Prevalence of Vitamin D inadequacy among postmenopausal North American women receiving osteoporosis therapy.

The Journal of clinical endocrinology and metabolism
Q1
Jun 2005
Citations:930
Influential Citations:16
Observational Studies (Human)
85
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Methods
Observational, cross-sectional, multicenter study of 1,536 postmenopausal North American women receiving osteoporosis therapy; mean age 71.1 ± 9.0 years; predominantly Caucasian; subjects recruited from 61 study sites; serum 25(OH)D and intact PTH measured; data collected via questionnaires; univariate logistic regression with multivariate stepwise logistic regression used to identify risk factors for vitamin D inadequacy (<30 ng/mL).
Intervention
Vitamin D supplementation; daily dosage categorized as <400 IU/day or 400 IU/day or more; duration not specified.
Results
Mean serum 25(OH)D was 30.4 ± 13.2 ng/mL; 52% had 25(OH)D < 30 ng/mL; 18% had < 20 ng/mL. Inadequacy was more common in those taking <400 IU/day than in those taking ≥400 IU/day (63% vs 45% below 30 ng/mL). Eight factors independently associated with inadequacy: age ≥80 years, nonwhite race, BMI ≥30 kg/m2, concomitant medications affecting vitamin D metabolism, not taking ≥400 IU/day vitamin D, lack of exercise, no prior physician discussion about vitamin D’s bone-health importance, and education below high school. Inadequacy ranged from 43% with one risk factor to 90% with five; 32% had zero risk factors. An inverse relationship existed between PTH and 25(OH)D; PTH rose when 25(OH)D < 29.8 ng/mL and plateaued beyond ~29.8 ng/mL. Conclusion: Vitamin D inadequacy is highly prevalent among this population; increasing daily vitamin D to at least 400 IU may reduce inadequacy, but optimal 25(OH)D targets remain uncertain; physician and public education about vitamin D to bone health is warranted.
Limitations
Cross-sectional design; cannot infer causality; winter-season data only; predominantly Caucasian sample; limited generalizability to non-White populations and to women not on osteoporosis therapy; reliance on self-reported supplement use; variability in 25(OH)D assays (two methods used) and potential measurement bias; residual confounding.

Abstract

PURPOSE To evaluate serum 25-hydroxyvitamin D [25(OH)D] concentrations and factors related to vitamin D inadequacy in postmenopausal North American women receiving therapy to treat or prevent osteoporosis. METHODS Serum 25(OH)D and PTH were obtaine...