Normal Patterns of Insulin Secretion Throughout the Day in Humans
In normal physiology, insulin is secreted in a pulsatile but continuous pattern throughout a 24-hour period, with basal insulin secretion occurring at a rate of 0.5-1 units per hour (representing 48-52% of total daily insulin production) and postprandial insulin secretion increasing 3-10 times over a 4-hour period after meals. 1
Basal Insulin Secretion
Basal insulin is continuously produced by the pancreas between meals and during fasting states at a nearly constant rate. This continuous secretion serves critical metabolic functions:
- Restrains glucose release from the liver
- Limits free fatty acid release from adipose tissue
- Prevents hyperglycemia and ketosis in the fasting state 2
- Represents approximately half of the total daily insulin production 1
Postprandial Insulin Secretion
After meals, insulin secretion follows a distinct biphasic pattern:
- First phase: Rapid rise within 3-5 minutes, lasting up to 10 minutes 1
- Second phase: Slower and extended release lasting 60-120 minutes 1
- Overall postprandial insulin levels remain elevated for about 4 hours before returning to basal rates 1
- Postprandial insulin secretion increases 3-10 times above basal levels 1
Circadian Rhythm of Insulin Secretion
There is a clear circadian (approximately 24-hour) rhythm to insulin secretion:
- Insulin secretion rates increase from a nadir between midnight and 6 AM
- Peak insulin secretion occurs between noon and 6 PM 3
- This pattern is opposite to melatonin levels, which peak when insulin secretion is lowest 3
- Glucose tolerance and insulin responses to glucose are higher in the morning than at night 3
Meal-Related Patterns
Interestingly, there are differences in insulin response depending on meal timing:
- Postprandial glucose excursion is significantly lower at breakfast than at lunch and dinner
- β-cell responsivity to glucose and disposition index are higher at breakfast
- Hepatic insulin extraction is lower at breakfast than dinner 4
Timing of Postprandial Peaks
- Mean peak time after meals is approximately 72±23 minutes
- 80% of postprandial glucose peaks occur within 90 minutes after starting a meal 5
- Peak times are similar after breakfast, lunch, and dinner 5
Alterations in Disease States
While not the focus of your question, it's worth noting how these normal patterns change in pathological states:
Obesity: Maintains the pattern of basal and postprandial insulin secretion but at 5-6 times higher rates, with insulin levels remaining elevated after meals and not fully returning to baseline 1
Type 1 diabetes: Typically lacks clinically meaningful insulin secretion 1
Type 2 diabetes: Shows a blunted glucose-mediated insulin secretion pulse (approximately 70% of normal) with loss of first-phase insulin secretion 1
Prediabetes: First-phase insulin secretion is already lost 1
Understanding these normal patterns of insulin secretion is crucial for designing optimal insulin replacement strategies in diabetes management and for the development of artificial pancreas systems that aim to mimic physiological insulin patterns.