Researchers wanted to know if babies who get more vitamin D in their first year of life grow up with more muscle mass. They followed 49 children from Montreal who received either a standard or higher dose of vitamin D as infants. Two years later, the children who got the higher dose had noticeably more muscle mass and were slightly taller and heavier. This suggests that vitamin D during infancy might help babies develop stronger, leaner bodies as they grow. However, the study was small and was cut short due to COVID-19, so scientists need to do more research to confirm these findings.

The Quick Take

  • What they studied: Whether babies who receive higher doses of vitamin D (1000 IU per day) during their first year develop more muscle mass compared to babies receiving standard doses (400 IU per day), and whether these differences stick around as they grow older.
  • Who participated: 49 toddlers in Montreal, Canada who were originally part of a vitamin D study when they were infants (1-12 months old). About half received the higher vitamin D dose and half received the standard dose. They were checked again at 24 months old.
  • Key finding: At age 2, children who received the higher vitamin D dose had about 1.2 pounds more muscle mass, were nearly an inch taller, and weighed about 2 pounds more than children who received the standard dose. These differences were statistically significant, meaning they were unlikely to be due to chance.
  • What it means for you: If confirmed by larger studies, this suggests that vitamin D supplementation during infancy might support healthy muscle development in young children. However, this is preliminary evidence from a small study, and parents should consult their pediatrician about appropriate vitamin D dosing for their babies rather than making changes on their own.

The Research Details

This was a follow-up study of an earlier vitamin D trial. Researchers had originally given infants either 400 IU or 1000 IU of vitamin D3 (a form of vitamin D) daily from ages 1 to 12 months. Two years after the original study ended, they brought back 49 of the original children (now 24 months old) to measure how much muscle and fat they had on their bodies using a special scanning machine called a DEXA scan. They also measured height, weight, and bone density. The researchers used statistical methods to compare the two groups and see if the differences they found during infancy were still there.

The study was originally designed to follow children until age 3, but the COVID-19 pandemic forced early closure, so the final measurements at 36 months couldn’t be completed. This is an important limitation because it means we don’t know if the benefits continued as children got older.

This research approach is valuable because it follows the same children over time, which helps researchers understand whether early nutrition choices have lasting effects. By measuring actual muscle mass with a DEXA scan rather than just estimating it from weight, the researchers got precise information. However, the small number of participants and early study closure mean the results need to be confirmed with larger, longer studies before making strong recommendations.

Strengths: The study used objective measurements (DEXA scans) rather than estimates, and it followed children over time. The journal (American Journal of Clinical Nutrition) is highly respected in nutrition science. Weaknesses: Only 49 children completed the follow-up (about half of the original group), which is a small sample size. The study ended early due to COVID-19, so we don’t have data on older children. There was no comparison group of children who didn’t receive vitamin D supplementation. These limitations mean the findings are interesting but not definitive.

What the Results Show

At 24 months of age, children who received 1000 IU of vitamin D daily as infants had significantly more lean muscle mass than those who received 400 IU. The difference was about 538 grams (roughly 1.2 pounds) of additional muscle. This difference was statistically significant, meaning it’s unlikely to have happened by chance.

Along with the extra muscle, the higher-dose group was also taller (about 2.4 centimeters or nearly 1 inch taller) and heavier (about 0.9 kilograms or 2 pounds heavier). They also had slightly more bone mineral content, suggesting stronger bones. These measurements all make sense together—children with more muscle tend to be taller and heavier.

Importantly, the researchers found that vitamin D blood levels, body fat, and developmental milestones (like walking and talking) were similar between the two groups. This suggests that the extra vitamin D specifically affected muscle and bone development, not overall growth or development.

Bone mineral content (a measure of bone strength) was about 25 grams higher in the higher-dose group, which is a small but statistically significant difference. This is encouraging because it suggests vitamin D may support bone development in addition to muscle development. However, vitamin D blood levels were not significantly different between groups at the 24-month follow-up, which is somewhat surprising and suggests the body may have adjusted to the different doses over time.

This study builds on the researchers’ earlier published work showing that infants receiving 1000 IU of vitamin D had more lean mass during the supplementation period (ages 1-12 months). The new finding is that these differences persisted at 24 months, suggesting the benefits don’t disappear once supplementation stops. This aligns with other research suggesting that early nutrition can have lasting effects on body composition. However, most previous studies on vitamin D in infants have focused on bone health rather than muscle development, so this research adds new information to the field.

The study has several important limitations. First, only 49 of the original 98 infants completed the follow-up, which is a relatively small sample size and raises questions about whether the results would hold in a larger group. Second, the study ended early due to COVID-19, so researchers couldn’t collect data at 36 months as originally planned, leaving questions about whether the benefits continue as children get older. Third, there was no control group of children who didn’t receive any vitamin D supplementation, making it harder to know if these differences are meaningful in the real world. Finally, all participants were from Montreal and were breastfed, so the results may not apply to formula-fed babies or children from other regions.

The Bottom Line

Based on this research, there is emerging but not yet conclusive evidence that vitamin D supplementation at 1000 IU daily (compared to 400 IU daily) during infancy may support lean muscle development. Current recommendations from pediatric organizations suggest breastfed infants receive 400 IU of vitamin D daily. This study suggests higher doses might have benefits, but larger, longer studies are needed before changing standard recommendations. Parents should discuss vitamin D supplementation with their pediatrician rather than making independent decisions. Confidence level: Low to Moderate—this is promising preliminary evidence that needs confirmation.

This research is most relevant to parents of breastfed infants, since formula-fed babies typically get vitamin D from their formula. Pediatricians and public health officials may find this interesting for future guideline development. This study should NOT prompt parents to give their babies higher vitamin D doses without medical guidance, as excessive vitamin D can be harmful. Anyone considering changes to infant nutrition should consult their pediatrician first.

In this study, differences in muscle mass were measurable at 24 months of age. If similar effects occur in other children, benefits would likely develop gradually over the first 2-3 years of life rather than appearing quickly. It’s unclear whether these differences would persist into later childhood or adulthood, as the study didn’t follow children beyond 24 months.

Want to Apply This Research?

  • For parents with infants currently receiving vitamin D supplementation, track the daily dose given (in IU) and note the date started. Record infant length and weight at regular pediatric checkups to monitor growth patterns over time. This creates a personal record to discuss with your pediatrician.
  • If your pediatrician recommends vitamin D supplementation for your breastfed infant, set a daily reminder to give the supplement at the same time each day (such as with morning feeding). Use the app to log when the supplement was given to ensure consistency and avoid missed doses.
  • Track your child’s growth measurements (height and weight) at each pediatric visit and log them in the app. Over months and years, you can see growth patterns and discuss them with your pediatrician. If your child is participating in any research studies, use the app to keep organized records of all measurements and follow-up appointments.

This research is preliminary and based on a small follow-up study that was cut short. The findings suggest vitamin D may play a role in muscle development but are not yet conclusive. Do not change your infant’s vitamin D supplementation without consulting your pediatrician. Current medical guidelines recommend 400 IU of vitamin D daily for breastfed infants. Excessive vitamin D can be harmful. This article is for educational purposes only and should not replace professional medical advice. Always consult with your child’s healthcare provider about appropriate supplementation and nutrition for your individual situation.