Can Multivitamins Cause Increased Urination and Low Urine Osmolality?
Multivitamins containing water-soluble B-vitamins can cause increased urination, but a urine osmolality of 300 mOsm/L is not considered low and does not indicate a pathological polyuria.
Understanding Your Urine Osmolality Result
- Your urine osmolality of 300 mOsm/L is actually normal to slightly concentrated, not low 1
- True hyposthenuria (low urine concentration) is defined as urine osmolality <150 mOsm/L**, while osmotic polyuria shows values **>300 mOsm/L 1
- Your value sits right at the threshold, indicating your kidneys were concentrating urine appropriately despite increased volume 1
How Multivitamins Can Increase Urination
Water-Soluble B-Vitamins and Urine Volume
- Vitamin B12 excretion is directly dependent on urine volume - when you take B-vitamins, your body increases urine output to excrete the excess 2
- In a study where adults took 500-fold higher than normal B12 doses, urinary B12 increased only 1.3-fold, but urine volume increased substantially to facilitate excretion 2
- This relationship between B12 and urine volume was strongly correlated (r = 0.683-0.897) across multiple studies 2
Vitamin D and Urinary Flow
- Vitamin D in multivitamins can increase urine flow rate through effects on bladder function and detrusor muscle 3
- Higher serum vitamin D concentrations are significantly associated with increased urine flow rate (β coefficient: 0.003-0.004, p < 0.001) 3
- This effect persists across all age groups and both sexes 3
Other Water-Soluble Vitamins
- Vitamin C at doses ≥1000 mg increases urinary oxalate excretion by 22%, which requires increased water excretion 4
- Excess riboflavin (vitamin B2) causes bright yellow urine and increased urinary output as the body eliminates the surplus 5
- Older adults show greater plasma increases of thiamine, riboflavin, and pantothenic acid after multivitamin ingestion, potentially leading to more urinary excretion 5
Why Your Symptoms Resolved
- Water-soluble vitamins are not stored in significant amounts and excess is rapidly excreted by the kidneys within 24-72 hours 4
- Once you stopped the multivitamin, your body cleared the excess B-vitamins and vitamin C, eliminating the osmotic drive for increased urination 2, 5
- The return to normal urination patterns confirms this was a benign, reversible effect of vitamin supplementation 2
Clinical Significance and Reassurance
- This is not pathological polyuria - true polyuria is defined as urine output >3 liters per 24 hours with inappropriately dilute urine 1
- Your experience represents normal physiological excretion of excess water-soluble vitamins 2, 5
- The fact that your urine osmolality was 300 mOsm/L (not <150) indicates your kidneys were functioning normally to concentrate urine appropriately 1
Important Caveats
When to Be Concerned About Multivitamins
- Avoid vitamin C supplements >1000 mg/day if you have a history of kidney stones, as this increases oxalate and stone risk by 40% 4
- Avoid multivitamins containing vitamin D if you have hypercalcemia or hypercalciuria, as this can worsen nephrocalcinosis 4, 6
- In children with Williams syndrome or other calcium metabolism disorders, multivitamins with vitamin D should be avoided entirely 4
Normal vs. Pathological Polyuria
- If you were truly producing >3 liters of urine daily with osmolality <150 mOsm/L, this would warrant evaluation for diabetes insipidus or primary polydipsia 1
- Osmotic polyuria (from diabetes mellitus, for example) shows urine osmolality >300 mOsm/L, which is different from your situation 1
Bottom Line
Your increased urination while taking the multivitamin was a normal physiological response to excess water-soluble vitamins, particularly B-vitamins and possibly vitamin D 2, 3. Your urine osmolality of 300 mOsm/L was not abnormally low and indicates proper kidney function 1. The resolution of symptoms after stopping the multivitamin confirms this was a benign, self-limited effect requiring no treatment 2, 5.