The Rise of Childhood Type 1 Diabetes in the 20th Century

Edwin A.M. Gale

Disclosures

Diabetes. 2002;51(12) 

In This Article

When Did the Increase Begin?

A steep rise in the incidence of childhood diabetes undoubtedly occurred in many populations over the latter part of the century. Backwards extrapolation of these trends often implies a zero incidence earlier in the century, which was clearly not the case. We therefore need to look for an upward inflection. The only previous attempt to track the incidence of type 1 diabetes across a century was made by Krolewski et al.[32], who concluded that a sharp upturn in the incidence of insulin-dependent diabetes had occurred in the U.S. around the mid-century. In Europe, the best evidence once again comes from Norway. The 1925-1954 Oslo survey was later extended to 1964, and an additional 3,368 patients were identified; 97% of the records were traced. After exclusion of nonresidents and patients diagnosed outside the city, this number fell to 2,859; 140 were aged under 20 years at diagnosis, and 90-95% of these were started at once on insulin. The incidence increased from a stable baseline of 4.1 cases/100,000/year to a new level of 8.4/100,000/year over the period 1955-1964[33]. This study was later reviewed by Joner and Søvik[34] in the light of their national survey of incidence from 1973 to 1977, and was considered sufficiently reliable to support their own conclusion that a secular change in incidence had taken place over the intervening period. Sequential studies have shown that the incidence of childhood diabetes in Norway increased until the last decade of the century[34,35,36], giving an S-shaped incidence curve over the 75 years for which information is available (Figure 2).

Incidence of diabetes in children under age 10 years in Norway, 1925-1995. Data from refs. 18,33-36.

Conscript studies lend support to the concept of an upturn in incidence around the middle of the last century. The first national conscript study was performed in Denmark, a country in which, since 1849, all males must appear before a conscript board from age 18 years. Diabetes certified by a physican automatically excludes military service, and the study not only tracked the medical records of almost all cases so recorded to verify insulin treatment, but also combed death certificates for individuals who had died before reaching that age. Successive male birth cohorts over the period 1949-1964 contained 638,718 individuals, of whom 1,652 appeared to have typical insulin-dependent diabetes by age 18 years, while another 30 had died with diabetes before that age. The cumulative rate of development of type 1 diabetes by age 20 years was 2.37/1,000 for the first eight birth cohorts and 2.90/1,000 for the last eight. Regression analysis demonstrated that the incidence of diabetes doubled over a 30-year period from the 1950s, apparently reaching a plateau in the late 1970s[37]. Therefore Denmark, like Norway, showed an upward inflection in incidence around the mid-century and an S-shaped incidence curve over its latter decades.

Three more conscript studies deserve mention. Males in Sardinia are called to medical examination before military service at the age of 20 years, and the prevalence of diabetes at that age has therefore been recorded for successive birth cohorts dating back to 1936. Diabetes was very rare in males born before 1945, but has risen in more or less linear fashion from the 1960s[38], although there are more recent indications of a plateau[2]. A conscript study in Switzerland examined files from 514,747 males from birth-year cohorts covering four periods between 1948 and 1972. The number of men with insulin-dependent diabetes by age 19 years rose by 62% over this interval[39]. A similar study in the Netherlands reported an average 4.4% increase in risk of type 1 diabetes for each annual cohort of 18-year-old conscripts over the period 1960-1970[40].

From 1965, drug treatment for diabetes has been free in Finland, provided that a certificate is submitted by a doctor. This has meant almost 100% ascertainment. Retrospective analysis of the period 1965-1984 showed a predominantly linear trend, equivalent to a 2.4% year-on-year increase[41]. Finland currently appears to differ from other Scandinavian countries and Sardinia in showing a continued linear increase in incidence[2].

In the U.K., childhood diabetes was considered so uncommon and demanding that ~10% of children were admitted to residential hostels in the 1940s. A 1949 survey of school medical officers identified 183 cases of diabetes, implying that 1 child in 4,300 under age 15 years was affected, although this was undoubtedly an underestimate[42]. Three national birth cohort studies initiated in 1946, 1958, and 1970 provide more reliable information. In the first cohort, only 1 child in 5,362 developed diabetes by age 11 years, as compared with 10/15,500 by age 11 years in 1958 and 18/13,823 by age 10 years in 1970. The corresponding prevalence rose linearly from 0.1 to 0.6 to 1.3/1,000, respectively (P < 0.05) (Figure 3). Although small, these prospective studies are of interest because all deaths under 11 years of age were scrutinized with particular care, and none were attributed to diabetes[43,44].

Cumulative incidence of diabetes from three U.K. birth cohorts. A progressive left shift in age of onset of the disease is shown. Redrawn from data in Kurtz et al.[44].

The best U.S. data for this period come from the Erie County Study. This was set up in 1962 to examine the incidence and prevalence of chronic diseases of childhood, and it involved identification of every affected child by retrospective examination of all case notes from hospitals serving a population of about 1 million over the period 1946-1961. Diabetes was estimated to affect 1/1,666 white children under age 16 years, with a total of 352 new cases over the period and five deaths. The incidence rose from 6.6/100,000/year in 1950-1952 to 7.4 in 1953-1955, 10.6 in 1956-1958, and 11.3 in 1959-1961[45]. A later analysis linking the Erie County data with a school survey in Michigan postulated a rising incidence of diabetes in the U.S.[46]. There is some doubt as to the quality of ascertainment in these studies, but adequately powered population-based studies are lacking for the period. For example, a study was performed in Rochester for the period 1945-1969, but the town contained only 26,500 inhabitants at the start of this survey[47]. The first diabetes registry was established in Allegheny County from 1965 onwards, with reported incidence rates ranging from 10.1 to 16.0/100,000/year according to sex and ethnic background. Although no change in incidence was reported over the period 1965-1976, the sample size was relatively small for time trend analysis, especially when subgroup analysis was undertaken[48].

This analysis therefore supports Krolewski in suggesting that the incidence of childhood diabetes was relatively low and stable until the mid-century, and showed an upturn from the 1950s onwards[32]. This appears to have developed around the same time in environments ranging from Northern Europe to the U.S. and Sardinia.

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