AGE AND RISK-FACTORS FOR COLON-CANCER (UNITED-STATES AND AUSTRALIA) -ARE THERE IMPLICATIONS FOR UNDERSTANDING DIFFERENCES IN CASE-CONTROL AND COHORT STUDIES

Data from two population-based case-control studies were used to inves tigate the effect of age on colon cancer risk. Dietary intake data wer e assessed from a study conducted in Utah (United States) between 1979 and 1983; reproductive data were assessed from a study conducted in A delaide (Australia) between 1979 and 1980. Data from both studies were assessed for their impact on those less than 65 years of age and thos e 65 or more years of age. Intake of energy, fat, and protein had a gr eater impact on risk among older men than among younger men. Risk esti mates for the upper quartile of intake relative to the lowest quartile of intake were 8.5 (95 percent confidence interval [CI] = 1.7-43.0) f or energy, 8.2 (CI = 1.6-41.3) for protein, and 7.2 (CI = 1.6-31.4) fo r total fat for older men, while comparable risk estimates were 2.4 (C I = 0.6-9.1) for energy, 3.0 (CI = 0.7-13.6) for protein, and 1.9 (CI = 0.5-7.1) for total fat among younger men. Similar trends were seen f or older women for energy and protein. beta-carotene decreased colon c ancer risk among younger men (odds ratio [OR] = 0.4, CI = 0.1-1.2) and women (OR = 0.1, CI = 0.1-0.5), although not among older men (OR = 1. 2, CI = 0.3-4.9) and women (OR = 1.9, CI = 0.6-64). Calcium decreased risk of colon cancer among older men (OR = 0.1, CI = < 0.1-0.8) and yo unger women (OR = 0.2, CI = < 0.1-0.7). Women who were diagnosed at ag e 65 or older and were nulliparous had a tenfold increase in colon can cer risk (CI = 2.4-47.9) relative to women who had an early age at fir st birth. Women diagnosed with colon cancer before age 65 did not expe rience an increase of colon cancer risk associated with being nullipar ous. These data suggest that age at diagnosis may interact with other factors to alter risk of colon cancer.