Whereas severe deficiency of vitamins and minerals required for life is relatively uncommon in developed nations, modest deficiency is very common among residents of the United States and Europe. Joyce C. McCann and Bruce N. Ames, from the Children's Hospital Oakland Research Institute (California, USA), examined moderate selenium and vitamin K deficiency to show how damage accumulates over time as a result of vitamin and mineral loss, leading to age-related diseases.  Compiling and assessing several general types of scientific evidence, the team tested whether selenium-dependent proteins that are essential from an evolutionary perspective are more resistant to selenium deficiency than those that are less essential. They discovered a highly sophisticated array of mechanisms at cellular and tissue levels that, when selenium is limited, protect essential selenium-dependent proteins at the expense of those that are nonessential. They also found that mutations in selenium-dependent proteins that are lost on modest selenium deficiency result in characteristics shared by age-related diseases including cancer, heart disease, and loss of immune or brain function. Explaining that their results should inform attempts to locate mechanistic linkages between vitamin or mineral deficiencies and age-related diseases by focusing attention on the vitamin and mineral-dependent proteins that are nonessential from an evolutionary perspective, the researchers conclude that: “Modest [selenium] deficiency is common in many parts of the world; optimal intake could prevent future disease.”