Vitamin B12 is a neuroprotective, water-soluble vitamin that is naturally found in animal products including fish, meat, poultry, eggs, milk, and milk products. Vitamin B12 is generally not present in plant foods, but fortified breakfast cereals are a readily available source of vitamin B12 with high bioavailability for vegetarians. Some nutritional yeast products also contain vitamin B12. It is available as a dietary supplement and a prescription medication. Vitamin B12 exists in several forms and contains the mineral cobalt, so compounds with vitamin B12 activity are collectively called “cobalamins”. Methylcobalaminand 5-deoxyadenosylcobalamin are the forms of vitamin B12 that are active in human metabolism.
Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis. A deficiency is characterised by megaloblastic anaemia, fatigue, weakness, constipation, loss of appetite, and weight loss. Neurological changes, such as numbness and tingling in the hands and feet, can also occur. Additional symptoms of vitamin B12 deficiency include difficulty maintaining balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue. Low levels of B12 have been associated with peripheral neuropathy, cognitive impairment, and more rapid rate of disease progression in Parkinson’s.
The neurological symptoms of vitamin B12 deficiency can occur without anaemia, so early diagnosis and intervention is important to avoid irreversible damage.