A study on approximately 1,000 Finnish infants: a higher dose of supplemental vitamin D has no health benefits

Because vitamin D increases bone strength, for example, regular supplemental vitamin D is recommended for children In Finland. A triple daily dose did not lead to increased bone strength or to decreased infection incidence in the first 2 years of life, however, found the joint study of the Children's Hospital, the Pediatric Research Center and the University of Helsinki.

In Finland, supplemental vitamin D was introduced almost a hundred years ago to prevent rickets. The most optimal dose for the growth and health of small children has remained unclear, however.

Infants at the Kätilöopisto Maternity Hospital followed up for 2 years

The researchers wanted to study the effect of the vitamin D dose on the bone development and the susceptibility to infections. Families were interested in joining the study, and 975 healthy infants born at the Kätilöopisto Maternity Hospital in Helsinki were recruited during 2013–2014 and followed up until the age of two.

The healthy newborns were randomized to two groups. One of the groups received 10 micrograms of vitamin D supplement per day from the age of two weeks, in line with the normal child health clinic guidelines. The infants in the other group received 30 micrograms of vitamin D.

The study subjects and the researchers did not know which dose was given to each child. The family gave the vitamin dose to the child regularly at home as instructed, until the age of two. The families also kept a diary on the child's infections.

Children need vitamin D for growth and development

“Vitamin D affects the child's growth and development in many ways and it also regulates the function of the immune system. In this study, a higher dose of vitamin D did not bring any additional benefits but it also had no adverse effects during the two-year follow-up,” says Jenni Rosendahl, paediatrician from the Children’s Hospital.

At the age of two, bone density was measured using cross-section images of the tibia. The families kept a diary to monitor infection frequency.

“At the beginning of the study, we measured the infants' vitamin D level in the cord blood. The study infants had a good 25-hydroxy vitamin D level already at baseline. This finding reflects the situation where most of the Finnish pregnant mothers use a vitamin D supplement, as instructed by the maternity clinic.”

The recommended dose of supplemental vitamin D for pregnant women is 10 micrograms per day. For children under two years of age, the recommended dose is 10 micrograms, and for children aged 2–17 years, it is 7.5 micrograms per day. In Finland, vitamin D is also added to foodstuffs, such as dairy products, margarine and light spreads.

Does vitamin D affect allergies?

“We are very grateful for the families who committed to this study and took the trouble of filling in the follow-up forms and making follow-up visits to the Kätilöopisto Hospital. The children were subjected to frequent blood tests, bone densitometry and other tests,” says Jenni Rosendahl.

In the future, the researchers want to utilise this unique group of 975 children to find out what effects early vitamin D intervention has later in the life. Is it associated with allergy or asthma incidence or the development of autoimmune diseases, for example?

Further information:
Jenni Rosendahl, paediatrician, tel. +358 40 6477211 

Effect of Higher vs Standard Dosage of Vitamin D3 Supplementation on Bone Strength and Infection in Healthy Infants. A Randomized Clinical Trial. JAMA Pediatr. 2018;172(7):646–654.

The scientific community of the Pediatric Research Center of the Helsinki University Hospital produces approximately 300 peer-reviewed articles and ten dissertations annually. The scientific community consists of some 30 research groups from all fields of paediatric medicine. The researchers annually receive some 70 research permits.

Text by Vuokko Maria Nummi