BACKGROUND: Major reasons for long-term care insurance certification in Japan are stroke, dementia and fracture. These diseases are reported to be associated with calcium intake. This study examined the association between calcium intake and impaired activities of daily living (ADL) using the data from NIPPON DATA90, consisting of representative sample of the Japanese population. METHODS: A population-based nested case control study was performed. A baseline survey was conducted in 1990, followed by ADL surveys of individuals ≥65 years old in 2000. Individuals with impaired ADL and selected age- and sex-matched controls were then identified. We obtained 132 pairs. Calcium intake was energy-adjusted using the residual method. The association between calcium intake and impaired ADL was examined using conditional logistic regression models. To assess the accuracy of the estimates, we conducted bootstrap analyses. RESULTS: The adjusted odds ratios (ORs) for impaired ADL compared with the group with a calcium intake of <476 mg/day were 0.72 (95% confidence interval, 95% CI: 0.37-1.40) for the 476-606 mg/day group and 0.44 (0.21-0.94) for the ≥607 mg/day group in 2000 (P for linear trend = 0.03). After the bootstrap analyses, the inverse relationship unchanged (median OR per 100-mg rise in calcium intake: 0.87 [1,000 resamplings], 95% CI: 0.76-0.97). CONCLUSIONS: After bootstrap analyses, calcium intake was inversely associated with impaired ADL, 10 years after the baseline survey.