Vitamin D and IBD: what parents should know

Vitamin D plays an important role in children's growth, bone health and immune function. For children and teenagers living with Crohn's disease or ulcerative colitis, getting enough vitamin D is particularly important because IBD can increase the risk of vitamin D deficiency.

But why does vitamin D matter for children with IBD? Can low levels affect their condition, and should they take a supplement? Here's what parents need to know.

🦴 Why is vitamin D important?

Vitamin D helps the body absorb calcium, which is essential for building and maintaining strong bones and teeth. It also supports normal muscle function and plays a role in the immune system.

During childhood and adolescence, bones are still developing and growing. Getting enough vitamin D and calcium helps children build healthy bones and achieve their full growth potential.

This is especially important for children with IBD, who may have additional risk factors for poor bone health, including inflammation, nutritional deficiencies and certain medications.

🩺 Why are children with IBD at greater risk of vitamin D deficiency?

Several factors can contribute to low vitamin D levels in children with Crohn's disease or ulcerative colitis.

Reduced absorption

Vitamin D is a fat-soluble vitamin, meaning it is absorbed alongside dietary fat. Inflammation affecting the small intestine, particularly in Crohn's disease, can interfere with nutrient absorption in some children.

Reduced food intake

During a flare, abdominal pain, nausea, diarrhoea or a reduced appetite may make it harder for a child to eat enough foods containing vitamin D.

Less time outdoors

Children who feel unwell or experience fatigue may spend less time outside. Since the body produces vitamin D when skin is exposed to ultraviolet B (UVB) radiation from sunlight, reduced exposure can contribute to low levels.

Inflammation and disease activity

Chronic inflammation may be associated with lower vitamin D levels. Research has found that vitamin D deficiency is common in people with IBD, although it is not always clear whether low levels contribute to disease activity or result from the illness and its effects.

Certain medications

Corticosteroids, such as prednisolone, can affect bone health, particularly when used repeatedly or for extended periods. Children taking these medicines may need closer attention to vitamin D and calcium intake.

🦴 Can low vitamin D affect bone health?

Yes. Vitamin D deficiency can reduce calcium absorption and, when severe or prolonged, contribute to weakened bones.

Children with IBD may already be at increased risk of reduced bone mineral density because of inflammation, poor nutrition, delayed puberty, reduced physical activity or corticosteroid use.

Over time, inadequate vitamin D can contribute to problems with bone mineralisation. In severe cases, deficiency can cause rickets in children, a condition that affects normal bone development.

The good news is that identifying and treating a deficiency can help support healthy bone development.

🧬 Does vitamin D affect IBD inflammation?

Vitamin D has attracted considerable research interest because it plays a role in regulating immune function and maintaining the gut barrier.

Some studies have found that people with IBD who have lower vitamin D levels tend to have more active disease. Other research suggests that correcting a deficiency may be associated with improvements in certain measures of disease activity.

However, these findings do not prove that low vitamin D causes flares or that taking extra vitamin D will bring IBD into remission.

Vitamin D is not a replacement for prescribed IBD medication. It is best viewed as an important part of supporting your child's overall health, especially when a deficiency is present.

Researchers are still investigating whether vitamin D supplementation has additional benefits for controlling inflammation in Crohn's disease and ulcerative colitis.

🧪 Should my child have their vitamin D levels checked?

It's worth discussing vitamin D testing with your child's gastroenterologist, particularly if your child has risk factors for deficiency.

A blood test measuring 25-hydroxyvitamin D, often written as 25(OH)D, is used to assess vitamin D status.

Testing may be particularly relevant if your child:

• Has Crohn's disease affecting the small intestine or has had intestinal surgery.

• Has ongoing diarrhoea, poor food intake or concerns about nutrient absorption.

• Has a history of low vitamin D levels.

• Takes corticosteroids or has other risk factors for poor bone health.

• Has reduced growth, delayed puberty or concerns about bone health.

• Lives in a region or has a lifestyle that limits effective sunlight exposure.

Your child's healthcare team can decide whether testing is needed and how often levels should be monitored. The appropriate testing schedule depends on your child's individual circumstances.

🥚 Which foods contain vitamin D?

Food can contribute to vitamin D intake, although it may be difficult to meet all requirements through diet alone.

Useful sources include:

• Oily fish: Salmon, sardines, trout and mackerel.

• Eggs: The yolk contains vitamin D.

• Fortified foods: Some milk alternatives, dairy products, breakfast cereals and spreads have vitamin D added. Check the nutrition label, as fortification varies between brands and countries.

• UV-exposed mushrooms: Some mushrooms contain vitamin D, particularly when exposed to ultraviolet light.

If your child avoids dairy, fortified plant-based drinks may help provide vitamin D and calcium. Choose products that are suitable for your child's age and dietary needs, and check the labels because not all alternatives are fortified.

For children with restricted diets or ongoing digestive symptoms, a paediatric dietitian can help identify nutritional gaps.

💊 Should children with IBD take a vitamin D supplement?

Some children with IBD need a vitamin D supplement, particularly if blood tests show a deficiency or their healthcare team identifies an increased risk.

The appropriate dose depends on your child's age, current vitamin D level, diet, medical history and whether the supplement is intended to prevent deficiency or treat an existing deficiency.

Your child's gastroenterologist or dietitian can recommend a suitable product and dose. Avoid giving high-dose vitamin D without medical guidance.

Vitamin D is fat-soluble, which means the body can store it. Taking excessive amounts over time can cause vitamin D toxicity and dangerously high calcium levels, potentially damaging the kidneys and other organs.

It's also important to check whether vitamin D is already included in your child's multivitamin or calcium supplement to avoid accidentally doubling up.

🥛 What about calcium?

Vitamin D and calcium work together to support healthy bones. Even if your child has adequate vitamin D levels, they still need enough calcium in their diet.

Children who avoid dairy may obtain calcium from fortified plant-based drinks, calcium-set tofu, selected fish eaten with their edible bones, and other calcium-rich foods.

The amount of calcium a child needs depends on their age. If your child has dietary restrictions, poor appetite or concerns about growth, ask their dietitian to review their calcium intake alongside their vitamin D status.

☀️ Can sunlight provide enough vitamin D?

The body can produce vitamin D when skin is exposed to UVB radiation. However, the amount produced varies depending on factors such as location, season, time of day, skin pigmentation, clothing and time spent outdoors.

There is no single sunlight exposure recommendation that is appropriate for every child worldwide. Sun protection remains important, particularly in regions with high UV levels.

Don't deliberately expose your child to excessive sunlight or allow sunburn in an attempt to increase vitamin D. If sunlight exposure is limited or deficiency is a concern, discuss safer ways to meet their needs with their healthcare team.

✅ What parents can do

You don't need to manage vitamin D alone. A few practical steps can help you support your child's nutritional needs.

• Ask about vitamin D: Discuss whether your child needs a blood test based on their IBD history and risk factors.

• Review their diet: Include vitamin D-containing foods where practical and check whether fortified foods are suitable.

• Check their supplements: Look at labels to see how much vitamin D your child already receives.

• Ask about calcium: Make sure their overall intake supports healthy bone development, especially if they avoid dairy.

• Keep up with follow-up care: Discuss growth, puberty, nutrition and bone health during IBD appointments.

• Seek individual advice: Ask your child's gastroenterologist or dietitian before starting a high-dose supplement.

❤️ The takeaway

Vitamin D is an important part of supporting healthy bones, growth and immune function in children with IBD. Because these children may be more vulnerable to deficiency, it's worth discussing their vitamin D status with their healthcare team.

A balanced diet, appropriate supplementation when needed, and regular nutritional monitoring can help support your child's health as they grow. Vitamin D alone won't treat IBD, but addressing deficiencies is one practical way to look after their wellbeing.