Long-Term Low Intake of Dietary Calcium and Fracture Risk in Older Adults With Plant-Based Diet: A Longitudinal Study From the China Health and Nutrition Survey

The aim of this longitudinal study was to investigate long-term associations between low dietary calcium intake and fracture risk in older adults with plant-based diet. Data of self-reported first fracture events of any type from 6210 Chinese men and women, aged 50 years or older and free from fracture at baseline, in a subcohort based on the China Health and Nutrition Survey (CHNS), were analyzed. Diet was repeatedly assessed by a combination of three consecutive 24-hour individual dietary recalls and a weighing and measuring of household food inventory in each round. The older men and women habitually ingested mean (SD) of 415 (147) mg/d and 373 (140) mg/d of calcium from plant-based diet, respectively. During a median follow-up of 7.0 years, 127 men (4.34%) and 232 women (7.06%) experienced first fracture events. The crude rates were 4.88, 2.55, and 6.83 per 1000 person-years at risk for men, and 6.72, 7.10, and 11.0 per 1000 person-years at risk for women in the lowest, third, and highest quintile of dietary calcium intake. In nonlinear regressions, an increased risk of fracture was associated with dietary calcium intake more than 778 mg/d (multivariable adjusted hazard ratio [HR] 2.10, 95% confidence interval [CI] 1.00-4.41) or lower than 275 mg/d (1.74, 95% CI 1.00-3.01) for men and more than 651 mg/d for women (1.54, 95% CI 1.00-2.38). A nonsignificant trend of increase in fracture risk was found below 248 mg/d (1.00, 95% CI 0.67-1.50) in women using restricted cubic spline Cox regression. A relatively low fracture risk is observed in men with dietary calcium intakes of 275 to 780 mg/d and in women with intakes of 250 to 650 mg/d, and higher intakes may have no further benefit for fracture prevention. The patterns of dietary calcium with fracture risk are U-shaped in men and possibly in women. (C) 2016 American Society for Bone and Mineral Research.