Can taking a regular multivitamin (MV) cause an increase in urination?

Can Multivitamins Cause Increased Urination?

Yes, certain components in multivitamins—particularly high-dose vitamin C and calcium—can increase urination frequency and urgency, though this effect is dose-dependent and not universal.

Mechanism and Evidence

Water-Soluble Vitamins and Urinary Excretion

The primary mechanism relates to how water-soluble vitamins are processed by the body:

• Water-soluble vitamins (B-complex and vitamin C) are not stored in significant amounts and excess is excreted by the kidneys, which inherently increases urinary output 1
• Daily parenteral doses of water-soluble vitamins are typically several times higher than oral recommended allowances specifically due to increased urinary excretion 1

Specific Vitamin Effects on Urination

Vitamin C shows the strongest evidence for affecting urination patterns:

• High-dose vitamin C (≥500 mg/day from diet and supplements combined) significantly increases storage symptoms, particularly combined frequency and urgency, with women consuming this amount being 3.42 times more likely to report these symptoms compared to those consuming <50 mg/day 2
• This effect appears dose-dependent, with the association becoming clinically significant at supplemental doses well above the recommended dietary allowance 2

Calcium supplementation also demonstrates clear urinary effects:

• Calcium supplements ≥1000 mg/day are associated with a 2-fold increase in urinary storage symptoms (OR: 2.04; 95% CI, 1.35-3.09) 2
• This occurs through increased urinary calcium excretion, which can affect bladder function 1

Clinical Context and Caveats

Not All Multivitamin Users Affected

• The urinary effects are symptom-specific and dose-dependent, meaning standard multivitamin formulations at recommended doses may not cause noticeable changes in most users 2
• Approximately 35% of adults in the United States regularly use multivitamin-multimineral products, yet increased urination is not reported as a widespread complaint 3

Safety Profile

• Minor adverse effects like nonspecific gastrointestinal symptoms are the most commonly reported side effects of multivitamin use, with no significant differences between treatment and placebo groups in long-term studies 4
• Long-term multivitamin use within the range of dietary reference intake is considered safe and does not increase mortality 4

Practical Recommendations

If you experience increased urination after starting a multivitamin:

• Check the vitamin C content—formulations with >500 mg may be contributing to frequency and urgency 2
• Review calcium supplementation—doses ≥1000 mg/day are more likely to cause storage symptoms 2
• Consider switching to a formulation with lower doses of these specific nutrients while maintaining adequate intake of other vitamins and minerals 2
• The effect should resolve within days of reducing or discontinuing the high-dose components, given the rapid renal excretion of water-soluble vitamins 1

Important distinction: Dietary vitamin C from foods and beverages is actually inversely associated with voiding symptoms, so the issue is specifically with high-dose supplementation, not food sources 2.