Level of evidence:
Frequently asked questions about the body clock
What time of day is cortisol highest?
Within 30 to 45 minutes after waking up: it rises by about 50% compared with the moment of waking (Fries, 2009). It then falls throughout the day and reaches its lowest point around midnight.
What time does melatonin start to rise?
About 2 hours before your usual bedtime, as long as you are in dim light. Bright light in the evening delays this rise (Burgess, 2003).
Why do you get tired in the early afternoon?
Partly because of the body clock: a dip in alertness comes in the middle of the afternoon, even without lunch. A meal rich in sugars makes it stronger (Monk, 2005).
Why are you hungrier in the evening than in the morning?
Appetite also follows the body clock: in a study where meals and sleep were spread across all hours of the day, hunger was lowest around 8 a.m. and highest around 8 p.m. (Scheer, 2013).