1. Introduction
Evidence exists, which suggests that edible berries may have beneficial effects against several types of human cancers [1] and [2]. The anticancer potential of berries has been related to bioactive phytochemicals contained by the fruits, which include flavonoids and proanthocyanidins (PAs) [3]. The anticancer effects are at least partially mediated through inhibition of oxidative stress and inflammation [4]. Thus far, most berry research has been limited to in vitro and animal applications with very few human studies [5], [6], [7] and [8]. We have recently found that berry ingestion might provide cancer preventative benefits through modulation of natural killer cells (NK cells) [9], which represent a subset of peripheral lymphocytes that play a critical role in the innate immune response to virus-infected and tumor-transformed cells [10]. Specifically, in one of the first human studies investigating blueberries (BBs) and immune changes, we found that 250 g of BBs ingested daily for 6 weeks resulted in a significant doubling of NK cell counts in healthy marathon runners. It is thought that a better understanding of NK cell biology and function will broaden the applications for human cancer [11].