What is the cause of cloudy urine in an adult patient with no significant medical history, occurring 1 hour after taking 100mg of thiamine (Vitamin B1) and resolving when the supplement is not taken?

Cloudy Urine After Thiamine Supplementation

The cloudy urine occurring 1 hour after taking 100mg thiamine is almost certainly excess thiamine being excreted in the urine, which is a normal physiological response when tissue saturation is reached—this is harmless and requires no intervention. 1

Mechanism of Thiamine Excretion

When thiamine intake exceeds the body's immediate needs and tissue saturation capacity, the excess is rapidly excreted through the kidneys, which can cause visible changes in urine appearance 1:

• Thiamine has limited body storage (only 25-30mg total in adults) with a relatively short half-life of active forms 2
• Once tissues are saturated, additional thiamine appears in urine either as pyrimidine metabolites or unchanged thiamine 1
• Doses exceeding 30mg three times daily are not utilized effectively by the body, with the surplus being excreted 1
• The 1-hour timeframe aligns perfectly with thiamine's absorption and excretion kinetics—thiamine is rapidly absorbed in the jejunum and ileum, and excess is quickly filtered by the kidneys 2

Why 100mg Causes Visible Urine Changes

The recommended dietary allowance (RDA) for thiamine is only 1.1-1.2 mg/day for healthy adults 2, 3:

• Your 100mg dose is approximately 80-90 times the daily requirement 2
• Standard parenteral nutrition contains only 2.5-6 mg/day, which prevents deficiency in most patients without causing visible urinary changes 3
• Even therapeutic doses for mild deficiency are only 10 mg/day 3, 4

At this supraphysiologic dose, the body cannot utilize the majority of the thiamine, so it is excreted within hours, creating the cloudy appearance 1.

Safety Considerations

This is completely harmless and does not indicate toxicity 3, 1:

• No upper limit for thiamine toxicity has been established—excess is simply excreted in urine 3, 1
• Parenteral doses of 100-500mg have been administered without toxic effects 1
• High doses rarely cause any adverse effects; doses >400mg may occasionally induce mild nausea, anorexia, or mild ataxia, but these are uncommon 3

Clinical Correlation

The temporal relationship you've observed (cloudy urine only on days when thiamine is taken, absent on days without supplementation) definitively confirms this is thiamine excretion 1, 5:

• Urinary thiamine excretion correlates directly with oral dose 5
• The excretion occurs within hours of ingestion and returns to baseline within 18-24 hours 6
• This pattern is exactly what would be expected with intermittent supplementation 5

Recommendation

Continue the supplement if there is a clinical indication for thiamine supplementation, or discontinue if taking it without medical necessity 2, 3:

• If you have risk factors for thiamine deficiency (alcohol use disorder, malnutrition, chronic diuretic use, post-bariatric surgery, malabsorption), continue the supplement 3
• If you are a healthy individual without risk factors, the RDA of 1.1-1.2 mg/day from diet is sufficient, and 100mg supplementation is unnecessary 2
• The cloudy urine itself requires no treatment—it is simply visual evidence of renal thiamine excretion 1