Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers .

1. Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers. By: C. Simon, L. Weibel, and G. Brandenberger Presented by: Greg Lendzion

2. Study Purpose “Define the ultradian and the circadian rhytmicities of insulin secretion rate and plasma glucose in night workers … and to evaluate their (night workers) degree of adaptation to the nocturnal schedule.” Taken from Article

3. Types of Hormone Rhythms • Circadian Rhythms • Impulses of hormones that have a 24 hour cycle pattern. • Ultradian Rhythms • Impulses of hormones that have a cycle pattern less than 24 hours.

4. Previously Established effects of daytime-sleeping on hormone release • Circadian Rhythms partially adapt to day-sleeping when compared to night-sleeping • Alteration in normal growth hormone secretion • Alteration in normal circadian rhythms of melatonin, cortisol, and TSH

5. Subjects • Eight (24-35 yr old) Regular night workers • Eight (23-30 yr old) Day-active subjects. • All Subjects: • Good Health • High Work Satisfaction • No complaints of fatigue, sleep disturbance or mood alteration • Normal body weight • No personal or family history of endocrinological disorders.

6. Measurements of the Study • Sleep quantity and quality • Glucose Levels • Insulin secretion rate (ISR)

7. Sleep Quality and Quantity • Sleep times determined by researchers. • 8 hours in a dark, air-conditioned room. • Sleep was quantified by various sleep recording machines.

8. Glucose Levels • Given continuous enteral nutrition to avoid eating and fasting • Acquired by 10-min. blood sampling continuously for 24 hours. • Measured in grams/Liter

9. Insulin Secretion Rate • Calculation based on plasma C-peptide levels • Fluctuates with ultradian oscillations every 50 to 150 minutes. • Closely linked with plasma glucose levels • Irregular insulin secretion rate oscillations have been linked to non-insulin diabetes and minimal impaired glucose intolerance.

10. Subjects sleeping data throughout the study • Table 1: Comparison of sleep parameters Taken from: Article in review.

11. Mean 24-h Glucose and ISR Profiles • Figure 1 from Article

12. Data from Mean 24-h glucose and ISR Profiles • Adapted from Article

13. Night-Sleep Glucose and ISR increased at beginning, plateau at middle, and decreased at the end of sleep Glucose and ISR were significantly higher during sleep periods than when awake Day-Sleep Glucose levels remained relatively the same with no noticeable peaks or troughs ISR levels showed a peak at the middle of sleep period, however the amplitude was smaller than during night sleeping Day-Active Subjects

14. Night Working Subjects • Glucose and ISR peaks were reflective of the day-active with night sleeping pattern. • Mean plasma glucose and ISR were higher during the wake periods than the Day-active subjects

15. Ultradian Glucose and ISR Rhythmicity Figure 2 from Article

16. Adapted from Article

17. Ultradian Glucose and ISR Rhythmicity Results • No significant difference seen in the oscillation count, duration, and interpulse interval between the three groups • Overall, no significant difference of amplitude noted over the entire 24 hour time period for the three groups

18. Mean Glucose and ISR Oscillation Amplitudes • Legend: • Mean Amplitude of glucose and ISR oscillations in four hour periods • Black bars indicate sleep periods. • Figure 4 from Article

19. Day-Active Subjects Night Sleep Consistent with peak level of glucose at the beginning of sleep and a peak ISR level at the end of sleep Day Sleep Glucose levels drop lower after sleeping when compared to night sleeping ISR Levels remain elevated immediately after sleeping when compared to night sleeping Night Worker Subjects Glucose begins to elevate four hours prior to sleeping when compared to the day-active night sleeper’s levels ISR levels are slightly elevated immediately after sleeping when compared to the day-active night sleeper’s levels Analysis of Mean Glucose and ISR Oscillation Amplitudes

20. Overall Conclusion • Plasma glucose and ISR levels are influenced by circadian rhythms. • Night Workers only partially adapt their glucose and ISR levels to their sleeping schedule. • Night Workers have a higher risk of glucose intolerance and detrimental effects of elevated glucose levels.

21. Possible Future Studies • Need to study alterations in diet and exercise in night workers and it’s effect on glucose and ISR levels • Need to use a larger subject base to substantiate or refute this studies findings • Need to examine atypical subjects (smokers, obese, etc.)

22. References • Simon, C., Wiebel, L., Brandenberger, G.; Twenty-four-hour rhythms of plasma glucose and insulin secretion rate in regular night workers. American Journal of Physiology – Endocrinology and Metabolism. 278:E413-E420, 2000.