Why is your first morning urine look brownish red?

First morning urine is typically more concentrated than urine produced later in the day as a result of the body conserving water overnight to prevent dehydration during sleep. As the kidneys perform their function of filtering waste products and excess water from the blood to produce urine, they also reabsorb essential nutrients and water back into the body. Overnight, however, there is a prolonged period without fluid intake, causing increased reabsorption of water from the urine. As a result, the morning urine becomes more concentrated, displaying a darker amber or reddish hue.

The reddish-brown color of the first morning urine can be attributed to the presence of urobilin, a pigment produced during the breakdown of hemoglobin, the oxygen-carrying protein in red blood cells. As old red blood cells are broken down, their hemoglobin is processed by the liver to form bilirubin, a yellow pigment. Bilirubin is then excreted from the body, with a portion of it going to the intestines and being converted into urobilin by bacteria. Some of the urobilin is then reabsorbed into the bloodstream and filtered by the kidneys into the urine.

During the night, due to reduced fluid intake, urine production is decreased, and the concentration of urobilin in the urine increases, giving it a darker reddish-brown appearance. As hydration improves throughout the day with increased fluid intake, the urine color gradually becomes lighter.

It's worth noting that while reddish-brown urine is typically caused by concentrated urine, it can sometimes be a sign of other medical conditions, such as dehydration, excessive sweating, or certain liver or kidney disorders. In these cases, the urine may also present with additional symptoms or abnormalities, and consulting a healthcare professional for proper evaluation would be advisable.