Table 2.

A summary of the studies that objectively assessed changes in melatonin during diurnal intermittent fasting for Ramadan

Study	Study population	Study design	Assessment tool	Study setting	Findings	Study details
Bogdan et al27	10 healthy male volunteers (age: 32–40 years) Location: France	Case crossover study with repeated measures	Blood samples were obtained every 4 hours, omitting the 02:00 time point, before and on the 23rd day of Ramadan	Free-living environment Controlled for meal timing and composition Did not control for light exposure, sleep schedule, or social habits that accompany Ramadan	A decreased and delayed night peak and a flattened slope of serum melatonin concentration in Ramadan	Volunteers slept 1 hour less during Ramadan than before Ramadan Melatonin concentrations were not measured late at night, which fails to address the possibility of a late peak in melatonin concentration
BaHammam et al30	8 healthy young adults (age: 31.8±2 years) Location: Saudi Arabia	Case crossover study with repeated measures	Saliva samples were collected at three time points over a 24-hour period (08:00, 16:00, and 00:00) before and on the 7th and 21st days of Ramadan	In-laboratory monitoring Controlled for meal timing and composition Controlled for sleep duration Did not control for light exposure or social habits that accompany Ramadan	A significant decrease in melatonin concentrations at 00:00 and 16:00 during Ramadan Melatonin profiles continued to show the same trend during Ramadan, but with a flatter slope	Melatonin concentrations were not measured late at night, which fails to address the possibility of a late peak in melatonin concentration
Almeneessier et al28	8 healthy young adults (age: 26.6±4.9 years) Location: Saudi Arabia	Case crossover study with repeated measures	Blood samples were collected at 22:00, 02:00, 04:00, 06:00, and 11:00 before Ramadan and while performing fasting outside Ramadan month and on the second week of Ramadan	In-laboratory monitoring Controlled for light exposure, sleep schedule, sleep duration, energy expenditure, and meal composition	Intermittent fasting during Ramadan has no significant effect on the circadian pattern of melatonin	Assessed melatonin level when volunteers were fasting outside Ramadan month to control for lifestyle changes that accompany Ramadan