Vitamin D in children: why supplementation remains essential beyond the first few months?

It is a fat-soluble vitamin, essential to several key functions:

• supporting bone growth and dental mineralisation through improved absorption of calcium and phosphorus,
• regulating calcium and phosphorus levels in the blood,
• supporting the functioning of the immune system,
• preventing rickets, a bone disease linked to vitamin D deficiency, which can lead to deformities and growth delays.

There are three ways to meet vitamin D requirements: sun exposure, diet, or medical supplementation. 

Vitamin D synthesis depends on sun exposure. However, in newborns and young children, this exposure is limited for safety reasons. Moreover, dietary intake alone is not sufficient to meet requirements. Breast milk, although excellent from a nutritional standpoint, is naturally low in vitamin D. Infant formula does contain it, but not always in adequate quantities.

For these reasons, health authorities recommend systematic supplementation from birth and throughout childhood, regardless of feeding method.

According to the National Nutrition and Health Programme (PNNS), the recommended daily intakes are as follows:

• from 0 to 2 years: 400 to 800 IU per day,
• beyond that: doses are adjusted according to sun exposure, diet, and medical advice.

As a result, it is impossible to meet their needs without supplementation. This is why health authorities recommend a daily intake from birth and throughout childhood, whether the baby is breastfed, bottle-fed, or already on solid foods.

The prescription should be tailored by the paediatrician or GP according to age, feeding method, and season.

A vitamin D deficiency can lead to:

• muscle weakness,
• bone fragility and an increased risk of fractures,
• rickets (growth disorders and bone deformities),
• weakened immunity.

Conversely, an excess intake can cause hypercalcaemia (excess calcium in the blood), which can lead to kidney, cardiac, or digestive problems (nausea, vomiting, weight loss, fatigue).

While supplementation remains essential for infants and young children, certain foods are good natural sources of vitamin D:

• oily fish (salmon, sardine, mackerel, herring)
• egg yolk
• liver
• mushrooms (chanterelles, porcini, morels, shiitake)
• dairy products or cereals fortified with vitamin D

These foods can be gradually introduced during weaning (from 4–6 months).