Overview

• Researchers measured 236 expressed milk samples and found melatonin peaking at midnight and cortisol highest in the early morning.
• Authors recommend labeling stored milk by time of expression—morning, afternoon, evening—and feeding it at corresponding times.
• Samples were collected at 6 a.m., noon, 6 p.m., and midnight from participants over one or two days and analyzed for hormones and proteins.
• Oxytocin, IgA, and lactoferrin were largely stable across the day, with cortisol, IgA, and lactoferrin higher when infants were under one month old.
• The team notes a modest, not fully diverse sample and calls for larger studies that directly test infant responses to time‑matched versus unmatched feedings.