田園都市住民の血清亜鉛値の実態と血清亜鉛値改善に向けての教育活動の影響について

In 2002, many zinc deficient patients visited our clinic in Kitamimaki (KI) Village, a rural area in Nagano prefecture. To understand why so many zinc deficiencies were found in the area, we devised a survey in 2003 (called Kitamimaki study) to determine the serum zinc (Zn) level of the residents. We found that the Zn level (75.8μg/dL) of the residents in Kitamimaki was 10μg/dL lower than in healthy Japanese people, though the reason for this was not clear. In 2004, Kitamimaki Village (KI) and the neighboring Tobu Town merged to become a larger city, called Tomi City. Tomi City is divided into five areas, two of which are rural (the KI and NE areas) and three of which are urban (the TA, KA and SH areas). This merger gave us the chance to survey more widely than we had in 2003. From July through October 2005, we conducted this study (called Tomi study) at the annual community-wide health examination for the city’s residents, In the study, we measured the Zn levels of 1773 participants, looking for differences in Zn levels in rural and urban residents, trying to ascertain whether Zn levels were lower in rural areas than in urban areas, and trying to understand why (or why not) this might occur.<br> Various studies indicate that Zn levels are affected by many factors, including age, gender, and the time of day samples are taken. In comparing the mean Zn levels and the appearance rates of loweved Zn level (under the lower limit of the standard zinc level - <65μg/dL) among the residents of each of the fire areas, we attempted to account for each of these factors, We compared the mean age and male/female ratio of each area, and used only the samples of 1017 participants whose blood was taken in the morning. The latter step was necessary because we needed to ensure that the conditions for subjects in each area matched those of subjects in other areas. In four of the five areas studied, there had been no previous interventions by local health authorities to improve Zn levels of the people residing there. Only for the residents of Kitamimaki, the subjects of our 2003 study, there had been such interventions. During the years between the Kitamimaki and Tomi studies, we tried various approaches to improve Zn levels in the Kitamimaki population, and consistently examined the efficacy of the efforts. Because of this, we did not compare the data from Kitamimaki with that of the other areas in the Tomi study.<br> [RESULTS and CONCLUSION] 1) Zn levels of males tended to be higher than those of females, and the levels also tended to be lower as individuals age. 2) The rate at which subjects’ Zn levels were under 65μg/dL was significantly higher (14.5%) in rural NE area than in urban TA and KA areas (8.0% and 7.5% respectively). 3) The mean Zn level (75.6μg/dL) of the residents in rural NE was significantly lower than those in the urban TA and KA areas (78.3 and 77.8μg/dL respectively). Even in urban areas, however, the mean Zn levels of the residents were lower than the mean level (86.9μg/dL) of healthy Japanese adults. 4) The low Zn level (75.8μg/dL) of KI residents in 2003, almost the same level (75.6μg/dL) of NE rural residents in Tomi study, improved after two-years of educational efforts. Campaigns including ‘Let’s eat a few more vegetables,’ ‘Take more soybean products,’ and ‘Lectures on zinc-rich foods’ helped raise Kitamimaki Zn levels.<br> We must continue to investigate the reasons why Zn levels of Tomi City residents, especially rural ones, are lower than elsewhere in Japan. We must pay more attention to interrelated, complex factors such as the amount of zinc in food, local soil composition, food additives, medicines, eating habits, and other factors affecting Zn levels in local populations.