Up to one-in-eight people may have a vitamin B12 deficiency.
Vitamin B12 is crucial to the production of red blood cells and the healthy functioning of brain cells.
Its effect on mental processes is likely down to its involvement in the production of myelin.
Myelin is a material that surrounds neurons (brain cells) and also the connections between them, known as axons.
Fortunately, vitamin B12 deficiency is easy to correct either with supplementation or a change in diet.
Foods high in vitamin B12 include dairy, beef, salmon, eggs and low-fat milk.
