You're well beyond any knowledge or ideas I would have, except to see an MD. You'll clearly of a scientific bent yourself and have thought through the situation logically. Stop back and let us know what you find out, okay? Best wishes --
I haven't changed my diet and don't take antacids.
My diet is organic and/or all-natural.
Are you taking antacids? I've read something that says the chemicals/materials in antacids can affect urination frequency.
Do you change anything else in your intake other than the B vitamins?
I drink about 3 litres of water throughtout the day and urinate maybe once or twice when taking the B-Complex.
Nothing else but the B-Complex causes this; otherwise I urinate regularly.
And Vitamin-B doesn't pass out of your system as quickly as you think despite water solubility. B-12 alone takes up to a week.
I think I've read that all the Bs are water soluble, so they should pass out of your system quickly, I would guess (but I'm not medically trained, so don't know for sure).
I too take B complex supplements, some of which run up into the thousands% of daily requirement, like B-1, which is 3,333% of MDR.
Given that the Bs are supposed to just wash out of your body, it seems like it might be something else, but this is a question for your doc.
Are you keeping your fluid intake up? What else are you taking?