Diurnal variation of insulin clearance and sensitivity in normal man.
Level 2 - randomized trial
Randomized trial with within-subject morning versus evening crossover comparisons
What was done
Sixteen healthy volunteers were randomized into two groups to receive either a low-dose (8 mU/M2/min) or high-dose (40 mU/M2/min) insulin infusion clamp study. Each participant received their assigned clamp twice: once in the morning (0800-1000) and once in the evening (1800-2000), each preceded by a 9-hour fast. Diurnal insulin clearance and insulin sensitivity (judged by glucose infusion rate divided by ambient serum free insulin level, M/FI ratio) were evaluated.
What was found
Serum insulin clearance showed diurnal variation with higher values in the evening in both the high-dose group (AM: 791 +/- 54 ml/min/M2 vs PM: 947 +/- 53 ml/min/M2, p < 0.01) and the low-dose group (AM: 411 +/- 32 ml/min/M2 vs PM: 716 +/- 87 ml/min/M2, p < 0.001). Diurnal variation in insulin sensitivity was observed only in the low-dose group, being significantly higher in the morning (AM: 14.6 +/- 2.4 vs PM: 10.5 +/- 1.1, p < 0.05).
Why it matters
This study demonstrates that healthy human insulin clearance is higher in the evening regardless of dose, whereas peripheral insulin sensitivity is enhanced in the morning under physiological insulin levels.
Limits
The sample size is very small (16 subjects split into two dose groups). Participant demographics such as age and sex are not reported in the abstract. Findings reflect controlled 9-hour fasting clamp conditions and may not directly extrapolate to normal meal ingestion or individuals with metabolic disease.
Cited by
- supports Humans are most insulin-sensitive during the early morning hours and most insulin-insensitive in the evening.