I know a lot about diabetes and working with my insulin. But recently a friend sent me an article, “Rapid-Acting Insulin, Timing It Just Right”, written by well-noted certified diabetes educator and registered dietician, Hope Warshaw. It helped confirm some of what I know and helped clarify some of what I didn’t know about timing insulin with your meals. Here are some of the article’s highlights.

Warshaw points out that even when you think you’re doing everything right with your diabetes care regimen, your blood glucose levels can seem hard to control. One potential source of difficulty is how you time your injections of rapid-acting insulin with respect to meals.

Most diabetes experts recommend taking meal-time insulins (Humalog, Novolog and Apidra) within 15 minutes of starting a meal. This advice is based on the belief that rapid-acting insulin is absorbed quickly and begins lowering blood glucose quickly. However, this may not be true for everyone. 

Howard Wolpert, M.D., editor of the book Smart Pumping and Senior Physician and Director of the Insulin Pump Program at Joslin Diabetes Center, cautions against blind-faith acceptance of insulin action curves or standard advice about when insulin works, noting that insulin can show “a lot of variability…between individuals and even within the same person from day to day.” The time ranges given for an insulin to reach its peak action are averages, so they may not fit everyone or every situation. You may find through blood glucose monitoring and experience that rapid-acting insulin typically reaches peak effectiveness within 45–90 minutes or possibly sooner or later. In general, people with normal stomach emptying can expect some glucose from the carbohydrate they’ve eaten to start raising their blood glucose level within minutes of starting to eat. Blood glucose level tends to peak about one to two hours after the start of a meal and gradually drops over the next three hours.

If rapid-acting insulin always started working almost immediately and peaked one to two hours later, injecting it anytime within 15 minutes of starting to eat would work well. But newer observations suggest that rapid-acting insulin doesn’t get absorbed and start working that quickly in all people. John Walsh, P.A., C.D.E., coauthor of the book Using Insulin, for example, believes the maximum blood-glucose-lowering effect of rapid-acting insulin may occur much closer to two hours after an injection rather than 45–90 minutes. If this is the case, the optimal time to take rapid-acting insulin is 10 to 15 minutes before eating rather than with the first bite or 15 minutes after starting a meal. Walsh’s belief is based on research suggesting that insulin may be measurable in the bloodstream before it begins actively lowering blood glucose.

Some other factors that may cause insulin action to differ from the action curve given in product literature or to vary from person to person include thickness of the subcutaneous fatty layer at an injection site, temperature, blood flow, exercise, and dose size. (The choice of injection site—abdomen, thigh, arm, buttock—does not seem to affect the absorption rate of rapid-acting insulin as it does for slower-acting insulins.) Injecting into areas that have more subcutaneous fat tends to slow insulin absorption. Widened blood vessels (caused by higher temperatures or exercise) allow insulin to be absorbed more quickly; constricted blood vessels (caused by colder temperatures or smoking) can cause slower absorption. Large doses of insulin may also be absorbed somewhat more slowly than smaller doses.

Thank you Ms. Warshaw. Since this is a lengthy article there’ll be more from Hope’s article over the next few posts.