Single nucleotide polymorphisms (SNPs) account for 90% of all polymorphisms in humans. There are about 3 million SNPs in the human genome (1 per 1,000 nucleotides), two thirds of which are in non-coding DNA. Mutations that affect the composition of proteins involved in iron metabolism may have an impact on human health. There are no active pathways for iron excretion, therefore regulation of iron absorption is the primary determinant of iron balance; tightly controlled homeostatic mechanisms exist to ensure that sufficient iron is acquired and retained by the body and excess iron is not accumulated. Rare genetic mutations and knock-out animal models have been invaluable tools for elucidating the molecular events controlling iron metabolism (see reviews , ) but more common SNPs have a wider impact in both public health and personalised nutrition. The C282Y mutation of the HFE gene (chromosome 6), carried in approximately 13% of individuals from predominantly Caucasian populations, is closely associated with the iron-loading disease, hereditary haemochromatosis, but its mechanism of action is not clear, and the low penetrance  suggests that there may be other modifier genes.