Can riboflavin (Vitamin B2) cause frequent urination?

Riboflavin Does Not Cause Frequent Urination

Riboflavin (vitamin B2) does not cause frequent urination as a side effect. The only urinary effect documented in high-quality guidelines is harmless yellow-colored urine, which is simply excess riboflavin being excreted 1.

Evidence from Clinical Guidelines

The 2022 ESPEN micronutrient guidelines, which represent the most authoritative and recent evidence on riboflavin safety, explicitly state that riboflavin consumed orally from diet or multivitamin supplements rarely causes side effects, with the only notable effect being yellow-colored urine 1. This yellow discoloration is a benign finding that occurs because riboflavin is water-soluble and excess amounts are readily excreted through the kidneys 1.

Documented Side Effects

The actual side effects of riboflavin supplementation are minimal and well-characterized:

• Yellow-colored urine is the most common and harmless effect at standard doses 1
• Diarrhea has been reported rarely, occurring in only one patient out of 55 in a high-dose migraine prophylaxis trial using 400 mg daily 2
• Polyuria (increased urine production) was reported in a single case in the same trial, but this was one isolated event among thousands of patients studied and does not establish causation 2

Important Context on the Single Polyuria Report

The one mention of polyuria in the literature comes from a 1998 migraine prophylaxis study where a patient taking 400 mg of riboflavin daily (over 300 times the RDA) reported increased urination 2. However:

• This was one case out of 55 participants in that specific trial 2
• The dose used (400 mg) was pharmacologic, not nutritional - far exceeding the RDA of 1.1-1.3 mg/day 3
• No other studies or guidelines mention polyuria or frequent urination as a riboflavin side effect 1
• The event was classified as minor and not serious 2

Riboflavin Metabolism and Urinary Excretion

Riboflavin's pharmacokinetics explain why frequent urination is not a concern:

• Riboflavin is not stored in the body in ample amounts, requiring constant dietary supply 1
• Excess riboflavin is excreted in urine through normal kidney function, not through increased urine volume 1
• The yellow urine color reflects riboflavin concentration, not increased urine production 1
• Even in elderly subjects consuming adequate riboflavin, small supplemental amounts are not retained but simply excreted 4

Clinical Reassurance

If you are experiencing frequent urination while taking riboflavin, look for alternative causes. The evidence strongly indicates this is coincidental rather than causal. Common alternative explanations include:

• Increased fluid intake
• Caffeine or diuretic medications
• Diabetes or prediabetes
• Urinary tract conditions
• Prostate issues (in men)
• Overactive bladder

The safety profile of riboflavin is excellent, with the ESPEN guidelines confirming that standard doses have minimal adverse effects 1, 5. Even repeatedly consumed pharmacologic doses above 100 mg have potential toxicity concerns related to oxidative stress and hepatotoxicity, but not urinary frequency 1.