A body with a full store of B12 can go without B12 for years before there is any deficiency. It's something to definitely keep in mind, but it's probably a bit overhyped as you only really need to take B12 one month in a year or so.
Mayo Clinic Vitamin B12
Mayo Clinic Vitamin B12
Quote:The human body stores several years' worth of vitamin B12 in the liver, so low levels in the body are rare.