Type 1 diabetes (T1D) is an autoimmune disease, often diagnosed early in life, characterized by the destruction of the insulin-secreting β cells in the pancreas. As a consequence, patients become insulin-dependent and must follow a rigid, daily regimen of exogenous insulin replacement. In contrast, type 2 diabetes (T2D) is typically a disease of adulthood (although more cases are now being seen earlier in life), where a relative insulin deficiency arises due to insulin resistance and abnormal pancreatic β cell function 
. The American Diabetes Association (ADA) estimates that there are 17.9 million individuals diagnosed with diabetes in the U.S. 
, with 5 to 10 percent representing those with T1D 
. Epidemiologic studies suggest that the incidence rate of T1D has been growing worldwide, especially amongst young children 
With the increasing focus on the T2D epidemic, the impact of T1D in this country is often overlooked, particularly from an economic perspective. Many cost-of-illness (COI) studies have been performed on diabetes, but most combine the costs for T1D and T2D over just one year. The Agency for Health Research Quality (AHRQ), using the Medical Expenditures Panel Survey (MEPS), a nationally representative data set 
, reports that $34 billion in health expenditures were related to diabetes in 2005 
. A frequently quoted study by the ADA improves upon this number by using the attributable risk methodology to calculate the portion of expenditures on related comorbidities that is due to diabetes 
. The researchers also include other non-medical costs (i.e. lost work days, bed days, and increased mortality), which are important factors in the cost of diabetes. The study finds that diabetes is responsible for $92 billion in medical expenditures and $40 billion in indirect costs in 2002. An ADA update finds that in 2007 the total cost of diabetes had increased to $174 billion ($155 billion in 2002 dollars), the increase in costs due to increased populations of diabetics 
. Another recent study projects that the costs of the diabetes epidemic will have risen to $336 billion (2007 dollars) by 2034 as the diabetes patient population exceeds 44 million 
These studies do not break down diabetes costs by type in their estimates. Rather, they attempt to apply the proportion of patients with type 1 to obtain the fraction of costs attributed to type 1, an assumption that does not account for the distinct nature and differing disease progressions of the two forms of the disease. Furthermore, there is wide variation in results among the cost studies. For example, a study by the Milken Institute calculates combined T1D and T2D indirect costs to be over $105 billion in 2003 
. The discrepancy is due to the inclusion of differing cost components and varying underlying methodologies. Studies that do specifically examine the T1D population concentrate on children, are not nationally representative, are not U.S. based, or only look at medical expenditures 
. One recent exception by Dall et al. 
, using medical claims data to identify T1D patients, compares the annual costs of T1D with T2D in the U.S. and finds the costs of T1D to be disproportional to the number of T1D patients compared with the number of T2D patients.
Patients with T1D typically suffer from the disease for a longer period of time. Regular maintenance of T1D requires daily insulin shots and constant monitoring, representing a significant lifelong cost and time requirement. For T1D, these long-term effects are likely to spill over to other aspects of their lives with resulting economic impacts particularly in indirect costs. Milton et al. 
compile and review studies in the literature addressing the social consequences of T1D. The evidence is mixed. They find that children with T1D are more likely to miss school and that the employment outcomes are worse, but school performance and educational attainment remain unaffected. Providing lifetime cost estimates, as well as annual costs, would allow comparison among diseases that take into account the full economic impact of chronic diseases and facilitate discussions of benefits of possible cures.
To address these deficiencies and provide a comprehensive first step in identifying the annual and lifetime costs of T1D, this study was designed to estimate the direct medical expenditures and indirect costs associated with T1D in the U.S. Together with more traditional biomedical research into the causes and treatments of T1D, this study allows for a comprehensive understanding of the costs and benefits associated with the disease. Doctors, patients, researchers, policy makers, and drug developers can use these results to more fully understand the impact of T1D on individuals and society.
In this paper, we present the results of this analysis that show, as might be expected given the different disease pathologies that underlie the forms of diabetes, that the cost breakdown in T1D is different than T2D, with indirect costs being disproportionately larger for T1D. Furthermore, we show that over a lifetime, the economic costs of T1D are in excess of $10 billion for a new yearly cohort of approximately 30,000 patients.