They were initially interested in confirming the importance of vitamin D for bone density when they uncovered the potential benefit of lower body fat.
“We were very intrigued by the higher lean mass, the possibility that vitamin D can help infants to not only grow healthy skeletons but also healthy amounts of muscle and less fat,” says Hope Weiler, director of the Mary Emily Clinical Nutrition Research Unit at McGill University.
Published in Pediatric Obesity, the study makes a connection for the first time between the benefits of achieving healthy vitamin D status during a baby’s first 12 to 36 months and how muscle mass develops.
Researchers followed up on a 2013 study in which 132 infants in Montréal, Québec, were given a vitamin D3 supplement at one of four different dosages between the ages of 1 month and 12 months.
The findings confirm the importance for the development of strong bones of a vitamin D supplement of 400 IU per day during a baby’s first year. Higher doses didn’t provide any additional benefit—at least not in terms of bone development.
The body scans used to assess bone density also allowed the team to measure children’s muscle and fat mass. While there were no significant differences in body composition across the different dosage groups, children who had vitamin D stores above the threshold recommended by the Canadian Pediatric Society averaged around 450 grams (or about 1 pound) less body fat at 3 years of age.
Vitamin D supplements are routinely recommended for babies until they can get an adequate amount through their diet. The skin synthesizes vitamin D when exposed to sunlight, making supplements all the more important during long winters.
Further, the findings show a correlation between lean muscle mass and the average level of vitamin D in the body over the first three years. The only other factor found to make a significant difference to the children’s amount of body fat was the level of physical activity.