Calcium intake is widely recommended, but its association with mortality remains unclear. This study indicated higher levels of calcium intake were associated with lower mortality in American adults. However, a nonlinear association between calcium intake and mortality suggested that excessive calcium intake beyond a certain threshold may increase mortality risk. Purpose The study aimed to investigate the association of total, dietary, or supplemental calcium intake with all-cause, cardiovascular, and cancer mortality in American adults. Methods This prospective cohort study used the National Health and Nutrition Examination Survey from 2005 to 2018. Participants were categorized into tertiles based on calcium intake. Risks of all-cause, cancer, or cardiovascular mortality and the dose-response relationship were estimated using weighted Cox proportional hazard regression and restricted cubic splines, with adjustments for demographic characteristics, comorbidities, laboratory parameters, and dietary data. Results In total, 6172 participants were included (median age: 61 years), and 869 had died (CVD:217, cancer:224) during a median follow-up of 81 months. After adjusting for confounders, higher total calcium(>= 1660mg/d) [HR, 95%CI: 0.867 (0.865-0.869)], dietary calcium(>= 1075mg/d) [HR, 95%CI: 0.711 (0.709-0.713)], and supplemental calcium (>= 600mg/d) [HR, 95%CI: 0.786 (0.784-0.787)] intake groups were associated with lower all-cause mortality risk compared to the lowest intake group. Similar beneficial associations were found for cardiovascular, cancer mortality, and across subgroups of various ages, genders, races and body mass indexes. In the dose-response analysis, a 'J-shaped' nonlinear relationship was observed between calcium intake and the risk of all-cause, cardiovascular, and cancer mortality. Conclusions Higher levels of total, dietary, or supplemental calcium were associated with lower all-cause, cardiovascular, or cancer mortality. However, a nonlinear association between calcium intake and mortality suggested that excessive calcium intake beyond a certain threshold may increase mortality risk.