At each age, dietary and supplement intake will be documented in infants using written 3-day records that are designed to accommodate test weighing and documentation of other milks and any foods consumed as successfully used previously by the PI (53). Estimated portions sizes will be made using household measuring tools. Mothers will be asked about timing of introduction of solid foods or fluids other than breast-milk or vitamin D supplements. If infants wean to infant formula or cows milk, the product brand will be documented. It is anticipated that by 3 to 4 months of age that many infants will wean from breastfeeding to formula. However, the dosage will not be adjusted. Intake of vitamin D from infant formula, cows' milk etc will be documented and used to calculate total daily intake above the supplement. Such additional vitamin D will be addressed in the statistical analysis and is anticipated to be a systematic variation in total intakes.