A letter in New Scientist correcting some misinformation about B12. It’s probably for subscribers only -

Writing about diet supplements, Linda Geddes says that water-soluble vitamins cannot be stored (1 December, p 30). Vitamin B12 is water soluble, but it is stored, mainly in the liver. The amount stored can be enough to satisfy the body's needs for years.

This is one reason why a vitamin B12 deficiency can be hard to diagnose. Even if somebody cannot absorb any B12 – for example in pernicious anaemia – levels in the body can decrease very slowly. Many people put symptoms such as fatigue, memory lapses and clumsiness down to increasing age. Often it is only when severe signs of harm arise, such as peripheral neuropathy, in which nerves are damaged, that someone visits a doctor. It is then often too late to completely fix the damage.