Can Drinking Too Much Water Flush Out B12?

November 12, 2025 •

4 min read

Vitamin B12 is a water-soluble vitamin, meaning it dissolves in water, and any excess is typically excreted through urine. The idea that drinking too much water can flush out B12 is a common concern, but the reality is more nuanced, involving the body's natural regulatory systems and the specific properties of this essential nutrient.

Quick Summary

Excess vitamin B12, being water-soluble, is naturally filtered by the kidneys and eliminated in urine, but moderate overhydration will not cause a deficiency. The body's ability to excrete surplus B12 prevents toxicity, while significant overconsumption of water can affect electrolyte balance rather than vitamin levels.

Key Points

Water-Soluble Nature: Vitamin B12 dissolves in water, and the body naturally excretes any excess through urine, not due to an imbalance from water intake.
Controlled Absorption: The body controls B12 absorption in the small intestine, and the liver stores several years' worth of reserves, making it resilient to fluctuations from hydration levels.
Moderate Intake Is Safe: Normal to high-normal water consumption will not cause a B12 deficiency; the kidneys are highly efficient at regulating what is excreted.
Excess Water Risks: The real danger of drinking excessively large amounts of water is hyponatremia (low sodium levels), a life-threatening electrolyte imbalance, not vitamin loss.
Supplementation vs. Diet: Large doses from supplements may lead to more excretion, but this is a natural process and not harmful; diet-based B12 is handled very efficiently by the body.
Focus on Balance: For optimal health, focus on consistent, healthy hydration and a balanced diet to support your body's natural vitamin regulation.

Understanding Water-Soluble Vitamins

Vitamin B12, also known as cobalamin, is a key member of the B-complex family. A defining characteristic of this group is their solubility in water. Unlike fat-soluble vitamins (A, D, E, K), which are stored in the liver and fatty tissues, water-soluble vitamins are not stored for long periods. The body absorbs what it needs, and the kidneys excrete the rest in urine. This natural process is a safety mechanism that prevents the accumulation of toxic levels of these vitamins. For this reason, a tolerable upper intake level (UL) has not been set for B12, as excess intake via diet is generally considered safe.

The Body's Regulatory Process and B12

The body has a sophisticated system for managing nutrient levels. When it comes to vitamin B12, absorption primarily occurs in the small intestine, specifically the ileum, after it has bound to intrinsic factor, a protein secreted in the stomach. The amount of B12 that can be absorbed this way is limited. Once absorbed, B12 is transported through the body to be used in vital functions, including nerve function, DNA synthesis, and red blood cell formation. The liver also has a large storage capacity for B12, holding reserves for several years. This dual mechanism of controlled absorption and efficient storage means that a sudden, temporary increase in fluid intake is unlikely to significantly impact long-term B12 levels.

Can Excessive Water Intake Impact B12?

While the body will excrete any surplus water-soluble vitamins with increased urination, it would require an extreme level of water intake, far beyond normal hydration, to have any noticeable effect on B12 levels. The amount of B12 lost through urine is relatively small compared to the body's overall stores. The more immediate and serious risk of drinking dangerously excessive amounts of water, a condition known as hyponatremia, is the dilution of sodium levels in the blood, which can be life-threatening. It is this electrolyte imbalance, not vitamin deficiency, that is the primary concern with hyperhydration. Healthy kidney function ensures that the excess fluid is filtered and excreted, taking with it only the water-soluble vitamins that the body does not need at that moment.

Normal Hydration vs. Hyperhydration

Normal hydration—drinking a healthy amount of water based on thirst and activity level—is crucial for overall health and supports the body's natural processes, including nutrient absorption. Hyperhydration, or water intoxication, is a dangerous and rare condition that occurs when water intake overwhelms the kidneys' ability to excrete it. During this process, electrolytes and trace amounts of water-soluble nutrients, including B12, can be lost, but the primary danger remains the severe disruption of sodium levels. A healthy individual with a balanced diet does not need to worry about flushing out their B12 with a few extra glasses of water.

Water-Soluble vs. Fat-Soluble Vitamins

To clarify how the body handles different types of nutrients, it's helpful to compare water-soluble and fat-soluble vitamins.


Feature	Water-Soluble Vitamins (e.g., B12, Vitamin C)	Fat-Soluble Vitamins (e.g., A, D, E, K)
Storage	Limited storage; excess is excreted via urine.	Stored in the liver and fatty tissues.
Toxicity Risk	Low toxicity risk as excess is eliminated.	High toxicity risk if consumed in excessive doses.
Absorption	Dissolve in water; absorbed directly into the bloodstream.	Dissolve in fat; absorbed with dietary fats.
Frequency of Intake	Regular, daily intake often recommended due to limited storage.	Not needed daily; body draws from stored reserves.
Vulnerability	Easily destroyed or lost during cooking and food processing.	More stable during cooking.

Conclusion

While it is technically true that excess B12 is flushed out of the body in urine, the notion that drinking a healthy or even a moderately high amount of water can cause a B12 deficiency is a myth. The body's sophisticated systems for absorption, transport, and storage of B12, along with its ability to excrete excess water-soluble vitamins, prevent this from happening. The real dangers of excessive hydration are related to electrolyte imbalances, not vitamin loss. For those with consistently elevated B12 levels due to supplementation or underlying health issues, increasing water intake is sometimes suggested as a safe way to help the body naturally excrete the surplus. A healthy individual should focus on staying properly hydrated and maintaining a balanced diet, without worrying about washing away their essential vitamins.

Supporting Your B12 Levels

To ensure adequate B12 intake, focus on a balanced diet rich in sources like meat, fish, eggs, and fortified cereals. If you have concerns about deficiency, or are a vegan or vegetarian, consider supplementation, but always with a healthcare professional's guidance. The key is to support your body's natural functions with consistent, adequate nutrient intake and healthy hydration habits.

Source: National Institutes of Health

Note: This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a healthcare provider with questions about your health.

Frequently Asked Questions

No, drinking more than 8 glasses of water a day will not cause a B12 deficiency in a healthy individual. The body effectively absorbs the B12 it needs and excretes only the excess, a natural process not harmed by staying well-hydrated.

The primary risk of drinking dangerously excessive amounts of water, a condition called hyponatremia, is the dilution of sodium in the blood. This is a severe electrolyte imbalance and is not related to flushing out vitamins.

It is extremely difficult to overdose on vitamin B12 through diet or standard supplementation. Because it is water-soluble, any excess is typically eliminated in the urine, and no tolerable upper intake level (UL) has been established due to its low toxicity.

When you take large doses of B12 supplements, your body absorbs what it can, and the remainder is excreted through urine within a few hours. This is a normal process and does not mean your body is not getting enough B12.

The body stores Vitamin B12 primarily in the liver. This storage can provide a reserve for several years, ensuring a stable supply of the vitamin even with variations in daily intake.

Dehydration is not a known cause of altered B12 levels. Factors such as over-supplementation, kidney disease, and liver disease are more likely to affect B12 levels than a person's hydration status.

No, you cannot prevent the natural process of excreting excess water-soluble vitamins like B12. This is how the body regulates its nutrient levels. Trying to inhibit this process would be unnecessary and potentially harmful.