I have yet to see a survey on what percentage of infants get adequate vitamin D supplementation. While I believe that the Food and Nutrition Board’s recommendation of 400 IU is inadequate, the Canadian Pediatric Association’s recommendation of 800 IU/day is much closer to what infants probably need, although no one is sure, since few researchers have measured vitamin D levels in infants and correlated them with total vitamin D intake.
In an attempt to see exactly how much vitamin D infants need, Dr. Pawel Pludowski of the Children’s Memorial Health Institute in Poland and nine colleagues studied 98 infants for 12 months, calculating their total vitamin D intake and measuring their vitamin D levels at age 6 and 12 months.
Pludowski P, Socha P, Karczmarewicz E, Zagorecka E, Lukaszkiewicz J, Stolarczyk A, Piotrowska-Jastrzebska J, Kryskiewicz E, Lorenc RS, Socha J. Vitamin D supplementation and status in infants: a prospective cohort observational study. J Pediatr Gastroenterol Nutr. 2011 Jul;53(1):93-9.