A new prospective study has reported that women who go on to develop breast cancer are more likely to have very low levels of coenzyme Q10 (CoQ10) than those who don't. The study was designed to investigate the association between circulating CoQ10 and risk of breast cancer among a subset of women in the Shanghai Women's Health Study. Low plasma levels of CoQ10 have been reported to be associated with increased incidence and poor prognosis for a variety of cancer types. However, a recent prospective study found increased breast cancer risk among women with higher levels of CoQ10.

In the study, blood had been drawn from 340 breast cancer cases before their diagnoses, as well as from 653 age-matched cancer-free controls. These samples were analyzed for CoQ10. The women who went on to develop breast cancer were more likely to have had very low levels of CoQ10. This association held for both premenopausal and postmenopausal women. Plasma CoQ10 levels were also observed to be significantly associated with circulating vitamin E levels ((γ-tocopherol and α-tocopherol).

Generally speaking, levels of CoQ10 were low in this population and, the authors comment, the observed association with breast cancer risk may be limited to those women with exceptionally low values. The authors conclude that the study findings indicate an inverse relationship between circulating CoQ10 and breast cancer risk, whereas the only other prospective study of CoQ10 and breast cancer to date found a positive association. Generally low levels of CoQ10 in the Shanghai Women's Health Study participants may mean that the two studies are not necessarily contradictory, indicating a possible U-shaped association of CoQ10 with risk (with both low and high levels of CoQ10 potentially contributing to increased breast cancer risk).

Comments regarding the study

CoQ10, an essential nutrient, is valued primarily for its cardioprotective properties. CoQ10 has been reported to be positively associated with prognosis in heart failure; patients achieving higher plasma CoQ10 levels in intervention trials have been found to have better clinical outcomes. CoQ is synthesized in the body, but is also obtained in the diet, with meat products being the largest source in the U.S. diet (fish, fish oils, and the germ of whole grains are also sources). Perhaps not surprisingly, circulating CoQ10 correlates positively with total cholesterol and LDL (bad) cholesterol. Statin-induced depletion of CoQ10 levels has been reported.

The average U.S. diet provides approximately 10 mg per day of CoQ10 (obviously, intake can vary greatly). CoQ10 in supplement form tends to have low bioavailability and doses of 30 to 60 mg per day have been recommended to maintain normal serum concentrations of 0.7 to 1.0 g/mL. However, higher doses have been advocated for the treatment of heart disease to achieve serum concentrations of 2.0 to 3.0 g/mL, which have been reported by some investigators to have a beneficial impact on cardiovascular health.

Some observers have suggested that CoQ10 supplementation be used protect the heart from anthracycline chemotherapy, which is known to result in heart damage for a substantial minority of patients. However, taking CoQ10 during treatment for breast cancer appears inadvisable, based on current research. Increased concentrations of CoQ10 (due to increased biosynthesis) have been found in cancer cell lines after treatment with doxorubicin (Adriamycin) and other chemotherapy drugs. Such increase in CoQ10 appears to be part of the cellular defense against chemotherapy treatment, and may contribute to cancer cell survival.