TORONTO -- A supplement of 400 international units of vitamin D each day is enough to ensure an infant's health for at least the first 12 months of life, Canadian researchers have determined after testing several dosage levels in babies.
Their study, published today in a special child-health issue of the Journal of the American Medical Association, found 400 IU daily is as good as doses of 800, 1,200 or 1,600 IUs at preventing rickets and promoting bone health.
"Right now, the dose that we're recommending is the 400, and that's to be given every day until the baby can achieve that amount from other foods, and typically we consider that more at one year of age," said co-principal researcher Hope Weiler of McGill University in Montreal.
Vitamin D is needed for healthy bones, and it's crucial that babies get enough during the first 12 months of life when bones are growing rapidly, said Weiler, a professor in the School of Dietetics and Human Nutrition.
However, recommendations about how much of the "sunshine vitamin" is needed to prevent rickets in infants vary widely around the world.
The researchers followed a group of 132 infants who were randomly assigned to receive one of four daily doses of vitamin D -- 400, 800, 1,200 or 1,600 IUs -- over 12 months. Most were breast-fed at the beginning of the study, though that proportion had dropped significantly by the time the babies were a year old. Tests repeated every three months measured how much vitamin D was in each infant's blood. That test provides a biomarker for how much vitamin D is stored in the liver, where it is converted to an active form that can be used by the body.
Researchers discontinued the 1,600 IU dose partway through the study because the blood levels were thought to be unnecessarily high, potentially putting infants in that group at risk for hypercalcemia, an excess of calcium.
The team also measured babies' weight, length and head circumference and used low-dose X-rays to look at skeletal growth and estimate mineral composition of the youngsters' bones.
Researchers found, as early as the three-month mark, there was no extra benefit from higher doses of vitamin D and that 400 IU per day was sufficient. Weiler said it's not known how much vitamin D a baby has received in the womb through maternal-fetal transfer or how much a mother supplies in her breast milk.
-- The Canadian Press