Summary Inositol hexaphosphate (InsP6 a.k.a. phytic acid or IP6) is ubiquitous. In the plant kingdom it is particularly abundant in cereals and legumes; in much smaller amounts IP6 and its lower phosphorylated forms (IP1−5) are contained in most mammalian cells, where they are important in regulating vital cellular functions. Both in vivo and in vitro experiments have demonstrated striking anticancer (preventive as well as therapeutic) effects of IP6. Inositol also is anti-carcinogenic, albeit to a lesser extent; it acts synergistically IP6 in inhibiting cancer. In addition to reduction in cell proliferation, IP6 increases differentiation of malignant cells often resulting in reversion to the normal phenotype. IP6 is quickly absorbed from the rat stomach and upper intestine and distributed as inositol and IP1. In vitro, it is instantaneously taken up by malignant cells undergoing variable dephosphorylation to inositol and IP1−5, pointing towards their role in mediating the action of IP6. In humans, IP6 has recently been detected in urine, plasma and other biological fluids; the levels fluctuating with ingestion or deprivation of IP6 or IP6-rich diet. As IP6 is high in high-fibre diets, these also may explain, at least in part, the epidemiological observation showing the association of ingesting high-fibre diets with a lower incidence of certain cancers. Along with safety, the reproducible efficacy of IP6 and inositol in the prevention of cancer in laboratory animals warrant their inclusion in our strategies for cancer prevention and perhaps therapy in humans. Aside from the anticancer action, IP6 and inositol also have numerous other health benefits. All these facts of normal physiological presence of IP6 in our body the level of which fluctuates with intake, association of an IP6-rich diet with low incidence of several diseases and vice versa, and finally reversal of some of these conditions, at least in part, by IP6 supplementation strongly argue in favour of its inclusion as an essential nutrient or perhaps a vitamin.