Bone strength in early childhood : Associations with vitamin D and motor development

Bone health during childhood has gained attention, as early bone mass accrual significantly influences skeletal health in adulthood. Higher peak bone mass achieved in early life is considered protective against osteoporosis and fractures later in life. Various factors, including genetics, diet, physical activity, and early motor development, influence bone health. Mechanical loading through weight-bearing activities stimulates bone modeling and remodeling. Vitamin D is essential for bone health, and its deficiency has long been associated with rickets and impaired bone mineralization. Despite widespread recommendations for supplementation, vitamin D deficiency remains common in infancy worldwide. While optimal blood vitamin D concentrations are debated, a lower limit of 50 nmol/L and an upper threshold of 125 nmol/L have been suggested. Excess vitamin D intake, however, can lead to toxicity. The main aim of this doctoral thesis was to compare the effects of a standard daily vitamin D supplementation dose of 10 µg and a higher daily dose of 30 µg on bone strength in infants at 12 and 24 months of age. As secondary objectives, the study assessed the safety of higher vitamin D intake and examined how motor development, particularly the age at onset of independent walking, was associated with tibial bone strength parameters in infancy. In addition, this thesis provided novel data on the use of peripheral quantitative computed tomography (pQCT) imaging technique in infants, an area where research has previously been limited. This work is based on data from the Vitamin D Intervention in Infants (VIDI) study, which included 975 healthy, term born Finnish infants. They were randomized to receive daily vitamin D supplementation of either 10 µg or 30 µg for the first two years of life. Bone strength was assessed at 12 and 24 months using pQCT, a non-invasive imaging method that provides indirect estimates of bone strength. The measurements focused on the structural and density properties of the left tibia, including bone mineral content (BMC), volumetric bone mineral density (vBMD), cross-sectional area (CSA), polar moment of inertia (PMI), and periosteal circumference (PsC). Vitamin D concentrations were determined at birth and at follow-up visits at 12 and 24 months. Ionized calcium and parathyroid hormone were also measured at 12 and 24 months. Data on motor development were collected through parent-completed questionnaires. Nearly all children were born with sufficient vitamin D levels, and most of them maintained concentrations within the recommended reference range (50–125 nmol/L). At 12 and 24 months of age, only about 1% of children had serum vitamin D concentrations below 50 nmol/L. However, 17% at 12 months and 21% at 24 months exceeded the upper reference limit of 125 nmol/L, with 96% of these children belonging to the 30 µg group. Both supplementation doses were well tolerated. No signs of severe hypercalcemia or other adverse effects were observed. The use of the pQCT method produced new reference data that can be used in future pediatric bone studies. No significant differences in bone parameters were found between the 10 µg and 30 µg vitamin D groups, indicating that a higher vitamin D intake did not provide additional skeletal benefits in vitamin D-sufficient children. In contrast, the age at the onset of independent walking was strongly associated with bone outcomes at both 12 and 24 months. Earlier walkers had significantly higher BMC, CSA, PMI, and PsC. These findings show that both the 10 µg and 30 µg daily vitamin D doses are safe, but a daily dose of 10 µg is sufficient to maintain serum vitamin D levels adequate in healthy Finnish children during the first two years of life. Higher daily intake of 30 µg did not improve tibial bone strength, as measured with pQCT. Moreover, these findings highlight the importance of early mechanical loading for optimizing bone mass and geometry in early life.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2025

Author dc:creator

• Valkama, Saara

• lääketiede

Statement dc:rights

• This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
• Publikationen är skyddad av upphovsrätten. Den får läsas och skrivas ut för personligt bruk. Användning i kommersiellt syfte är förbjuden.

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/600690

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F600690