmol/l. Another found that low vitamin D levels in childhood predict behaviour problems in adolescence.1 Low vitamin D status in both the mother and newborn baby also considerably increase the likelihood of the child developing neurodivergence.2
How do you know your child is getting enough? Ultimately, only a pin prick blood test confirms this – at Food For The Brain, we offer at home finger prick blood tests https://foodforthebrain.org/tests/.
We recommend an optimal level for both children and adults is above 75 nmol/l or 30ng/ml in the US).
In truth the amount your child ‘needs’ depends entirely on what gets your child’s blood level up to an optimal level. The table below shows you what you are aiming to achieve:
| Low | Below 50 nmol/l | Below 20 ng/ml |
| Medium | 50–74 nmol/l | 20 to 29.6 ng/ml |
| Optimal | 75–150 nmol/l | 30–60 ng/ml |
| UK Measure (nmol/l) | US Measure (ng/ml) |
Why does it matter:
✔ The biggest source of vitamin D is from sunlight exposure. There’s a cool free app at https://dminder.ontometrics.com/ which works out how much vitamin D you’re making depending on where you live, the time of year and a few facts about yourself. But, as soon as your shadow is longer than your body, the angle of the sun is no longer enough to make vitamin D.
✔ This means that, even in the summer, your child can only make vitamin D towards the middle of the day. But you can make all your vitamin D in 30 minutes. For children, to protect them from the harmful effects of the sun, the best rule is to have more skin exposed but wear a hat to protect the face. For example, when it’s warm enough, wearing shorts and a t-shirt is ideal.
✔ In terms of food – seafood, especially oily fish, provides the most dietary vitamin D, and is an important source but, in winter, this plus getting outdoors, is not enough. A portion of salmon or mackerel gives about 400iu (10mcg) compared to white fish, which is about 200iu (5mcg). A cup of milk gives 3mcg and an egg (40iu)1mcg.
✔ A child, eating fish and eggs might achieve 500iu at most. Without sun, a child needs an intake of about 1,000iu (25mcg) to achieve that optimal blood level. So that means supplementing.
✔ Up to 2,000ius a day is considered safe for infants and up to 4,000ius for children. Teenagers have effectively the same needs as adults. Many people take 3,000ius a day in the winter to keep their vitamin D blood level topped up.
✔ All children need to supplement in the winter unless living closer to the equator. The https://dminder.ontometrics.com/ app will work this out for you and tell you how much you’re making. It is not only important for their bone development but also their immunity, as well as mental health and mood.
What You Need to Know:
In Winter (October–March in the UK):
• Children usually need to supplement 2,000 IU of vitamin D per day (adults need around 3,000 IU), assuming they’re getting about 500 IU from food.
• Why more in winter? Because we don’t get enough sun exposure to make it naturally.
In Summer (April–September):
• When the sun is strong enough (your child’s shadow is shorter than their body at midday), you can reduce supplements to 400–1,000 IU per day (10–25mcg).
• This helps top up levels if your child isn’t getting much sunshine or wears a lot of sunscreen.
Not all children make vitamin D equally
• Children with darker skin naturally produce up to 6x less vitamin D from sunlight due to melanin (skin pigment).
• Children who are overweight may also need more—because vitamin D gets stored in fat cells and doesn’t circulate as well.
A reminder – what is the Vitamin D goal?
• Good blood level: 75 nmol/L
• Ideal range: 90–150 nmol/L (that’s 40–60 ng/mL on some lab reports)
How to supplement
• Many children’s multivitamins contain around 200 IU, which is too low on its own in winter.
• Look for vitamin D drops or sprays—easy to use and widely available.
• For best results, vitamin D works even better when combined with vitamin K2 and magnesium, so check the multivitamin label.
• Vitamin D3 is more effective than D2 and can come from:
– Animal sources (like lanolin from sheep’s wool) – Vegan-friendly sources (like lichen)
• Mushroom-based D2 is available too, but it’s less effective at raising levels.
Vitamin D and your child’s brain & immunity
• Supplementing 800 IU daily for a year has been shown to support cognitive function and reduce markers linked to dementia.
• Low vitamin D is linked with a higher risk of:
– Repeated infections
– Poor immunity – Chronic diseases later in life (eg. diabetes, heart disease, dementia)
If your child keeps picking up infections do check their vitamin D level with a simple blood test.
UK vs Ireland Recommendations
• UK recommends: 10mcg (400 IU) daily in winter for everyone over 1 year old
• Ireland recommends: 25mcg (1,000 IU) all year round for immune support
• The latest research (and the Endocrinology Society) supports the higher intake levels recommended above, especially in winter.
How to Implement Change
Today’s Challenge: Check if your child is getting enough safe sun or an appropriate supplement. If not, consider adding a vitamin D3 supplement to their daily routine—especially during autumn and winter.
💬 Encouragement for Parents: This small nutrient packs a big punch. By ensuring your child has enough vitamin D, you’re helping build resilience in both body and brain. Keep up the brilliant work!
📌 Next email: Safe sun guidance for your child
Wishing you and your child the best of health and happiness,
The COGNITION for Smart Kids & Teens Team
References: 1. 147. S Robinson et al., Vitamin D Deficiency in Middle Childhood Is Related to Behavior Problems in Adolescence, The Journal of Nutrition, Volume 150, Issue 1, 2020, pp.140–148, ISSN 0022-3166, https://doi.org/10.1093/jn/nxz185.; 2. Wang Z et al.,The Association between Vitamin D Status and Autism Spectrum Disorder (ASD): A Systematic Review and Meta-Analysis. Nutrients. 2020 Dec 29;13(1):86. doi: 10.3390/nu13010086.