Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
The new study, which was performed in winter at 41° N, supported the recommended dose of 400 IU/day for supplements to raise 25(OH)D levels in the infants.
Researchers at the University of Iowa tested four different doses of vitamin D (200, 400, 600, or 800 International Units) in the mothers of 213 breastfed infants.
“At the time the study was initiated, the recommended dose of supplemental vitamin D was 200 IU/day,” explained Ekhard Ziegler, Steven Nelson, and Janice Jeter. “In its original design, the study was to test 200, 400, and 600 IU/day. The addition of a dose of 800 IU/day was deemed necessary when a number of infants showed 25(OH)D levels less than 50 nmol/l in spite of receiving vitamin D supplements.”
Start at birth?
The infants received the supplements from one month to nine months of age, and the 25(OH)D levels were found to increase in response to the supplements in a dose-dependent manner.
“Infant levels at 1 [month of age] were less than one-half of maternal levels,” noted the researchers. “Since at birth, infant levels were probably closer to maternal levels, this suggests that infant levels had fallen appreciably since birth. The high prevalence of low levels at 1 month strongly argues in favor of starting vitamin D supplementation soon after birth.”
Ziegler, Nelson, and Jeteradded that the supplements were not associated with any changes on the incidence of illness for the infants.
“The data support 400 IU/d as an [adequate intake], and agree with the current recommendation of 400 IU/day as a supplement for breastfed infants,” they concluded.
Source: Pediatric Research
Volume 76, Number 2, Pages 177-183. doi: 10.1038/pr.2014.76
“Vitamin D supplementation of breastfed infants: a randomized dose-response trial”
Authors: E.E. Ziegler, S.E. Nelson, J.M. Jeter