Readers here may want to read How to avoid dementia DR. MALCOLM KENDRICK The paper Dr Kendrick is discussing is available online
It may also be worth pointing out B vitamins (along with some other vitamins) are made for us by our gut microbiota.
Bacteria as vitamin suppliers to their host: a gut microbiota perspective
Diet-Microbiota Interactions and Their Implications for Healthy Living
We should all be making more effort to restore our natural gut flora particularly after using antibiotics. We should also be aware that older people who may be on a restricted diet and may be vulnerable to repeat UTI infections may require and alternative source of B Vitamins if their gut microbia is subject to regular antibiotic exposures.
There are plenty of B Vitamin complex supplements to choose from
I use Thorne Research, B-Complex #12, 60 Veggie Caps
If you use this code WAB666 you can get an introductory discount at IHERB.