Urine Color Changes with Iron and Vitamin B12 Supplements
Neither ferrous sulfate nor vitamin B12 tablets cause concentrated yellow urine at therapeutic doses. Vitamin B12 supplementation at extremely high doses (200× the recommended dietary allowance) does not alter urine color in euhydrated individuals, and ferrous sulfate has no documented effect on urine color 1.
Vitamin B12 and Urine Color
High-dose vitamin B12 supplementation does not change urine color. A controlled study administering vitamin B12 at approximately 200 times the recommended dietary allowance overnight found no difference in urine color between supplemented and non-supplemented trials in euhydrated volunteers 1.
Urine color remained within the euhydrated classification (4-5 on an 8-point scale) despite massive increases in urinary B12 concentration, demonstrating that even supraphysiologic doses do not confound colorimetric assessment of hydration status 1.
The common belief that B vitamins cause bright yellow urine may stem from vitamin B2 (riboflavin) in multivitamin preparations, not B12 specifically 1.
Ferrous Sulfate and Urine Color
Ferrous sulfate does not cause yellow urine. There is no documented evidence in clinical guidelines or research literature that iron supplementation alters urine color to yellow 2.
Standard therapeutic doses of ferrous sulfate (200 mg tablets providing 65 mg elemental iron) are well-characterized for gastrointestinal side effects but not for urine discoloration 2, 3.
Iron supplements may darken stool color due to unabsorbed iron in the gastrointestinal tract, but this is distinct from urine color changes 2.
Clinical Interpretation
Concentrated yellow urine typically indicates dehydration or concentrated urine, not medication effects 1.
If a patient reports yellow urine while taking these supplements, assess hydration status through urine specific gravity (<1.020 suggests adequate hydration) and urine osmolality (<700 mmol/kg suggests euhydration) rather than attributing it to the medications 1.
Other medications, particularly certain antibiotics, phenazopyridine, or multivitamins containing riboflavin (B2), are more likely culprits for yellow urine discoloration 1.