This study evaluates the cumulative incidence of Type 1 (insulin-dependent) diabetes mellitus in male army conscripts 0-18 (inclusive) years of age in the Netherlands (birth cohorts) over 10 years. Data from 2136 cases were retrieved from files of the conscript registry of the Royal Dutch Army. Ascertainment was sought by the capture-recapture method, achieving an average ascertainment rate of 89.7%. Poisson regression modelling was used to determine the change in incidence over time. A significant non-linear increase in the incidence of insulin-dependency in the birth cohorts of 1960-1970 was found. The cumulative incidences of the early birth cohorts 1.85/1000 (1960), 1.76/1000 (1961), 1.11/1000 (1962) were considerably lower than of the later birth cohorts 1.96/1000 (1968), 2.11/1000 (1969), 2.12/1000 (1970). Overall the risk of Type 1 diabetes increased on the average 4.4% with each annual birth cohort. Only for the 1962 birth cohort was a significant dip in the incidence observed. The results indicate a rapidly increasing incidence of diabetes in males in the Netherlands consistent with the concurrent rapid rise in Northern Europe, found in both sexes.

SUMMARY The relationship between sodium in drinking water and blood pressure was examined in 348 schoolchildren aged 7-7 to 11-7 years. They were born and living in three areas with different levels of sodium in the public drinking water. Sodium content of the water was either long-term low, long-term high, or short-term high. The three communities are closely comparable according to demographic characteristics. The mean values of systolic and diastolic blood pressure were higher in the high sodium areas. After adjustment for dissimilarities in distributions of weight, height, pulse rate, age, family history of hypertension, and time of blood pressure measurement, these differences remained constant, ranging from 1-8 to 4-0 mm Hg. Girls and boys showed essentially the same differences. Mean 24-hour sodium excretion was somewhat higher in the long-term low area; no differences were found in sodium-creatinine ratio. The regression coefficients between sodium excretion and blood pressure were not significant. The findings from this retrospective follow-up study support the hypothesis that sodium intake influences blood pressure. The association seems to be of a relatively short-term nature, as no differences in blood pressure levels were found between the long-term and short-term high areas.The role of high sodium intake in the pathogenesis of essential hypertension has been emphasised for a long time.' Epidemiologically this is mainly based on comparisons of the mean blood pressure levels of different populations with varying sodium intakes. Within populations, however, the results of blood pressure studies have been equivocal.26 Most of these investigations were cross-sectional, relating a casual blood pressure reading to an estimate of sodium intake at the same time. The major problems of this approach are that the estimates of sodium intake are generally very crude; furthermore, the time-course of the relation between dietary sodium and blood pressure is not taken into account. Therefore, follow-up studies are preferable because these can provide insight into the temporal aspects of the relationship under study.

This study suggests a sustained increase of type I diabetes in The Netherlands because the cumulative incidence studied previously in the 1960-1970 birth cohorts of male army conscripts 18 years of age was also found to rise. In contrast to Northern European countries, an increase in incidence for the age category 0-4 years could not be found.

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