What Does "Basal" Mean in Insulin Therapy?
Basal insulin refers to the background, long-acting insulin that suppresses hepatic glucose production and controls blood sugar levels overnight and between meals, independent of food intake. This is fundamentally different from prandial (mealtime) insulin, which covers glucose excursions from eating 1.
Physiologic Basis
The principal action of basal insulin is to restrain hepatic glucose production and limit hyperglycemia overnight and between meals 1. In healthy individuals, the pancreas secretes a sustained, low level of insulin continuously throughout the 24-hour period, which prevents the liver from releasing excessive glucose 2, 3. This basal secretion is distinct from the large bursts of insulin released after meals (bolus or prandial insulin) that decay over 2-3 hours 2, 3.
Clinical Application
Basal insulin provides continuous background coverage to maintain fasting glucose control, typically administered as once-daily long-acting insulin analogs such as glargine, detemir, or degludec 1.
In type 2 diabetes, basal insulin alone is the most convenient initial insulin regimen and can be added to metformin and other oral agents, with starting doses of 0.1-0.2 units/kg/day 1.
In type 1 diabetes, basal insulin typically represents 40-60% of the total daily insulin dose, with the remainder provided as prandial insulin divided among meals 4, 5.
Key Distinction from Prandial Insulin
Basal insulin does NOT cover meals—it only addresses fasting and between-meal glucose 1. When patients require coverage for postprandial (after-meal) glucose excursions, rapid-acting prandial insulin must be added separately 1, 6. This is a critical concept: escalating basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage leads to "overbasalization" with increased hypoglycemia risk and suboptimal control 1, 4.