This study investigates the association between early-life exposure to residential green space and bone mineral density (BMD) in children aged 4 to 6 years. The study is part of the ENVIRONMENT birth cohort, which recruited mother-child pairs from Flanders, Belgium, and followed them up for 4 to 6 years. Green space was estimated within various radii (100-3000 m) around the residence. Radial BMD was assessed using quantitative ultrasound at the follow-up visit. Key findings include: - Higher exposure to residential green space was associated with increased BMD. - An IQR increment in total green space (21.2%) and high green space (19.9%) within 500 m was associated with a significant increase in BMD. - Higher green space within 1000 m was associated with a lower risk of having low BMD. - The strongest associations were observed within a 500-m radius, with no significant associations at the closest buffer (100 m). The study highlights the importance of early-life exposure to residential green space on bone health during critical periods of growth and development. These findings suggest that interventions to increase access to green spaces could potentially reduce the risk of fracture and osteoporosis later in life.This study investigates the association between early-life exposure to residential green space and bone mineral density (BMD) in children aged 4 to 6 years. The study is part of the ENVIRONMENT birth cohort, which recruited mother-child pairs from Flanders, Belgium, and followed them up for 4 to 6 years. Green space was estimated within various radii (100-3000 m) around the residence. Radial BMD was assessed using quantitative ultrasound at the follow-up visit. Key findings include: - Higher exposure to residential green space was associated with increased BMD. - An IQR increment in total green space (21.2%) and high green space (19.9%) within 500 m was associated with a significant increase in BMD. - Higher green space within 1000 m was associated with a lower risk of having low BMD. - The strongest associations were observed within a 500-m radius, with no significant associations at the closest buffer (100 m). The study highlights the importance of early-life exposure to residential green space on bone health during critical periods of growth and development. These findings suggest that interventions to increase access to green spaces could potentially reduce the risk of fracture and osteoporosis later in life.