Understanding vitamin D

Vitamin D is a fat-soluble vitamin that our bodies can produce when our skin is exposed to sunlight (specifically UV rays). It’s also found in a few foods, such as cod liver oil, salmon, eggs, and in fortified foods like cereals, milk, and dairy products. However, since only small amounts are present in food, vitamin D3/cholecalciferol supplements (a highly absorbable form of vitamin D) are often the best way to ensure your child is getting enough vitamin D. 

Vitamin D is essential for many body functions. Most importantly, it supports bone growth and development, helps muscles function properly, strengthens the immune system, and plays a role in calcium absorption.

How much vitamin D do children need?

The Recommended Dietary Allowance (RDA) in international units (IU) for vitamin D is:

• Infants (0 to 12 months): 400 IU/day

• Children (1 to 13 years): 600 IU/day

What is vitamin D deficiency?

Vitamin D deficiency occurs when there isn't enough vitamin D in the body. Clinically, this is defined as a blood serum level below 20 ng/mL in children. Levels between 20 and 29 ng/mL are considered "insufficient."

A lack of vitamin D can affect bone development and overall health. While some people may not show any symptoms, vitamin D deficiency can sometimes cause:

• Muscle weakness or cramps

• Bone pain

• Fatigue

Vitamin D deficiency can be especially concerning for children, as they are growing and developing quickly.

Chronic vitamin D deficiency in children

Chronic vitamin D deficiency can result in a range of health issues such as:

• Rickets: A condition that causes soft, weak bones, which can lead to bowed legs and other skeletal deformities.

• Tooth decay: Insufficient vitamin D can weaken tooth enamel, increasing the risk of cavities.

• Stunted growth: Poor vitamin D levels may slow down both height and weight gain.

• Increased risk of fractures: Weak and soft bones are more prone to breaking.

• Muscle weakness and pain: A lack of vitamin D can affect muscle strength and function.

• Weakened immune system: Vitamin D plays a key role in supporting immune health.

Causes of vitamin D deficiency in children

One of the main causes of vitamin D deficiency in children is not getting enough through their diet. This can be due to dietary restrictions or preferences, such as: 

• Food allergies (especially to milk and dairy products)

• Picky eating habits

• Following a plant-based or vegan diet without proper supplementation

Another common cause is inadequate sun exposure, which limits the body’s ability to produce vitamin D through the skin. This is especially important since sunlight helps convert vitamin D into its active form. Children with darker skin tones are also at higher risk, since higher amounts of melanin (the pigment responsible for skin color) can reduce the skin’s ability to produce vitamin D from sunlight. 

Additionally, certain medical conditions can interfere with the body’s ability to absorb or process vitamin D, such as: 

• Celiac disease

• Inflammatory bowel disease (IBD)

• Liver disorders

• Other conditions affecting digestion, metabolism, or nutrient absorption

Vitamin D in food

Vitamin D is naturally found in only a few foods and in small amounts. Common dietary sources include:

• Fortified milk, yogurt, and dairy-free alternatives

• Fortified orange juice

• Fatty fish like salmon

• Fish with edible bones (like sardines)

• Cod liver oil

• Egg yolks

• Beef liver

For reference, 1 cup of fortified milk has about 100 to 120 IU of vitamin D, and children above age one need 600 IU per day.

Because vitamin D is essential for bone growth and development—and it’s difficult to get enough through food, the American Academy of Pediatrics (AAP) recommends that:

• Babies under 12 months who are breastfed or drinking less than 1 liter of formula daily should receive a vitaminD supplement every day.

• Children over 1 year old should also take a vitamin D supplement, since it is difficult to meet daily needs through food alone.

If you have questions about vitamin D, reach out to your local or Summer Health pediatrician or registered dietitian for support. Summer Health is a pediatric telehealth platform offering 24/7 care, providing answers for everything from urgent concerns to everyday questions about your child’s health.