Epidemiology of type 1 diabetes

Type 1 diabetes may present at any age, but most typically presents in early life with a peak around the time of puberty. Its incidence varies 50–100-fold around the world, with the highest rates in northern Europe and in individuals of European extraction. Both sexes are equally affected in childhood, but men are more commonly affected in early adult life. The distinction between type 1 and type 2 diabetes becomes blurred in later life, and the true lifetime incidence of the condition is therefore unknown. A variant form known as latent autoimmune diabetes in adults (LADA) has been described. The incidence of childhood type 1 diabetes is rising rapidly in all populations, especially in the under 5-year-old age group, with a doubling time of less than 20 years in Europe. The increasing incidence of type 1 diabetes suggests a major environmental contribution, but the role of specific factors such as viruses remains controversial.

Incidence rates

Type 1 diabetes has historically been most prevalent in populations of European origin, but is becoming more frequent in other ethnic groups. Within Europe the highest rates of childhood diabetes are found in Scandinavia and north-west Europe, with an incidence range from 57.4 cases/100,000 per year in Finland to 3.9/100,000 in Macedonia for children aged 0–14 years.[1] Genetically related populations may differ in incidence: for example, type 1 diabetes is more common in Norwegians than in Icelanders of largely Norwegian descent, while Finnish children have a threefold risk compared with Estonians.[2] New cases of type 1 diabetes according to the IDF
New cases of type 1 diabetes according to the IDF
The incidence of type 1 diabetes remains relatively low in populations of non-European descent around the world, but many of these now report a rising incidence of the disease. Kuwait, for example, now has an incidence of 22.3/100,000. India and China have relatively low incidence rates for diabetes (4.2 and 0.6/100,000, respectively), but account for a high proportion of the world's children with type 1 diabetes because of their large populations. Statistics for the worldwide incidence of type 1 diabetes in children are available via the IDF Atlas.

Age-specific incidence

The incidence of type 1 diabetes reaches a peak at puberty, and declines rapidly thereafter. Classification of diabetes becomes more problematic in older age groups, and there are therefore no accurate estimates of incidence over the age of 40 years. A subgroup of individuals with develop diabetes in later life with clinical features of type 2 diabetes but test positive for GAD autoantibodies. As a group, these individuals are leaner and more likely to progress to insulin therapy, but there is controversy as to whether they represent a distinct subtype of diabetes or merely the tail-end of the distribution of type 1 diabetes within the population.

Sex

An international survey of sex ratios in children presenting under the age of 15 years noted a minor male excess in Europe and populations of European origin, while a female excess was noted in populations of African or Asian origin. High incidence populations are characterised by male excess, and low incidence populations by female excess.[3] In contrast, clear male preponderance has emerged from most studies of patients with type 1 diabetes diagnosed at 15–40 years. Adult type 1 diabetes therefore appears to differ from other common autoimmune diseases, which typically show a strong female excess, as does diabetes in the non-obese diabetic (NOD) mouse.[4]

Evidence of a rising incidence

Childhood-onset diabetes was a rare condition at the start of the 20th century. While many children may have died from undiagnosed diabetes, contemporary reports are consistent in suggesting that western populations had a low and relatively constant rate of the disease over the first half of the century at levels equivalent to those seen today in parts of southern Asia. From the middle of the 20th century, or soon after, a number of populations showed an upturn in incidence that has continued in more or less linear fashion to the present day.[5] The current overall rate of increase in Europe is about 3–4% per annum, and the most rapid increase is seen in the 0–5-year-old age group; the incidence in this age group is expected to double by 2020.[1] There are, however, important regional differences, with signs of a rapid increase in parts of eastern Europe[6] and of a levelling off in high-incidence countries such as Sweden.[7]

What explains the increase?

It has been suggested that the rising incidence of childhood diabetes might represent a left shift in age of onset rather than an absolute increase in the lifetime risk of the disease within a population, and this effect would be consistent with increased penetrance of susceptibility genes in the face of a more permissive environment.[8] Consistent with this, there is some evidence that the increase in the 0–14-year-old age group has been partially compensated by a decrease in young adults, so that the cumulative incidence by age 30 years remains unchanged,[9] [10] and there is also evidence that the proportion of children with the highest risk HLA haplotypes has declined over time.[11] This, and the speed of the increase within genetically stable populations, strongly suggests environmental influences, but is not convincingly explained by the specific factors currently under consideration.

References

  1. ^ Patterson CC et al. Incidence trends for childhood type 1 diabetes in Europe during 1989–2003 and predicted new cases 2005–20. Lancet 2009;373(9680):2027–33

  2. ^ Podar T et al. Increasing incidence of childhood-onset type 1 diabetes in three Baltic countries and Finland 1983-1998. Diabetologia 2001;44 Suppl B17–20

  3. ^ Karvonen M et al. Sex differences in the incidence of insulin-dependent diabetes an analysis of the recent epidemiological data. Diabet Metab Rev 1997;13:275–91

  4. ^ Gale EAM, Gillespie KM. Diabetes and gender. Diabetologia 2001;44:3–15

  5. ^ Gale EAM. The rise of childhood type 1 diabetes in the 20th century. Diabetes 2002;51:3353–61

  6. ^ Jarosz-Chobot P et al. Rapid increase in the incidence of type 1 diabetes in Polish children from 1989 to 2004, and predictions for 2010 to 2025. Diabetologia 2011;54:508–15

  7. ^ Berhan Y et al. Thirty years of prospective nationwide incidence of childhood type 1 diabetes. The accelerating increase by time tends to level off in Sweden. Diabetes 2011;60:577–81

  8. ^ Gale EAM. Spring harvest? Reflections on the rise in type 1 diabetes. Diabetologia 2005;48:2445–50

  9. ^ Weets I et al. The incidence of type 1 diabetes in the age group 0–39 years has not increased in Antwerp (Belgium) between 1989 and evidence for earlier disease manifestation. Diabetes Care 2002;25:840–46

  10. ^ Pundziute-Lycka A et al. Type 1 diabetes in the 0–34 years group in Sweden. Diabetologia 2002;45:783–91

  11. ^ Hermann R et al. Temporal changes in the frequencies of HLA genotypes in type 1 diabetes – indication of an increased environmental pressure? Diabetologia 2003;46:420–25

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