What are the implications of my decreased urination after stopping a multivitamin, given my history of polyuria and normal electrolyte levels?

Your Laboratory Findings Indicate Transient Polyuria from Multivitamin-Induced Osmotic Diuresis, Not a Pathological Condition

Your laboratory values during the polyuria episode (serum osmolality 300 mOsm/kg, urine osmolality 170 mOsm/kg, serum sodium 143 mEq/L, urine sodium 39 mEq/L) demonstrate water diuresis with appropriate renal function, and the resolution of symptoms after stopping the multivitamin confirms this was a benign, self-limited phenomenon that requires no further intervention.

Understanding Your Laboratory Pattern

Your serum osmolality of 300 mOsm/kg with a urine osmolality of 170 mOsm/kg indicates water diuresis rather than osmotic diuresis 1. In water diuresis, urine osmolality is typically <150-200 mOsm/kg, which matches your presentation 1, 2.

• Your normal serum sodium (143 mEq/L) and normal urine sodium (39 mEq/L) indicate appropriate renal handling of electrolytes during this episode 3, 1
• The urine osmolality of 170 mOsm/kg falls in the range consistent with dilute urine from increased water intake or mild impairment in urinary concentration 4, 1
• Your previous serum osmolality of 289 mOsm/kg represents normal baseline kidney function 3

Why the Multivitamin Caused Polyuria

Multivitamins can induce polyuria through osmotic diuresis when they contain high doses of water-soluble vitamins (B-complex, vitamin C) and minerals that are excreted renally 2.

• When solute excretion increases, obligatory water loss follows, leading to increased urine volume 5, 2
• Your anxiety may have contributed to increased fluid intake (primary polydipsia), creating a mixed picture of both solute and water diuresis 2
• The resolution of polyuria after stopping the multivitamin confirms this was the causative factor 2

Why This Is Not Concerning

Your clinical scenario represents a benign, reversible condition with complete resolution after removing the inciting factor. Several key points confirm this:

• Normal serum sodium throughout indicates intact osmoregulation 3, 1
• Appropriate urine sodium excretion demonstrates normal tubular function 3
• Resolution of symptoms after stopping the multivitamin proves causality 2
• No evidence of diabetes insipidus: your urine osmolality of 170 mOsm/kg is above the typical threshold (<150 mOsm/kg) seen in nephrogenic diabetes insipidus 4

What You Should Monitor Going Forward

No specific monitoring or intervention is required given complete symptom resolution, but consider the following if polyuria recurs:

• Avoid high-dose multivitamins or those with excessive water-soluble vitamins 2
• If polyuria recurs without clear cause, measure 24-hour urine volume and osmolality to distinguish between water diuresis (urine osmolality <150 mOsm/kg) and osmotic diuresis (urine osmolality >300 mOsm/kg) 1, 2
• Anxiety-related increased fluid intake can perpetuate polyuria even without osmotic load 2
• Annual monitoring of serum sodium and osmolality is reasonable if you have ongoing anxiety-related polydipsia 4

When to Seek Medical Attention

Seek evaluation only if you develop:

• Persistent polyuria (>3 liters/day) despite normal fluid intake and no multivitamin use 1, 2
• Hypernatremia (serum sodium >145 mEq/L) with polyuria, which could indicate diabetes insipidus 4
• Inability to concentrate urine after overnight fluid restriction 4

Your current situation requires no treatment, no further testing, and no dietary restrictions beyond avoiding excessive multivitamin supplementation.