The study evaluates trends in vitamin D insufficiency in the US population from 1988 to 2004 using data from the Third National Health and Nutrition Examination Survey (NHANES III) and NHANES 2001-2004. The mean serum 25-hydroxyvitamin D (25(OH)D) level decreased from 30 ng/mL in NHANES III to 24 ng/mL in NHANES 2001-2004. The prevalence of 25(OH)D levels below 10 ng/mL increased from 2% to 6%, while the prevalence of levels above 30 ng/mL decreased from 45% to 23%. Racial/ethnic disparities persisted, with non-Hispanic blacks having a higher prevalence of insufficiency. The findings suggest that current vitamin D supplementation recommendations are inadequate to address the growing epidemic of vitamin D insufficiency, particularly in non-Hispanic black populations. Increased intake of vitamin D and judicious sun exposure are recommended to improve overall health.The study evaluates trends in vitamin D insufficiency in the US population from 1988 to 2004 using data from the Third National Health and Nutrition Examination Survey (NHANES III) and NHANES 2001-2004. The mean serum 25-hydroxyvitamin D (25(OH)D) level decreased from 30 ng/mL in NHANES III to 24 ng/mL in NHANES 2001-2004. The prevalence of 25(OH)D levels below 10 ng/mL increased from 2% to 6%, while the prevalence of levels above 30 ng/mL decreased from 45% to 23%. Racial/ethnic disparities persisted, with non-Hispanic blacks having a higher prevalence of insufficiency. The findings suggest that current vitamin D supplementation recommendations are inadequate to address the growing epidemic of vitamin D insufficiency, particularly in non-Hispanic black populations. Increased intake of vitamin D and judicious sun exposure are recommended to improve overall health.