Research considering the relationship between dietary Mg and osteoporosis as well as fractures are sparse and conflicting. We therefore aimed to investigate Mg intake and the onset of fractures in a large cohort of American men and women involved in the Osteoarthritis Initiative over a follow-up period of 8 years. Dietary Mg intake (including that derived from supplementation) was evaluated through a FFQ at baseline and categorised using sex-specific quintiles (Q); osteoporotic fractures were evaluated through self-reported history. Overall, 3765 participants (1577 men; 2071 women) with a mean age of 60·6 (sd 9·1) years were included. During follow-up, 560 individuals (198 men and 368 women) developed a new fracture. After adjusting for fourteen potential confounders at baseline and taking those with lower Mg intake as reference (Q1), men (hazard ratio (HR) 0·47; 95 % CI 0·21, 1·00, P=0·05) and women (HR 0·38; 95 % CI 0·17, 0·82, P=0·01) in the highest quintile reported a significantly lower risk for fracture. Women meeting the recommended Mg intake were at a 27 % decreased risk for future fractures. In conclusion, higher dietary Mg intake has a protective effect on future osteoporotic fractures, especially in women with a high risk for knee osteoarthritis. Those women meeting the recommended Mg intake appear to be at a lower risk for fractures.