Low plasma coenzyme Q₁₀ levels and breast cancer risk in Chinese women

Background: Low circulating levels of coenzyme Q₁₀ (CoQ ₁₀) have been associated with increased cancer incidence and poor prognosis for a number of cancer types, while a recent prospective study observed a positive association for CoQ₁₀ with breast cancer risk. Methods: We prospectively examined the association of plasma CoQ₁₀ with breast cancer risk in a nested case-control study of Chinese women within the Shanghai Women's Health Study (SWHS). Prediagnostic plasma samples were obtained from 340 cases and 653 age-matched controls and analyzed for total CoQ₁₀. Results: A borderline significant inverse association for breast cancer incidence with plasma CoQ₁₀ level was observed by a conditional logistic regression model adjusted for age and age at first live birth, which became significant after elimination of cases diagnosed within 1 year of blood draw (P_trend = 0.03). This association was independent of menopausal status. Plasma CoQ₁₀ levels were also observed to be significantly associated with circulating γ-tocopherol (r = 0.50; P < 0.0001) and α-tocopherol (r = 0.38; P < 0.0001) levels. Conclusions: Circulating levels of CoQ₁₀ were generally low in this population and the observed association with breast cancer risk may be limited to those women with exceptionally low values. Impact: This study reports an inverse relationship between circulating CoQ₁₀ and breast cancer risk, while the only other prospective study of CoQ₁₀ and breast cancer to date found a positive association. Lower levels of CoQ₁₀ in the SWHS population suggest that the 2 studies may not be contradictory and indicate a possible nonlinear (U-shaped) association of CoQ₁₀ with risk.