A key principle for physiological insulin delivery is to mimic the normal pattern of (3 cell function as closely as possible. Figure 1 shows insulin secretion in a healthy individual, measured every 10 minutes over a normal 24-hour period that included three standard meals—the top panel shows the actual data; the bottom panel is a stylized version used in this chapter as insulin programs are discussed. The multiple arrows in Figure 1A are large spikes of insulin secretion that occur every 1-3 hours and are called "ultradian oscillations"; the study from which the figure was taken investigated these oscillations (8). instead, view the figure for the 24-hour pattern of insulin secretion.
The following features of Figure 1 should be noted:
• There are three large peaks of insulin release that rise rapidly and then wane over 2-3 hours, corresponding to the meals. Also evident is a relatively constant secretion of insulin over the 24-hour period that is not food-related. The latter is critically important during the night and between meals to regulate glucose output from the liver; without it, hepatic glucose release increases markedly, resulting in high fasting and pre-meal blood glucose levels. These two components as applied to insulin treatment are termed "basal" (non-food-related) and "bolus" (meal-induced) insulin secretion.
• Quantitative insulin release for the meals is similar. This seems counterintuitive since caloric intake for supper is generally many-fold that for breakfast. The explanation is the "dawn phenomenon"—a lowering of tissue insulin sensitivity in the early morning hours because of the nighttime diurnal rise in Cortisol and growth hormone. Thus, we require more insulin secretion/injected per breakfast calorie than for supper. This underlies the confusion of many new insulin users about why the breakfast dose of rapid insulin typically equals or exceeds that for supper. It also explains why persons who use carbohydrate counting to determine meal insulin doses often use a lower ratio of grams of carbohydrate/insulin unit for breakfast than supper.
• Insulin secretion returns to the basal rate between meals. In other words, people are not designed to have much circulating insulin between meals. This has important implications for the common usage of breakfast-time NPH in the United States, which produces a nonphysiological sustained insulin effect from midmorning to late afternoon, necessitating between-meal snacks to prevent hypoglycemia.
patterns (when, what, how often) as well as other relevant factors (work shifts! alcohol) when designing an insulin regimen.
Was this article helpful?