to be iodine deficient. the study's authors suggested an investigation regarding "evidence-based recommendations for iodine supplementation". micronutrient deficiencies, including iodine deficiency, impair the development of intelligence. lacking iodine during human development causes a fall, in average, of 12 intelligence quotient (iq) points in china. a study of u.s. military data collected during the first and second world wars found that the introduction of salt iodization in the u.s. in the 1920s resulted in an increase in iq, by approximately one standard deviation, for the quarter of the u.s. population most deficient in iodine, explaining about "one decade's worth of the upward trend in iq" in the u.s. (i.e., the flynn effect). the same study documented "a large increase in thyroid-related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency". in iodine-deficient or mildly iodine-deficient areas of europe, iodine deficiency is frequent during pregnancy despite the widespread use of iodised salt, posing risks to the neurodevelopment of foetuses. in one study performed in a mildly iodine-deficient area, iodine deficiency was found to be present in more than half of breastfeeding women; in contrast, the majority of their newborns had iodine excess, mostly due to neonatal exposure to iodine-containing disinfectants. a 2014 meta-analysis found that iodine supplementation "improves some maternal thyroid indices and may benefit aspects of cognitive function in school-age children, even in marginally iodine-deficient areas". deficient populations in areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency gives rise to hypothyroidism, symptoms of which are extreme fatigue, goiter, mental slowing, depression, weight gain, and low basal body temperatures. iodine deficiency is the leading cause of preventable mental retardation, a result which occurs primarily when babies or small children are rendered hypothyroidic by a lack of the element. the addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but as of march 2006, iodine deficiency remained a serious public health problem in the developing world. iodine deficiency is also a problem in certain areas of europe. in germany it has been estimated to cause a billion dollars in health care costs per year. a modelling analysis suggests universal iodine supplementation for pregnant women in england may save £199 (2013 uk pounds) to the health service per pregnant woman and save £4476 per pregnant woman in societal costs. iodine deficiency was previously a common disease in norway, because the content of iodine in the drinking water was low. before 1950 goiter was a widespread disease caused by iodine deficiency. up to 80 per cent of the population were affected in inland areas. in the coastal communities, saltwater fish were an important part of the diet, and because of the presence of iodine in seawater, goiter was less common than in the inland districts. from the 1950s, norwegians started adding iodine to dairy cow feed. since milk was an essential part of the norwegian diet, the incidence of goiter decreased in the population.