Glycosylated hemoglobin and risk of colorectal cancer and adenoma (United States)

Objectives: The consistently observed epidemiologic associations of obesity and physical activity with colorectal cancer and precursor adenoma risk su ggest that insulin and glucose control may be contributory. We evaluated th e association of glycosylated hemoglobin (HbA(1c)), a clinical indicator of average glycemia over the previous 2 months, and possibly, indirectly, a m arker of average blood insulin level, with colorectal carcinogenesis. Methods: Among women in the Nurses' Health Study, who provided blood in 198 9-90 and were diagnosed subsequently in 1989-94, we included 79 colorectal cancer cases and 156 matched controls, and 201 distal colorectal adenoma ca ses and 201 matched controls. HbA(1c) concentrations in red blood cells wer e determined blindly by turbidometric immunoinhibition. Odds ratios (OR) an d 95% confidence intervals (CI) were estimated from conditional logistic re gression models. Results: HbA(1c) level did not significantly differ between colorectal canc er cases (median 5.5%) and controls (5.5%, p = 0.5), although a small diffe rence between adenoma cases (5.6%) and controls (5.5%, p = 0.06) was noted. Compared to the lowest tertile of HbA(1c) (median 5.2%), women in the midd le (median 5.5%, OR = 1.2, CI = 0.6-2.5) and upper (5.8%, OR = 1.2, CI = 0. 6-2.7) tertiles were not at an increased risk for colorectal cancer. A mode stly elevated risk of distal colorectal adenoma in the upper (median 5.8%, OR = 1.4, CI = 0.9-2.3) versus lower (median 5.3%) tertile could not be exc luded. These associations were not appreciably altered after adjusting for known and suspected colorectal cancer risk factors. Conclusion: Over the range of levels observed in this relatively small samp le of middle-aged women, prediagnostic HbA(1c) does not clearly predict col orectal cancer and adenoma risk.