Which water-soluble vitamins are excreted in urine?

January 1, 2026 •

4 min read

Over 90% of excess water-soluble vitamins that are absorbed by the body are eventually excreted through the urine. This process is the body's natural way of regulating nutrients, with most of the B-complex vitamins and vitamin C being the primary ones excreted when not needed.

Quick Summary

Excess water-soluble vitamins, including most B vitamins and vitamin C, are flushed from the body via the kidneys and into urine because they are not stored. A consistent daily intake is required to maintain adequate levels and prevent deficiencies.

Key Points

Excretion of Excess: All water-soluble vitamins, including vitamin C and most B vitamins, are excreted in the urine when the body has an excess.
Limited Storage: Unlike fat-soluble vitamins, water-soluble vitamins are not stored in large quantities in the body, requiring consistent daily intake.
The Yellow Urine Effect: Excess Riboflavin (B2) is particularly noticeable as it can cause urine to turn a bright yellow color.
Vitamin B12 is the Exception: Unlike other B vitamins, Vitamin B12 is stored in the liver and can be retained for years, so it is not rapidly excreted.
Dietary Importance: Because they are not stored, maintaining health depends on a regular, balanced diet rich in water-soluble vitamins.
Cooking and Stability: Water-soluble vitamins are sensitive to heat and can be washed out during cooking, which means food preparation methods can impact nutrient levels.

The Fundamental Difference: Water-Soluble vs. Fat-Soluble Vitamins

Vitamins are vital organic compounds that the body needs in small amounts to function properly. They are categorized into two primary groups based on how they are absorbed and stored: water-soluble and fat-soluble. Fat-soluble vitamins—A, D, E, and K—dissolve in fat and are stored in the body's fatty tissues and liver, allowing for reserves over time. In contrast, water-soluble vitamins dissolve in water and are absorbed directly into the bloodstream. Because they can travel freely in the body's watery environments, any excess amounts that the body doesn't need are readily filtered out by the kidneys and expelled in the urine, necessitating regular dietary intake.

A Closer Look at the Water-Soluble Vitamins Excreted in Urine

The water-soluble group includes vitamin C and the eight B-complex vitamins. All are susceptible to urinary excretion, though the rate and amount can vary. Here is a breakdown of the specific vitamins that are primarily eliminated this way.

Vitamin C (Ascorbic Acid)

Vitamin C, or ascorbic acid, is a powerful antioxidant essential for tissue growth and repair, iron absorption, and immune function. The body has a finite capacity to absorb and utilize vitamin C from food or supplements. Once the body's tissues are saturated, any additional intake is cleared by the kidneys. This is why extremely high doses of vitamin C, while often marketed as a boost for immunity, simply lead to more of the vitamin being excreted rather than stored.

The B-Complex Vitamins

The B-complex group consists of eight different vitamins, each playing a crucial role in cellular metabolism and energy production. With one notable exception, the B vitamins are not stored in significant quantities and are excreted when in excess.

Thiamin (B1): Essential for converting nutrients into energy. Excess thiamin is eliminated in the urine.
Riboflavin (B2): Involved in energy production and acts as an antioxidant. It is well-known for being excreted in large amounts, which is why multivitamins or B-complex supplements can cause urine to turn a harmless, bright, almost neon yellow.
Niacin (B3): Functions as a coenzyme in energy metabolism. Excess intake is methylated and excreted in the urine.
Pantothenic Acid (B5): A component of coenzyme A, which is central to metabolism. Excess amounts are excreted.
Pyridoxine (B6): Important for amino acid metabolism and neurotransmitter synthesis. Metabolites are excreted via the kidneys.
Biotin (B7): A coenzyme for carboxylases involved in various metabolic processes. Excess biotin is eliminated in the urine.
Folate (Folic Acid/B9): Crucial for DNA synthesis and red blood cell formation. While the liver stores some folate, excess is excreted.
Cobalamin (B12): This is the exception among the water-soluble vitamins. The body can store vitamin B12 in the liver for several years, meaning it is not rapidly excreted and does not need to be consumed daily.

The Mechanism of Excretion and Why it Matters

The kidneys are responsible for filtering waste products and excess substances from the blood, a process that includes water-soluble vitamins. This efficient regulatory system ensures that high levels of these nutrients don't build up to toxic levels, as can be the case with some fat-soluble vitamins. However, this constant flushing means that a consistent daily intake from food or supplements is necessary to maintain optimal levels.

Comparison of Water-Soluble vs. Fat-Soluble Vitamins


Feature	Water-Soluble Vitamins	Fat-Soluble Vitamins
Storage	Limited storage capacity (except B12)	Stored in liver and fatty tissue
Excretion	Excess amounts excreted via urine	Not readily excreted; build up can lead to toxicity
Dietary Requirement	Needed consistently, often daily	Not needed daily due to bodily reserves
Absorption	Absorbed directly into the bloodstream	Absorbed with dietary fat into the lymphatic system
Examples	Vitamin C, B-complex vitamins	Vitamins A, D, E, and K

How to Ensure Adequate Intake of Water-Soluble Vitamins

Because they are not stored efficiently, it is important to include a variety of vitamin-rich foods in your daily diet. Food preparation methods can also affect the vitamin content, as heat and excessive water can destroy or wash out these nutrients. Steaming or microwaving can help minimize this loss compared to boiling.

Vitamin C: Found in citrus fruits, strawberries, peppers, broccoli, and leafy greens.
B-Complex Vitamins: Rich sources include whole grains, meats, eggs, dairy products, nuts, legumes, and green vegetables.

Conclusion

Understanding which water-soluble vitamins are excreted in urine highlights the importance of a consistent, healthy diet. The body's sophisticated filtration system ensures that most excess vitamin C and B-complex vitamins (with the notable exception of B12) are regularly eliminated. This process prevents toxicity but also means our bodies cannot build up large reserves. By focusing on a balanced diet rich in these essential nutrients, and being mindful of food preparation, you can ensure your body consistently receives what it needs for optimal health and function. For further reading, an excellent resource on the functions of these nutrients is available from the NIH's StatPearls publication on Biochemistry, Water Soluble Vitamins.

Frequently Asked Questions

The main difference is how the body handles them. Water-soluble vitamins dissolve in water and are not stored in the body, so excess amounts are excreted in urine. Fat-soluble vitamins are stored in the liver and fat tissues for future use.

All eight B-complex vitamins—Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantothenic Acid (B5), Pyridoxine (B6), Biotin (B7), and Folate (B9)—are excreted in the urine when consumed in excess. Vitamin B12 is the exception, as the body stores it in the liver.

The bright yellow color is primarily caused by excess riboflavin (vitamin B2) being excreted in the urine. It is a harmless side effect and simply shows that your body has absorbed what it needs, and the rest is being eliminated.

Yes, because the body does not store most water-soluble vitamins, a regular daily intake through diet or supplements is necessary to prevent deficiencies and ensure proper bodily functions.

It is difficult to reach toxic levels of water-soluble vitamins from food alone. However, excessive intake from high-dose supplements can cause adverse effects, such as gastrointestinal upset or, in rare cases, kidney stones with vitamin C.

Focusing on a well-balanced diet with a variety of fruits, vegetables, and other sources is key. Since water and heat can degrade these nutrients, minimize nutrient loss by opting for steaming over boiling vegetables and refrigerating fresh produce.

Water-soluble vitamins are involved in a wide range of functions, including energy production, cell metabolism, forming red blood cells, and supporting the nervous and digestive systems.