Vitamin B12 Does Not Cause Dark Urine
Vitamin B12 supplementation at 1000 mcg does not cause dark urine. B12 is a water-soluble vitamin that is excreted in urine, but it does not darken urine color even at very high doses.
Evidence from Controlled Studies
The most direct evidence comes from a controlled trial specifically examining this question:
- A study of 30 healthy volunteers given vitamin B12 at approximately 200 times the recommended dietary allowance found no change in urine color despite massive increases in urinary B12 concentration 1
- In this trial, urinary B12 concentration increased dramatically (from baseline to supplemented levels), yet urine color remained unchanged and within the euhydrated classification range 1
- Two independent observers assessed urine color using a standardized eight-point color chart, confirming no significant difference between supplemented and non-supplemented conditions 1
Urinary Excretion Characteristics
Understanding how B12 is excreted helps explain why it doesn't darken urine:
- Urinary excretion of vitamin B12 is primarily dependent on urine volume, not on B12 intake 2
- When 20 Japanese adults were given 1.5 mg of cyanocobalamin (500-fold higher than daily intake), urinary B12 content increased by only 1.3-fold, demonstrating that excess B12 is not simply dumped into urine in large quantities 2
- After injection of 100-1000 mcg of vitamin B12, 50-98% may appear in urine within 48 hours, with the major portion excreted within the first 8 hours, but this does not alter urine color 3
What Actually Causes Dark Urine
If you are experiencing dark urine while taking B12, consider these alternative causes:
- Dehydration (concentrated urine appears darker)
- Liver or biliary disease (bilirubin causes brown/tea-colored urine)
- Hemolysis or rhabdomyolysis (myoglobin or hemoglobin causes red-brown urine)
- Medications (many drugs can darken urine)
- Foods (beets, blackberries, rhubarb)
Clinical Implications
- B12 supplementation at 1000 mcg is a standard therapeutic dose for deficiency treatment and is safe 4
- This dose does not interfere with hydration assessment via urine color 1
- Dark urine occurring coincidentally with B12 supplementation requires evaluation for other causes
- If dark urine persists, discontinue the B12 temporarily to confirm it is not the cause, though this is highly unlikely based on available evidence 1