Rising phytate and oxalate intake, declining calcium intake, and bone health in United States adults: 1999-2023, a serial cross-sectional analysis.

BACKGROUND

The relationship among dietary patterns, calcium bioavailability, and bone health in United States adults remains unclear.

OBJECTIVES

This study aims to examine associations among dietary calcium, phytate, and oxalate intake and calcium bioavailability and bone health indicators, including bone mineral density (BMD), osteoporosis prevalence, and fracture incidence.

METHODS

A serial cross-sectional analysis was conducted using National Health and Nutrition Examination Survey (NHANES) data (1999-2023) for adults aged 18-85. Serum calcium and BMD were measured in NHANES laboratories; dietary intake, osteoporosis, and fracture history were self-reported. Primary exposures included dietary calcium, phytate, and oxalate; outcomes included estimated calcium absorption, and changes in BMD, osteoporosis, and fractures. Survey-weighted regression models were used to assess temporal changes and associations across survey cycles.

RESULTS

In 2017-2020, mean phytate intake was significantly higher than in 1999-2000 (834.1 ± 26.2 mg/d compared with 593.5±23.2 mg/d), and oxalate intake increased from 241.5 ± 6.6 mg/d to 280.5 ± 6.6 mg/d. Calcium intake peaked at 1025.3 ± 9.7 mg/d in 2009-2010 but lowered to 899.9 ± 15.7 mg/d by 2021-2023. Periods of lower calcium intake and higher phytate and oxalate concentrations corresponded with reduced calcium absorption. Milk consumption, a primary source of bioavailable calcium, decreased from 0.95 ± 0.03 cup-equivalents/d in 1999-2000 to 0.56 ± 0.02 in 2017-2020. Serum calcium concentrations lowered from 9.46 ± 0.02 mg/dL in 2009-2010 to 9.29 ± 0.01 mg/dL in 2017-2020. BMD at the femur dropped from 0.982 ± 0.004 to 0.934 ± 0.005 g/cm, and at the femoral neck from 0.849 ± 0.003 to 0.775 ± 0.005 g/cm between 2009-2010 and 2017-2020. Osteoporosis prevalence increased, and fractures at the hip, wrist, and spine were more frequently reported in 2017-2020 compared with those in 2009-2010.

CONCLUSIONS

Diets with greater phytate and oxalate and lower calcium and dairy intake may contribute to reduced calcium bioavailability and unfavorable bone health outcomes among United States adults.