Vegetarians and Vitamin B12
~ June 2000 No.104 ~
People’s eating habits are influenced by many things - their age, ethnic background, economic status, religious beliefs. The growing relationship between diet and health has prompted many to make major changes in their diet. Vegetarian diets have become popular for many reasons besides concern about health. It’s obviously one way to avoid red meats, dairy and poultry products, all of which have been linked to a variety of chronic diseases. No matter what prompts someone to turn to a vegetarian diet, there may be dangers if proper precautions aren´t taken to ensure a well balanced diet.
There are several degrees of vegetarianism, but the strictest vegan diet contains no animal products at all. Vegan diets are typically contain large amounts of fruits and vegetables. Legumes such as beans, peas and lentils along with grains are the major sources of protein. Nuts and vegetable oils provide energy. The large emphasis on fruits and vegetables in the vegan diet should ensure an adequate daily supply of vitamins. But there is one important exception. Vitamin B12. The main source of this vitamin in most diets is red meat, organ meats, eggs and milk. Small quantities are found in soybeans, green beans, beets, carrots and peas. Anyone on a strict vegan diet may have to include a vitamin supplement that includes vitamin B12 to keep their B12 levels up.
Vitamin B12 is involved in a variety of metabolic functions in the liver, often acting as a co-enzyme. It is involved in both amino acid / protein metabolism and the synthesis of fats.
A recent letter published in the New England Journal of Medicine reported on the case of a patient who had been a strict vegan for 13 years. This patient had severe vision loss and tests showed below normal blood levels of thiamin, vitamin A, vitamin C, vitamin D, vitamin E, zinc, selenium and vitamin B12. The patient was given large doses of vitamins that quickly raised his blood vitamin levels. However, the damage to his eyesight was permanent. The attending doctors speculated that the loss of eyesight was due to the deterioration of the optic nerve that may have resulted from long term low vitamin B12 intake .
Vegans can lead a healthy life, but intelligent selection of foods is a very important for those who choose this type of diet. It has been suggested that vitamin supplements should be included in a vegetarian diet. Either way, vitamin B12 is one vitamin that vegetarians should be very aware of, since the long term damage from vitamin B12 deficiency may not be reversible.
NEJM 342: 897-898 (2000)