Predictive Factors of Vitamin D Inadequacy among Older Adults in the United States

Optimal serum vitamin D levels are reported to be associated with many health benefits; however, few studies have determined predictive factors using national level data. An assessment of predictive factors for vitamin D inadequacy was conducted using National Health and Nutrition Examination Survey (NHANES) 2001-2006 data. Using the study sample including adults aged 40 years or more, data analysis was performed using the weighted multivariate logistic regression statistical procedure. The prevalence of vitamin D inadequacy (serum vitamin D<20 ng/ml) was 37.3%. Non-Hispanic Blacks were 6.4 times more likely to demonstrate vitamin D inadequacy compared to non-Hispanic Whites (ORadj = 6.351; 95% CI 5.338, 7.555; p<0.0001). Also, female gender was a significant predictor of vitamin D inadequacy (ORadj = 1.499; 95% CI 1.315, 1.708; p<0.0001) in multivariate models. Subjects who reported not taking vitamin D supplements in the past 30 days were more than twice as likely to be vitamin D inadequate compared with those who had taken dietary supplements containing vitamin D (ORadj = 2.225; 95% CI 1.903, 2.601; p<0.0001). In conclusion, the strongest predictor of vitamin D inadequacy was non-Hispanic Black ethnicity. Other potential predictors included smoking, non-use of vitamin D supplements, abnormal BMI, collecting samples in winter, female gender, perception of own health condition as not excellent, lack of health care, and older age. More focused interventions targeting groups of United States residents with vitamin D inadequacy are needed.