Which hormone peaks early to late morning and decreases by up to 30% during the day?

The hormone that peaks early to late morning and decreases during the day is growth hormone, not iron. Growth hormone is primarily secreted by the pituitary gland and exhibits a diurnal pattern of secretion, with levels typically rising during sleep and peaking early in the morning before gradually declining throughout the day.

Iron levels in the blood do not exhibit a defined diurnal rhythm like growth hormone. They can be influenced significantly by dietary intake and other factors but do not peak early in the morning nor show a specific decrease by 30% throughout the day.

Understanding the patterns of hormonal secretion, particularly growth hormone's diurnal variation, is crucial in clinical chemistry and pathology as it affects test interpretation and timing for accurate evaluations in various clinical conditions.