Association of plasma branched-chain amino acid levels with colorectal cancer risk in a nested case-control study.

Background: Intake of branched-chain amino acids (BCAA) has been suggested to have a prophylactic effect against carcinogenesis in colorectal cancer (CRC). However, the possible effect of plasma BCAA concentration has not been fully evaluated.

Methods: We conducted a prospective case-control study within a cohort of four public health center areas for which blood sample and questionnaire data from a 5-year follow-up survey were available. We identified 360 newly diagnosed CRC cases during the follow-up period and selected two matched controls for each case. We estimated odds ratio (OR) and 95% confidence intervals (CI) for CRC using conditional logistic regression models adjusted for potential confounding factors.

Results: Increased plasma concentrations of BCAAs were not inversely associated with CRC risk after adjustment for potential confounders. Compared with the lowest quartile, ORs in the highest quartile of leucine, isoleucine, valine, and total BCAA were 0.74 (95% CI, 0.49-1.12), 0.85 (0.56-1.29), 0.75 (0.50-1.13), and 0.70 (0.47-1.05), respectively. After excluding cases diagnosed within the first 6 years of follow-up, total BCAA and leucine were significantly related to a decreased risk of CRC, with ORs in the highest quartile of total BCAA and leucine of 0.58 (0.35-0.96) and 0.56 (0.33-0.93), respectively.

Conclusions: We found no statistically significant inverse association between plasma BCAA concentrations and CRC risk in overall analyses, whereas on 6-year exclusion, total BCAA and leucine were associated with decreased CRC risk. Plasma BCAA concentrations may play a prophylactic role in colorectal carcinogenesis, and further investigation is warranted.