Which hormone is highest in the morning due to diurnal variation?

• A. Growth hormone
• B. Cortisol
• C. Prolactin
• D. Iron

Answer: (B)

Diurnal variation means hormones follow a daily rhythm. Cortisol shows a clear circadian pattern with levels rising as you wake and peaking in the early morning—this cortisol awakening response helps mobilize glucose and energize you for the day. Growth hormone, by contrast, is released mainly in pulses during deep sleep, so its peak occurs overnight rather than in the morning. Prolactin does vary across the day, but it doesn’t have a dominant morning peak like cortisol. Iron isn’t a hormone at all, so it wouldn’t show a morning peak in this context. Therefore, cortisol is the hormone highest in the morning due to diurnal variation.