High-Dose Vitamin B12 and Frequent Urination
The 1000mcg of vitamin B12 in your bariatric multivitamin is almost certainly causing your frequent urination, as urinary excretion of vitamin B12 is strongly dependent on urine volume rather than intake level. 1
Why This Happens
Vitamin B12 excretion drives increased urine production. When you take high-dose B12 supplementation (like the 1000mcg in your bariatric vitamin), your kidneys must excrete the excess through urine. Research demonstrates that urinary vitamin B12 output is strongly correlated with urine volume (r = 0.683-0.897), meaning as your body eliminates the B12, it simultaneously increases urine production. 1
Importantly, even when subjects were given 1.5mg of cyanocobalamin (500-fold higher than daily requirements), urinary B12 content only increased 1.3-fold, but the correlation between B12 excretion and urine volume remained extremely strong. 1 This means your body is producing more urine to eliminate the B12, rather than simply concentrating it in your existing urine output.
Is This Dose Necessary for You?
For most bariatric surgery patients, 1000mcg daily oral B12 is higher than guideline recommendations. The standard recommendation is 250-350mcg daily oral supplementation, with 1000mcg reserved for weekly dosing or specific deficiency treatment. 2, 3
Guideline-Based Dosing:
- Routine supplementation after bariatric surgery: 250-350mcg daily orally 3
- Alternative regimen: 1000mcg weekly (not daily) 3
- Intramuscular injections: Every 3 months after RYGB or malabsorptive procedures 2, 4
What You Should Do
Consider switching to a bariatric multivitamin with 250-350mcg B12 instead of 1000mcg. 3 This lower dose:
- Still prevents deficiency effectively 2
- Reduces the urinary excretion burden 1
- Should significantly decrease your frequent urination
Important Caveats:
- Do not stop B12 supplementation entirely - bariatric surgery patients require lifelong B12 supplementation due to reduced absorption 2
- Check your B12 levels before making changes, especially if you're more than 6 months post-surgery 2, 4
- If your levels are borderline (180-350 pg/mL), you may need methylmalonic acid testing to confirm adequate functional B12 status 2, 5
When Higher Doses Are Needed:
You should continue the 1000mcg daily dose if you have:
- Documented B12 deficiency (serum B12 <180 pg/mL) 6
- Neurological symptoms (numbness, tingling in limbs) 2, 4
- Malabsorptive procedures like BPD/DS 2
- Inability to receive intramuscular injections 7
The Calcium Connection
The absence of calcium in your multivitamin is actually appropriate for optimal absorption. Calcium and B12 should ideally be taken separately, though this isn't the cause of your urinary symptoms. 2 Iron and calcium need to be taken 1-2 hours apart to avoid absorption interference, but you'll need a separate calcium supplement (1200-1500mg daily from food and supplements) after bariatric surgery. 2