Callahan has suggested that geophagia may be a means by which the gut diversifies its microorganism flora. Such stimulation may be provided by ingesting a variety of microorganisms and their broken down components via pica, especially geophagia. From various epidemiological and laboratory lines of evidence, there is an emerging understanding of the advantages of the innate immune system being stimulated by pathogens and their component parts, and how they protect against allergic and autoimmune conditions. 19,20 The farm environment offers many exposures to a wide range of microorganisms and their broken down components, and so, this effect of farm life has been seen as another manifestation of the hygiene hypothesis. 18Įpidemiological studies following Strachan’s work have shown that prenatal and early childhood exposure to farm life reduces allergic illness. This led Strachan to conclude that the frequent infections passed between children in large households protected against the development of allergic conditions such as hay fever and eczema. The original hygiene hypothesis was based on the observation that hay fever was less common in children with more siblings in particular, the greater the number of older siblings, the stronger was this effect. This is basically an extension of the hygiene hypothesis. 7–11,17Īn emerging theory for the explanation of pica is that it serves useful immune functions by the ingested microorganisms stimulating the innate immune system, resulting in less response to allergens and autoantigens. Iron and zinc deficiency are the most frequently quoted associations with pica. 15,16 There are physiological theories based on the frequent observation that certain micronutrient deficiencies are associated with pica. This is the so-called organoleptic model. Another frequent observation is that for some groups, the taste and texture of soil in the mouth has an overwhelming appeal. In some populations it is considered abnormal, and possibly dangerous, not to eat soil in pregnancy. Many explanations have been offered for pica, some of which may only relate to certain populations. 6 At its most extreme, pica can result in intestinal obstruction. Further, as iron deficiency develops, activity of the duodenal divalent cation pump increases, resulting in more efficient uptake of the ingested lead. The soil supplies the ingested lead and at the same time, by binding ingested iron, results in less iron being available to compete with lead for transport across the duodenal mucosa. In polluted environments, the relationship between iron deficiency, geophagy and lead poisoning becomes complex. 7–11 As the minerals in soil can reduce absorption of micronutrients such as iron, geophagy makes the deficiency worse. 5,6 Furthermore, geophagy is frequently associated with iron deficiency. Pica can have various health effects one of the more commonly reported ones is the lead poisoning of earth-eating children who live in lead-polluted environments. There are also a number of conditions that are frequently associated with pica, including anaemia, renal disease and intellectual impairment. Pica is most common among children and pregnant women, two groups that are at most risk if the eaten substances contain pollutants. The most commonly described forms of pica are geophagy (earth), amylophagy (raw starch) and pagophagy (ice). 2,4 Finally, the behaviour must persist beyond 18 months to 2 years of age to distinguish it from infant mouthing of objects. The essential definition in most pica literature, however, includes culturally sanctioned non-food intake, especially if they are potentially harmful to health. This is probably reasonable when pica is being viewed as a mental illness. The Diagnostic and statistical manual of mental disorders, fifth edition (DSM-5) definition specifically excludes culturally sanctioned eating of non-nutritive substances. 1,2 One of the characteristics often emphasised is the strength of the craving, which has been likened to that for tobacco or alcohol. In medicine, the term generally refers to the persistent craving for, or eating of, non-food items. Pica is the Latin for magpie, a bird with a reputation for indiscriminate eating habits.
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