title: Age and kidney function are the primary correlates of fasting plasma total homocysteine levels in non-diabetic and diabetic adults. Results from the 1999-2002 National Health and Nutrition Examination Survey.
abstract: BACKGROUND
  Plasma total homocysteine (tHcy) is commonly elevated in persons with diabetes. This may be due to effects of insulin and/or glucose and/or metabolic control on the metabolism or plasma levels of tHcy. This study examined the effects of fasting plasma glucose status on fasting tHcy levels among adults without diabetes, and diabetes per se among adults with a self-report history of diabetes.
  
  
  METHODS
  Analysis of data on adults (> or = 20y) who had fasted at least 8 hours, from the National Health and Nutrition Examination Survey (1999-2000 and 2001-2002). Subjects with no self-report history of diabetes were grouped according to fasting plasma glucose status as normal (< 100 mg/dL = NFG, n = 2,244), impaired (> or = 100 < 126 mg/dL = IFG, n = 1,108), or a provisional diagnosis of diabetes (> or = 126 mg/dL = DFG, n = 133). Subjects with a self-report history of diabetes (n = 275) were examined separately.
  
  
  RESULTS
  Fasting tHcy was higher (Ps < 0.01) among non-diabetic subjects with DFG and IFG, compared to NFG (median [95% confidence interval] = 8.6 [8.0-9.2], 8.3 [8.1-8.5], and 7.4 [7.3-7.5] micromol/L, respectively). Diabetic subjects had levels similar to non-diabetic subjects with DFG and IFG (8.3 [7.9-8.6] micromol/L). Age and estimated creatinine clearance were strong correlates of fasting tHcy among non-diabetic subjects (r = 0.38 to 0.44 and r = -0.35 to -0.46, respectively) and diabetic subjects (r = 0.41 and r = -0.46, respectively) (Ps < 0.001), while fasting glucose and glycohemoglobin (HbA1c) were weaker (but still significant) correlates of tHcy in non-diabetic and diabetic subjects. Fasting glucose status was not a significant independent predictor of fasting tHcy levels in non-diabetic subjects, and HbA1c was not a significant independent predictor of tHcy in diabetic subjects (Ps > 0.05).
  
  
  CONCLUSIONS
  Fasting tHcy levels are elevated among non-diabetic adults with elevated fasting glucose levels, compared to persons with normal fasting glucose levels, and among diabetic adults. However, elevations in fasting tHcy appear to be mediated primarily by age and kidney function, and not by measures of glucose metabolism.
authors.affiliation: Department of Epidemiology, Interdisciplinary Graduate Program in Nutritional Sciences, University of Washington, Seattle, WA 98195, USA. duncag@u.washington.edu
authors.forename: Glen E
authors.initials: GE
authors.lastname: Duncan
authors.forename: Sierra M
authors.initials: SM
authors.lastname: Li
authors.forename: Xiao-Hua
authors.initials: XH
authors.lastname: Zhou