How many people live with T1D?
A disease can be counted in two ways. Incidence is the number of new cases arising over a period of time. Think of water running into a tub. Prevalence is the number of people living with the disease at a given time. That is the water level in the tub.
Type 1 diabetes (T1D) is lifelong, and its treatment is lifelong. A person stays in the living count until they die, while new cases keep joining it. So the level builds up over the years. This is why the number living with T1D is far larger than the number diagnosed in a single year.
In the United States, about 1 million people live with a diagnosis of T1D, and yearly incidence approaches 30,000 new cases. T1D is the less common form of diabetes. It accounts for about 5-10% of all cases of diabetes.
Who is diagnosed, and when?
A living total this large is built from people first diagnosed at different ages, so the next question is who they are and when the disease starts.
The disease is strongly associated with childhood. The peak age of diagnosis in children is about 10-14 years. It is often assumed that only children develop T1D, and that it affects only adolescence and early childhood. Both beliefs are misconceptions. Estimates place about 25-50% of cases in adults. Up to 40% of adults older than 30 with T1D may first be misdiagnosed with type 2 diabetes.
Is the number changing?
If childhood is where most diagnoses happen, the question is whether those counts are moving. They are. Annual incidence of T1D is rising by about 3-4% each year, and the rise is steepest in younger children. In European youth under 15 years of age, a 70% increase in prevalence was projected between 2005 and 2020. That figure was a trend projection.
What does living with it cost?
The burden of living with T1D reaches beyond blood glucose.
Control of T1D is hard in practice. Most patients do not keep their glucose well controlled. In one study of young children and adolescents, glycated hemoglobin (HbA1c) exceeded 9.5%, and HbA1c is the laboratory measure of average glucose over the previous months.
Beyond the metabolic consequences, the disease imposes a financial and an emotional burden on the person and their family.
Is it simply genetic?
Before asking what has changed, the common belief that T1D is purely genetic has to be set aside. It is widespread, but it is untrue.
Genetics are necessary for susceptibility to T1D. But genetics on their own do not determine who becomes ill. Environmental factors receive much attention for this reason.
Could genes explain the rise?
If genes are only part of the story, the next question is whether they can account for the rise. The rise in T1D is hard to explain by genetics alone, because genetic changes do not happen on the timescale of the rise. The increase points to environmental factors in the pathogenesis of T1D. A review attributes the rise in incidence to changes in the environment that have been only partly identified.
Where does the environment show itself?
A rise that genes cannot explain points to the environment, and the clearest evidence is geographic.
T1D incidence is close to six times higher in Finland than in neighbouring Russian Karelia. Yet the predisposing HLA-DQ genotypes, which raise susceptibility to T1D, are equally frequent in both places. Identical risk genes with very different disease rates leave the environment as the likely explanation.
The pattern also follows distance from the equator. T1D is more common in countries farther from it. The lowest incidence is near the tropics and the highest is in Northern Europe.
Which early-life exposures could be changing a child’s risk?