Systematic review of physical activity and health in the early years (aged 0-4 years).

The early years represent a critical period for promoting physical activity. However, the amount of physical activity needed for healthy growth and development is not clear. Using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework, we aimed to present the best available evidence to determine the relationship between physical activity and measures of adiposity, bone and skeletal health, motor skill development, psychosocial health, cognitive development, and cardiometabolic health indicators in infants (1 month - 1 year), toddlers (1.1-3.0 years), and preschoolers (3.1-4.9 years). Online databases, personal libraries, and government documents were searched for relevant studies. Twenty-two articles, representing 18 unique studies and 12 742 enrolled participants, met inclusion criteria. The health indicators of interest were adiposity (n = 11), bone and skeletal health (n = 2), motor development (n = 4), psychosocial health (n = 3), cognitive development (n = 1), and cardiometabolic health indicators (n = 3); these indicators were pre-specified by an expert panel. Five unique studies involved infants, 2 involved toddlers, and 11 involved preschoolers. In infants, there was low- to moderate-quality evidence to suggest that increased or higher physical activity was positively associated with improved measures of adiposity, motor skill development, and cognitive development. In toddlers, there was moderate-quality evidence to suggest that increased or higher physical activity was positively associated with bone and skeletal health. In preschoolers, there was low- to high-quality evidence on the relationship between increased or higher physical activity and improved measures of adiposity, motor skill development, psychosocial health, and cardiometabolic health indicators. There was no serious inconsistency in any of the studies reviewed. This evidence can help to inform public health guidelines. (PROSPERO registration: CRD42011001243).