4.3.5 Nutrition: Milk intake in infancy will be assessed by weighing infants prior to and after breast-feeding (i.e., test weighing and the basis of the required weigh scales). For this purpose, parents will be provided with electronic weigh scales designed for test weighing over 3 days then returned to the research site by courier. Additionally, breast milk vitamin D (all forms) will be measured (using HPLC (51, 52)) in samples collected at inception and the 3 month visit using an electronic breast pump. Mothers will be asked to feed the infant on one breast and pump from the other. Total intake of vitamin D will then be derived from milk intake and milk vitamin D concentration. Thus total intakes of vitamin D will be possible whether breast-fed or fed formula.