Marjatta Karvonen

Worldwide increase in incidence of Type I diabetes – the analysis of the data on published incidence trends

Aims/hypothesis. Several reports on the incidence of Type I (insulin-dependent) diabetes mellitus have suggested that the incidence is increasing. The aim of this study was to find out whether the incidence is increasing globally or restricted to a selected populations only and to estimate the magnitude of the change in incidence.¶Methods. During 1960 to 1996 37 studies in 27 countries were carried out. To fulfil the inclusion criteria the study periods ranged from 8–32 years. The temporal trend was fitted by linear regression, with the logarithm of the age-standardized incidence as the dependent variable and the calendar year as the independent variable. Then, the regression coefficient ( × 100 %) is approximately the average relative increase in incidence per year (as percentage).¶Results. Results from the pooled data from all 37 populations showed that the overall increase in incidence was 3.0 % per year (95 % CI 2.6; 3.3, p = 0.0001). The statistically significant increase was found in 24 of 37 populations including all high incidence ( > 14.6 per 100 000 a year) populations. The relative increase was, however, steeper in the populations with a lower incidence. The correlation between logarithm of the incidence and the increase in incidence was r = –0.56, p = 0.0004.¶Conclusion/interpretation. The incidence of Type I diabetes is increasing worldwide both in low and high incidence populations. By the year 2010 the incidence will be 50 per 100 000 a year in Finland and also in many other populations it will exceed 30 per 100 000 a year. [Diabetologia (1999) 42: 1395–1403]

A review of the recent epidemiological data on the worldwide incidence of type 1 (insulin dependent) diabetes mellitus

SummaryNearly 70 registries from more than 40 countries have collected and published incidence data of childhood Type 1 (insulin-dependent) diabetes mellitus up to the end of the 1980s. The majority of incidence data comes from regions of high incidence i. e. from Europe and North American. All these published data facilitate the descriptive comparison of incidence and variation of the occurrence of Type 1 diabetes roughly throughout the northern hemisphere. The aim of this paper is to review and compare the most recent epidemiology data on the incidence of Type 1 diabetes among children under the age of 15 years. A clear difference in incidence appeared between northern and southern hemisphere with no countries below the equator having an incidence greater than 15.0 per 100,000. In contrast above the equator the disease is common. Between continents the variation in incidence showed that the lowest incidences were found in Asia, followed by Oceania (Australia and New Zealand), South and North America, and the highest rates were in Europe. The incidence varied from 0.6 per 100,000 in Korea and Mexico to 35.3 per 100,000 in Finland showing prominent worldwide variation in incidence of Type 1 diabetes. The largest intracontinental variation in incidence appeared in Europe, varying from the highest in Finland to the lowest (4.6 per 100,000)_in northern Greece. The highest incidence in the world was in northern Europe, but within the continent scale there were some striking exceptions from the overall level of incidence. In Iceland, the northern-most island nation in Europe, the incidence is only one-half of that in Norway and Sweden and one-third of that in Finland. In contrast, in Sardinia in southern Europe the Type 1 diabetes incidence is virtually the same as in Finland, three times higher than overall incidence in Europe. Large variation was also seen in small “pockets” of countries, particularly in the Baltic sea region. The worldwide variation in incidence reflects the distribution of ethnic populations and demonstrates the importance of the differential genetic susceptibility between populations.

Record-high incidence of Type I (insulin-dependent) diabetes mellitus in Finnish children

Aims/hypothesis. In Finland, the incidence of Type I (insulin-dependent) diabetes mellitus in children aged 14 years or under is the highest in the world and the trend in incidence has been increasing. Our aim was to determine the most recent trends in incidence and the age distribution at diagnosis of Type I diabetes. Methods. Data on the incidence of Type I diabetes in Finland nationwide were obtained from two sources: for the period 1965 to 1986 from the Central Drug Registry of the Social Insurance Institution and for the period 1987 to1996 from the prospective childhood Type I diabetes registry. The annual incidence was calculated per 100 000 people. The increase and the trend in incidence were estimated by fitting the linear regression model with the annual incidence data. Results. During 1987 to 1993 the incidence of Type I diabetes seemed to be rather stable at 36 per 100 000 per year. The incidence has continued to increase thereafter and reached 45 per 100 000 per year in 1996. The analysis of the long-term trend in incidence between 1965 and 1996 showed an absolute incidence increase of 0.67 per year on average being 3.4 % compared with the incidence in 1965. The increase from 1987 to 1996 was highest in very young children 1–4 years old at diagnosis. Conclusion/interpretation. The high incidence of Type I diabetes in Finnish children has thus far not levelled off but is increasing further. If the trend continues, the predicted incidence in Finland will be approximately 50 per 100 000 per year in the year 2010. [Diabetologia (1999) 42: 655–660]

Sex difference in the incidence of insulin-dependent diabetes mellitus: an analysis of the recent epidemiological data

Keywords: sex ratio; male-to-female ratio; insulin-dependent diabetes; incidence; epidemiology; geographical distribution

Seasonal variation of diagnosis of Type 1 diabetes mellitus in children worldwide

Aims  To determine if there is a worldwide seasonal pattern in the clinical onset of Type 1 diabetes.

Association between type 1 diabetes and Haemophilus influenzae type b vaccination: birth cohort study

Abstract Objectives: To determine the effect of Haemophilus influenzae type b vaccination and its timing on the risk of type 1 diabetes in Finnish children. Design: Cumulative incidence and relative risk of type 1 diabetes was compared among three birth cohorts of Finnish children: those born during the 24 months before the H influenzae type b vaccination trial, those in the trial cohort who were vaccinated at 3 months of age and later with a booster vaccine, and those in the trial cohort who were vaccinated at 24 months of age only. The probability of type 1 diabetes was estimated using regression analysis assuming that there were no losses to 10 year follow up and no competing risks. Setting: Finland (total population 5 million and annual birth rate 1.3%). Subjects: 128 936 children born from 1 October 1983 to 1 September 1985, and 116 352 children born from 1 October 1985 to 31 August 1987. Main outcome measures: Probability of type 1 diabetes among children vaccinated with H influenzae type b and non-vaccinated children. Results: No statistically significant difference was found at any time during the 10 year follow up in the risk of type 1 diabetes between the children born before the vaccination period and those vaccinated at the age of 24 months only (relative risk 1.01). The difference in the risk between the cohort vaccinated first at the age of 3 months and the cohort vaccinated at the age of 24 months only was not statistically significant either (1.06). Conclusion: It is unlikely that H influenzae type b vaccination or its timing cause type 1 diabetes in children.

Comparison of the Seasonal Pattern in the Clinical Onset of IDDM in Finland and Sardinia

OBJECTIVE To examine the seasonal pattern for the clinical onset of IDDM in Finland and Sardinia, two areas where the incidence of IDDM is the highest in the world, and to determine the effect of climate and temperature on the clinical onset of IDDM. RESEARCH DESIGN AND METHODS Analysis of seasonality for the diagnosis of IDDM was based on 1,405 cases in Finland and 425 cases in Sardinia diagnosed at ≤14 years of age from 1989 to 1992. The average annual incidence of IDDM was 36.4/100,000 in Finland and 34.4/100,000 in Sardinia. Seasonal patterns were estimated presenting the data as short Fourier series up to three harmonics together with a possible linear trend. Likelihood ratio tests and Akaikes information criterion were used to determine the number of harmonics necessary to model the seasonal pattern. Seasonal patterns in both countries were compared between sexes and between the three 5-year age-groups, each controlling for the others effect. RESULTS In both countries, a significant seasonal pattern during a calendar year was found for the sexes combined and for two age-groups (0–9 and 10–14 years). In Sardinia, two distinct cycles were found in the younger age-group, with a decreased incidence during May through August and an increased incidence during the autumn months. Two cycles were apparent in the older age-group, with the nadir occurring during June through September. In Finland, one cycle was found in the younger age-group, with a decreased incidence in June. In the older age-group, there were two distinct cycles, with a decreased incidence in June and in the September through December period. CONCLUSIONS Differences between Finland and Sardinia in the seasonal pattern for the incidence of newly diagnosed IDDM cannot be explained by differences in climate, temperature, a longer warm period in Sardinia, or other climatic phenomena. The results do not provide evidence in favor of a specific viral etiology of IDDM. It may be suggested that there are triggering events at certain times, but they are likely to be unspecinc. Nevertheless, why the incidence of IDDM in these two populations is equally high despite differences in climate, environment, and genetic background remains an unsolved question.

Increasing incidence of childhood-onset type I diabetes in 3 Baltic countries and Finland 1983-1998.

Abstract.Aims/hypothesis: We aimed to study the incidence of Type I diabetes in 4 countries, Estonia, Latvia, Lithuania and Finland, during 1983–1998, focusing on the two separate periods of 1983–1990 and 1991–1998. Methods: Population-based incidence data from nationwide diabetes registries were used. Crude and age-standardized incidence rates using the proportions of 39 %, 32 % and 29 % for 5-year age groups (0–4, 5–9 and 10–14 years) were calculated. Yearly incidence was evaluated and the means between the two periods compared. Results: Between 1983–1990 and 1991–1998 there was a statistically significant incidence increase in all 4 countries of Estonia, Lativia, Lithuania and Finland (relative risk 1.15, 95 %-Confidence interval 1.10–1.19) and as well as in the 3 Baltic states of Estonia, Latvia, Lithuania (relative risk 1.13, 95 %. Confidence interval 1.04–1.22). The crude incidence increased in Estonia from 10.1 (95 %-Confidence interval 8.9–11.4) to 12.3 (11.0–13.8), in Latvia from 6.6 (5.8–7.3) to 7.4 (6.6–8.2) and in Lithuania from 6.8 (6.2–7.5) to 7.8 (7.1–8.5). In Finland the incidence rose from 34.6 (33.3–36.0) in 1983–1990 to 40.8 (39.4–42.2) in 1991–1998. In children under 5 years of a age a statistically important increase was seen in Estonia and Finland. The highest incidence for a single year was recorded for all participating countries in the late 1990 s. The highest annual incidence rate of childhood onset Type I diabetes in the world ever known was recorded in Finland in 1998 with 48.5 cases per 100 000 person-years. Conclusion/hypothesis: The incidence of Type I diabetes has increased since 1983 in the three Baltic states as well as in Finland. Long-term monitoring is needed for a better detection in changes in incidence. [Diabetologia (2001) 44 [Suppl 3]: B 17–B 20]

The incidence of type 1 diabetes among children in Finland--rural-urban difference.

The aim of the study was to investigate the incidence of type 1 diabetes among children aged 14 years or under according to the level of urbanization of the place of residence of children at the time of diagnosis in Finland during 1987 to 1996. The analysis was carried out using a Bayesian approach and GIS. The incidence was the highest in the rural heartland areas while the increase in incidence was sharpest in urban areas. The level of urbanization seems to explain only a part of the spatial variation in the incidence in Finland. It is possible that some environmental risk factors for type 1 diabetes have been more prevalent in rural heartland areas than in the rest of the country. These factors might have increased in urban environments in Finland particularly during the first half of 1990s.

Incidence trends in childhood onset IDDM in four countries around the Baltic sea during 1983-1992

Summary We present secular trends of childhood onset insulin-dependent diabetes mellitus (IDDM) in Finland, Estonia, Latvia and Lithuania during the period of 1983–1992. Incidence data were obtained from the national IDDM registries. The average age-standardized incidence per 100 000/year was 35.0 in Finland, followed by 10.2 in Estonia, 7.1 in Lithuania and 6.5 in Latvia. A male excess in incidence was recorded in Finland (1.15) and Latvia (1.01). In all countries, the highest age-specific risk of IDDM was observed in the 11–13 year age range. The large difference in incidence between Finland and other Baltic countries was seen even in 1–2-year-old children. During the 10-year study period overall changes in incidence of IDDM were relatively small in these four countries. The incidence increased in Finland and Lithuania on average by 1 % and 1.4 % per year, respectively. A statistically significant increase was recorded only in 0–4 year old children in Finland, at 5.6 % per year. In Estonia, an 8.3 % increase in this age group, however, was not statistically significant. The different trends in the age-group specific incidence rates were confirmed in Finland. In conclusion, from 1983 to 1992 the incidence of childhood onset IDDM was increasing in Finland and Lithuania, while in Latvia and Estonia it was stable. There are still great differences in IDDM incidence between the countries around the Baltic Sea. [Diabetologia (1997) 40: 187–192]