Why does urine turn yellow when drinking less water?

Maybe everyone has noticed that sometimes when you are busy, you forget to drink water, and the urine turns yellow. Then you quickly drink water and it becomes normal. In addition, our morning urine is also yellower than that during the day. Why does urine turn yellow? What is the reason?

In fact, this is a simple concentration problem. The color of urine is mainly caused by the change in the concentration of metabolites in urine. Let's talk about it below.

01 Why does urine turn yellow?

If the amount of metabolic waste in the human body is X under normal circumstances, the amount of urine excreted is V, and the concentration is c, then the urine concentration is c=X/V.

It can be seen that the concentration of metabolites in urine is inversely proportional to the urine volume. Therefore, the less urine volume, the higher the concentration and the darker the color. (Here, urine volume can be understood as the average urine volume)

So someone will definitely ask, it is obviously the amount of water you drink. Yes, under normal circumstances , the total amount of urine a person excretes is directly proportional to the total amount of water he or she consumes .

Otherwise, the body's homeostatic balance ( physical and chemical properties and chemical composition, such as electrolytes ) will be disrupted. Drinking more and excreting less will cause edema, while drinking less and excreting more will cause dehydration.

It means that the normal state is an ideal state, which means that the body is stable and the intake and excretion are both stable. For example, if you eat salty food or sweat due to high temperature, it does not belong to this setting.

02 Let’s talk about urine

Urine is the final metabolic product produced by blood filtration through the glomerulus, reabsorption and excretion by the renal tubules and collecting ducts.

The composition and properties of urine can reflect the body's metabolic status and are affected by the functional status of various systems of the body. Normal newly excreted urine is mostly transparent, light yellow or colorless, mainly because it contains urochrome; secondly, it is also affected by urobilin, urobilinogen and porphyrin.

So what factors affect urine color?

1. Water intake

2. Food: For example, taking too much carotene will deepen

3. Metabolism: For example, too much phosphate can cause urine to turn white

4. Pathology: In pathological conditions, such as obstructive jaundice and hepatocellular jaundice, the urine contains a large amount of direct bilirubin, so it is dark yellow. Therefore, the change in urine color can assist in the diagnosis of the disease and is also an important indicator in judging the prognosis and efficacy.

So, don’t underestimate the color of urine, it is also a barometer of our body.

Ding Liping et al., Study on the relationship between urine color and urine amylase determination, Modern Laboratory Medicine, Vol. 17, No. 2, May 2002