Cinnamon and breast cancer: the picture is unclear
Cinnamon is a spice consisting of the inner bark of the cinnamon tree (Cinnamomum verum or Cinnamomum zeylanicum). Cinnamon is a dietary source of manganese, calcium and iron. It also contains salicylic acid and several carotenoids and proanthocyanidins, all of which may have chemopreventive activities. Cinnamon has been shown to have powerful anti-inflammatory, antifungal, antibacterial, insecticidal and antioxidant properties. Consumption of cinnamon has been shown to improve glucose metabolism, lowering blood sugar and reducing insulin resistance.
Cancer-related effects of consuming cinnamon
Cinnamon extract has been shown to inhibit vascular endothelial growth factor (VEGF), which is crucial to the formation of tumor blood vessels. Cinnamon treatment has also been found to inhibit the expression of regulators of tumor progression in melanoma cells. The same study found that cinnamon treatment enhanced the anti-tumor activities of a type of T cell whose functions include destroying tumor cells. Another study found that cinnamon extract reduced cellular proliferation of myeloid leukemia cells. However, no population studies have investigated the association between cinnamon consumption and risk of cancer. It is also possible that cinnamon's marked antioxidant, antifungal, antibacterial, and insecticidal properties derive in part from a somewhat toxic profile that would become more evident if large quantities of cinnamon were to be consumed.
Additional comments regarding cinnamon
Cinnamomum cassia or Cinnamomum aromaticum, which is also sold as cinnamon (but is considered inferior to true cinnamon) is made from the bark of a related tree. It is sometimes marketed as "Cassia," "Chinese cinnamon," "Vietnamese cinnamon," or "Indonesian cinnamon." Cassia has a stronger (some would say harsher) flavor than cinnamon and is more toxic to the liver at lower dosages as a result of its far higher coumarin content. One study that examined cassia's estrogenicity reported that cassia significantly induced the growth of estrogen receptor positive MCF-7 breast cancer cells compared to untreated MCF-7 cells. We would avoid cassia.