title: Association between stimulated plasma C-peptide and age: the Wadena City Health Study.
abstract: OBJECTIVE
  To assess age-related changes in stimulated plasma C-peptide in a population-based sample of adults.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Wadena, Minnesota, a city of 4,699 residents (1980 census) in west central Minnesota, approximately 150 miles from Minneapolis/St. Paul.
  
  
  METHODS
  344 non-diabetic subjects (NDDG standards) from a stratified random sample of the total adult population of Wadena, MN. The six-study strata were men and women from three age groups: young, 20-39 years of age; middle-aged, 40-59; and older, greater than 60 years of age.
  
  
  METHODS
  During a liquid meal of Ensure-Plus (Ensure-Plus challenge test; EPCT; Ross Laboratories), blood samples were taken for glucose, free fatty acids, creatinine, and C-peptide. Plasma C-peptide taken 90 minutes after the EPCT was used as a surrogate measure for insulin. Clinical tests included one-time samples for hemoglobin, glycosylated hemoglobin, plasma cholesterol, triglycerides, and lipoproteins. Physical measurements included height, weight, and blood pressure. Urine was assayed for C-peptide and creatinine. Assays of urine and plasma C-peptide used antibody M1221 (from Novo; Copenhagen, Denmark).
  
  
  RESULTS
  No differences were observed for the relationship between age and C-peptide within each of the three age groups for men and the three age groups for women. However, the levels of plasma C-peptide for older men or women were statistically significantly higher than levels for the young age groups of the same sex; fasting plasma glucose also was higher for older groups of both sexes, and postmeal glucose was significantly higher for older women. There were decreases with age in urine C-peptide clearance for women and men; the decline for women was statistically significant. In multiple regression models for men alone and women alone, that controlled for age, post-meal plasma glucose best explained plasma C-peptide levels. For young men, plasma glucose alone provided the best prediction of plasma C-peptide levels; body mass index (BMI) and plasma glucose provided the best prediction for young women. For older men and both middle-aged and older women, a combination of urine C-peptide clearance and plasma glucose best predicted plasma C-peptide levels; for middle-aged men, BMI also contributed to the prediction.
  
  
  CONCLUSIONS
  Secretion of insulin in response to an orally administered mixed meal is undiminished with age in non-diabetic adults.
authors.affiliation: Chronic Disease and Environmental Epidemiology Section, Minnesota Department of Health.
authors.forename: L R
authors.initials: LR
authors.lastname: French
authors.forename: F C
authors.initials: FC
authors.lastname: Goetz
authors.forename: A M
authors.initials: AM
authors.lastname: Martinez
authors.forename: J R
authors.initials: JR
authors.lastname: Boen
authors.forename: S A
authors.initials: SA
authors.lastname: Bushhouse
authors.forename: J M
authors.initials: JM
authors.lastname: Sprafka
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000097:blood* / Q000378:metabolism / Q000652:urine; D001786:Blood Glucose / Q000032:analysis; D015992:Body Mass Index; D002096:C-Peptide / Q000097:blood* / Q000652:urine; D002784:Cholesterol / Q000097:blood; D003404:Creatinine / Q000097:blood / Q000652:urine; D003430:Cross-Sectional Studies; D004435:Eating / Q000502:physiology*; D005215:Fasting; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D016018:Least-Squares Analysis; D016014:Linear Models; D008074:Lipoproteins / Q000097:blood; D008297:Male; D008875:Middle Aged; D008910:Minnesota; D011237:Predictive Value of Tests; D012737:Sex Factors; D014280:Triglycerides / Q000097:blood
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D002784:Cholesterol; D003404:Creatinine; D005230:Fatty Acids, Nonesterified; D006442:Glycated Hemoglobin; D006454:Hemoglobins; D008074:Lipoproteins; D014280:Triglycerides