Study strengths and limitations

Strengths of the study include the large sample of diabetic patients drawn from a general population and the fact that the sample was weighted to be nationally representative. However, patients volunteer for the panel from which respondents were drawn and may not be representative of all patients (e.g., they may be more adherent with their treatment regimens).

Limitations of the study include the fact that there was no objective measure of insulin use (e.g., pharmacy records). Moreover, while our measure of insulin omission was very specific (i.e., skipping injections that respondents knew they should take), it is possible that some respondents included injections they did not skip intentionally, but rather simply forgot to take. Respondents might also have included scheduled injections that were appropriately skipped because a meal was not eaten or blood glucose levels were very low. This could explain (at least in part) the association between following a healthy diet and fewer skipped injections. More disciplined eating behavior reduces meal skipping, which is an often-cited reason for skipping insulin injections. This is consistent with the fact that the relationship between our diet measure and insulin omission is present only among individuals with type 1 diabetes where closer matching of food and insulin is required.

Finally, our study probably underestimated the level of insulin nonadherence in this population because it did not capture instances in which patients took an injection but gave less than the amount of insulin they knew was needed for optimal glucose control.

Clinical implications

Our findings make clear that while most patients did not report regular omission of insulin injections, a substantial number did. Thus, our findings suggest that it is important to identify patients who omit insulin and to be aware of the potential risk factors identified here. Lack of personal resources (especially income) is one potential warning sign. Although much attention has been focused on insulin omission among adolescents with type 1 diabetes, our findings suggest that among adults, individuals with type 2 diabetes are at higher risk. Patients who are not adhering to other elements of the treatment regimen, especially diet, also may be at risk for insulin omission. For patients who report injection-related problems (interference with daily activities, injection pain, and embarrassment), providers should consider recommending strategies and tools for addressing these problems to prevent insulin omission. This may contribute to improved treatment adherence and consequent clinical outcomes.