Soil can affect human health in several ways leading either to specific diseases or to more general ill health. Some illnesses are caused by people's eating soil (geophagia), or by their inhaling it which can lead to malignancy if the soil contains asbestiform minerals; pathogens in the soil can lead to tetanus and infestations of hookworm, and particles may enter the body through abrasions and cause a form of elephantiasis. Radon from the soil is implicated in some cancers, and poorly drained soil has been linked recently with infant mortality. Most examples of ill health associated with the soil are caused by concentrations of elements in food or water that are either deficient or toxic. These elements include aluminium, arsenic, cadmium, copper, fluorine, iodine, lead, selenium, thallium and zinc. Their concentrations might reflect the natural condition of the soil, or the effects of people's actions, such as pollution. In isolated subsistence communities that grow their own food, distinct relations between elements and the aetiology of diseases can be identified. Examples include Keshan disease caused by selenium deficiency, and itai-itai disease caused by excess cadmium. Some of the relations between soil and health are uncertain and the causes putative, and they require further research to validate them They include the association of heart disease with poor acid soil, as in the glaciated regions of northern Europe and the coastal plain of the eastern United States of America. Even for well-defined relations it is evident that many are more complex than was originally thought, however, and greater understanding will require multidisciplinary investigation.
