Among the diurnal variation list, which hormone is highest in the morning?

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

Answer: (A)

Cortisol has the strongest diurnal rhythm, peaking in the early morning just after waking. This morning surge, known as the cortisol awakening response, helps supply energy for daily activities and is driven by hypothalamic CRH triggering pituitary ACTH and then adrenal cortisol release. After the morning peak, cortisol gradually declines throughout the day. Growth hormone is released mainly in pulses during sleep (especially in the early night), so its highest levels are not in the morning. Prolactin rises and varies with sleep and other stimuli but does not show a pronounced morning peak. TSH tends to have its own nocturnal pattern, not a clear morning maximum. Thus cortisol is highest in the morning.