Intermittent fasting does not influence the circadian pattern of melatonin when controlling for meals, light exposure and sleep schedules

Abstract

Introduction Melatonin is considered to be one of the best markers for circadian rhythm disruption, as individual melatonin profiles are highly reproducible and are less subject to masking factors than are other rhythm markers like core temperature and cortisol. Two previous studies have suggested a shift delay in the peak of melatonin during Ramadan. However, both studies did not control for food intake, light exposure, sleep schedule and social habits that accompany Ramadan. We hypothesize that if we control for the above confounders, Islamic intermittent fasting will not influence the circadian pattern of circulating melatonin. Therefore, we designed this study to assess the circadian pattern of melatonin during inside and outside Ramadan month when controlling for potential confounders. Materials and methods Eight healthy volunteers with a mean age of 26.6 ± 4.9 years and BMI of 23.7 ± 3.5 reported to the Sleep Disorders Center on four occasions: (1) adaptation; (2) 4 weeks before Ramadan while performing the Islamic fasting for 1 week (baseline fasting (BLF)); (3) 1 week before Ramadan (non-fasting baseline) (BL); (4) during the second week of Ramadan while fasting (Ramadan). Serum levels of melatonin were measured using ELISA five times at 2200, 0200, 0400, 0600 and 1100. Each participant received meals with fixed caloric intake and fixed proportions of carbohydrate, fat and protein based on their ideal body weight. Light exposure and sleep schedules were maintained the same during the participants’ stay in the SDC in the three study periods (BL, BLF and Ramadan). From 1800 until bedtime and during Suhur, light level was maintained at 50 lux. During sleep light level was 1 lux. Results During fasting (BLF and Ramadan), melatonin maintained the same peak level at 0200. The documented trough level was at 1100 in all studied periods (BL, BLF and Ramadan). This indicates that there were no significant changes in the circadian pattern of melatonin during fasting. Conclusion Under controlled conditions of light exposure, meals and sleep–wake schedules, Islamic intermittent fasting has no significant influence on the circadian pattern of melatonin. The changes reported in the previous studies could be related to the attendant lifestyle changes during Ramadan. Acknowledgements This project was supported by a grant from National Plan for Science and Technology (King Abdulaziz City for Science and Technology and King Saud University), Riyadh, Saudi Arabia.