title: History of diabetes mellitus and subsequent prostate cancer risk in the NIH-AARP Diet and Health Study.
abstract: OBJECTIVE
  A history of diabetes has been hypothesized to decrease prostate cancer risk, but studies have not always considered confounding or effect modification by dietary or lifestyle factors.
  
  
  METHODS
  We examined the association between diabetes history and subsequent prostate cancer risk in 328,316 men enrolled in the NIH-AARP Diet and Health Study. Participants were ages 50-71 years and without a prostate cancer diagnosis at baseline in 1995. A prior history of physician-diagnosed diabetes was assessed using a self-administered mailed questionnaire. Cases of prostate cancer were ascertained by matching the cohort to state cancer registries. Multivariable relative risks (RR) and 95% confidence intervals (CI) of prostate cancer were estimated using Cox regression.
  
  
  RESULTS
  During 5 years and 1,432,676 person-years of follow-up, 11,193 prostate cancer cases were ascertained. The age-adjusted and multivariable RRs of prostate cancer comparing men with diabetes to those without diabetes were 0.69 (95% CI=0.64, 0.74) and 0.71 (95% CI=0.66, 0.76), respectively, indicating no important confounding. The inverse association between diabetes and prostate cancer was particularly strong among men in the highest category of routine physical activity at work or home (RR=0.41; 95% CI=0.23, 0.74; p value for test of interaction = 0.03). Findings were similar for organ-confined and advanced prostate cancer.
  
  
  CONCLUSIONS
  Results from this large prospective study suggest that a history of diabetes is associated with a decreased risk of prostate cancer. The relationship strengthened with high levels of routine physical activity. Because increased physical activity is associated with lower circulating levels of insulin and testosterone, our findings support a role of hypoinsulinemia and low androgenicity linking diabetes to decreased prostate cancer risk.
authors: Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Institutes of Health, Department of Health and Human Services, 6120 Executive Blvd., EPS-MSC 7232, Bethesda, MD 20892, USA. brook.calton@ucsf.edu
authors: Brook A
authors: BA
authors: Calton
authors: Shih Chen
authors: SC
authors: Chang
authors: Margaret E
authors: ME
authors: Wright
authors: Victor
authors: V
authors: Kipnis
authors: Karla
authors: K
authors: Lawson
authors: Frances E
authors: FE
authors: Thompson
authors: Amy F
authors: AF
authors: Subar
authors: Traci
authors: T
authors: Mouw
authors: David S
authors: DS
authors: Campbell
authors: Paul
authors: P
authors: Hurwitz
authors: Albert
authors: A
authors: Hollenbeck
authors: Arthur
authors: A
authors: Schatzkin
authors: Michael F
authors: MF
authors: Leitzmann
mesh_terms: D002986:Clinical Trials as Topic; D015331:Cohort Studies; D003920:Diabetes Mellitus / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000150:complications* / Q000453:epidemiology* / Q000473:pathology; D012307:Risk Factors