Vitamin B-12, also called cobalamin in its natural form, is a large complex molecule used for a variety of functions in your body. It plays especially important roles in brain function, metabolism and blood production. B-12 levels in your body can drop too low due to dietary deficiency, poor absorption or lack of synthesis by “friendly” bacteria in your intestines. Symptoms of B-12 deficiency are broad and can mimic senility, emotional disorders and musculoskeletal injuries.
Function of B-12
Vitamin B-12 is one of eight B vitamins involved in energy production by stimulating metabolism. B-12 is also needed for copying DNA during cell division, synthesizing red blood cells in bone marrow, transmitting electrical signals in nerves and assisting brain function, especially your short-term memory ability. Cell division is needed for growth and repair; red blood cells are needed to carry oxygen to all cells; and nerve transmission is needed for muscle contraction and healthy organ function.
The estimated amount of B-12 that your body needs each day is between 2 and 3 micrograms, depending on your body weight and activity level. However only a very small percentage is absorbed from dietary and supplemental sources. Absorption depends on stomach acidity -- lower is better -- and the production of a gastric substance called intrinsic factor. Often as people age, they produce less stomach acid and intrinsic factor, which puts them at risk for B-12 deficiency. B-12 levels are easily measured from a blood sample and normal values range from 200 to 600 picograms per milliliter of blood. Levels consistently below 200 picograms per milliliter of blood are too low and greatly increase the risk of deficiency symptoms.
Symptoms of Deficiency
All B vitamins are classified as water-soluble, which means excess amounts are excreted in urine, but B-12 lingers in the body for much longer than the other types. Consequently, symptoms of B-12 deficiency may take several months to manifest or become noticeable. In addition, another B vitamin called folic acid has many of the same functions of B-12, so some symptoms may be masked if you’re getting enough folic acid. Regardless, common symptoms from low levels of B-12 include poor short-term memory and concentration similar to Alzheimer’s disease; fatigue, weakness and pale skin due to deformed red blood cells; lack of energy and constipation from sluggish metabolism; moodiness and depression from brain dysfunction; and poor balance and numbness and tingling in the limbs from reduced nerve function. Low B-12 levels may also increase homocysteine levels in the blood, which is a risk factor for stroke and heart attack.
Small amounts of B-12 are made by certain species of bacteria in your large intestine, although they are easily destroyed by prescription antibiotics and dietary factors such as alcoholism. Animal products, including beef, pork, chicken, fish, seafood, dairy and eggs are excellent dietary sources of vitamin B-12. The richest source is shellfish such as clams, mussels and oysters. Vegetarians can get tiny amounts of B-12 from some varieties of yeast and edible seaweeds, but they are most at risk of deficiency, especially if they are elderly. Supplemental B-12, which is also called cyanocobalamin, is widely available in sublingual tablets or via injection by your doctor.
- Encyclopedia of Human Nutrition; Benjamin Caballero et al.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- Textbook of Functional Medicine; David S. Jones
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.