title: Serum 25-hydroxyvitamin D status of the US population: 1988-1994 compared with 2000-2004.
abstract: BACKGROUND
  Changes in serum 25-hydroxyvitamin D [25(OH)D] concentrations in the US population have not been described.
  
  
  OBJECTIVE
  We used data from the National Health and Nutrition Examination Surveys (NHANES) to compare serum 25(OH)D concentrations in the US population in 2000-2004 with those in 1988-1994 and to identify contributing factors.
  
  
  METHODS
  Serum 25(OH)D was measured with a radioimmunoassay kit in 20 289 participants in NHANES 2000-2004 and in 18 158 participants in NHANES III (1988-1994). Body mass index (BMI) was calculated from measured height and weight. Milk intake and sun protection were assessed by questionnaire. Assay differences were assessed by re-analyzing 150 stored serum specimens from NHANES III with the current assay.
  
  
  RESULTS
  Age-adjusted mean serum 25(OH)D concentrations were 5-20 nmol/L lower in NHANES 2000-2004 than in NHANES III. After adjustment for assay shifts, age-adjusted means in NHANES 2000-2004 remained significantly lower (by 5-9 nmol/L) in most males, but not in most females. In a study subsample, adjustment for the confounding effects of assay differences changed mean serum 25(OH)D concentrations by approximately 10 nmol/L, and adjustment for changes in the factors likely related to real changes in vitamin D status (ie, BMI, milk intake, and sun protection) changed mean serum 25(OH)D concentrations by 1-1.6 nmol/L.
  
  
  CONCLUSIONS
  Overall, mean serum 25(OH)D was lower in 2000-2004 than 1988-1994. Assay changes unrelated to changes in vitamin D status accounted for much of the difference in most population groups. In an adult subgroup, combined changes in BMI, milk intake, and sun protection appeared to contribute to a real decline in vitamin D status.
authors.affiliation: National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD 20782, USA. acl1@cdc.gov
authors.forename: Anne C
authors.initials: AC
authors.lastname: Looker
authors.forename: Christine M
authors.initials: CM
authors.lastname: Pfeiffer
authors.forename: David A
authors.initials: DA
authors.lastname: Lacher
authors.forename: Rosemary L
authors.initials: RL
authors.lastname: Schleicher
authors.forename: Mary Frances
authors.initials: MF
authors.lastname: Picciano
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Yetley
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D015992:Body Mass Index; D050071:Bone Density Conservation Agents / Q000008:administration & dosage*; D002648:Child; D003430:Cross-Sectional Studies; D003611:Dairy Products; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D009752:Nutritional Status; D011159:Population Surveillance; D011863:Radioimmunoassay; D017678:Sex Distribution; D013473:Sunscreening Agents / Q000009:adverse effects; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood; D055815:Young Adult
chemical_list: D050071:Bone Density Conservation Agents; D013473:Sunscreening Agents; D014807:Vitamin D; C104450:25-hydroxyvitamin D