Vitamin B12: Deficiency Of Vitamin B12 And Tinnitus

Vitamin B12, also referred to as cobalamin and cyanocobalamin, is a micronutrient that is water soluble like other B vitamins. Unlike the other B vitamins, however, which are not stored in the body, vitamin B12 is stored for up to 9 months in the liver and kidneys.
The RDI for vitamin B12 is 2 lg for adults, 2.2 lg for pregnant women, and 2.6 lg for nursing mothers . Vitamin B12 is not found in vegetables, but can be found in pork, blue cheese, clams, eggs, herring, kidney, liver, seafood, and milk.
It has been estimated that 5% to 10% of persons over the age of 65 years are deficient in vitamin B12. With newer and more sensitive tests available, deficiency states have been found in as many as 15% to 20% of the population . This deficiency state is most likely secondary to absorption difficulties and a deficient nutritional intake. There may be some   correlation between the decline in vitamin B12 levels and the increasing prevalence of tinnitus in the elderly. Vitamin B12 is an important coenzyme required for the proper synthesis of DNA and new cell formation. It also works synergistically with vitamin C to aid in proper digestion and absorption of foods, protein synthesis, and the normal metabolism of carbohydrates and fats. Additionally, B12 prevents nerve damage by contributing to the formation of the myelin sheath. Vitamin B12 also maintains fertility, and helps promote normal growth and development in children. Metabolites, including cobalamin, are involved in stabilizing neural activity. Vitamin B12 is an essential cofactor for methylation of myelin basic protein and cell membrane phospholipids. Cobalamin deficiency has been shown to be a factor involved in neuronal dysfunction. It is logical to assume that a relationship between tinnitus, which might involve neuronal dysfunction, and vitamin B12 deficiency may exist. In the senior author’s experience, several patients who were motivated to attempt nutritional supplementation with B12 noted significant improvement in their tinnitus. Still others, however, have reported no such benefit. A deficiency of vitamin B12 can result in pernicious anemia, characterized by megaloblastic anemia, lack of intrinsic factor, inability to absorb vitamin B12, and increased risk for esophageal webs and cancer. Because vitamin B12 can be stored easily in the body and is only required in minute amounts, symptoms of severe deficiency usually take 3 to 5 years to appear. When symptoms do arise, usually in mid-life, it is likely that deficiency was caused by digestive disorders or malabsorption rather than poor diet. It is well known, however, that the elderly have a reduced dietary intake, which may predispose them to nutritional deficiencies. Furthermore, strict vegetarians (vegans) who do not consume any foods of animal origin need to supplement their diets with this nutrient because B12 comes almost exclusively from animal sources. Vitamin B12 is available in supplemental form. Because of relatively poor gastric absorption, B12 can be taken as a sublingual tablet or by injection. Supplements range in strength from 50 lg to 2 mg. Megadose vitamin B12 toxicity is unknown, and any excess is excreted from the body
. One can measure serum B12 or serum methylmalonic acid for levels of this vitamin. The normal range of B12 in the healthy population is 150 to 900 pg/mL.
Experimental studies and clinical observations have related tinnitus to demyelination of nerve fibers and to a distorted resting state of spontaneous neural activity. Shemesh et al  showed a high prevalence (47%) of vitamin B12 deficiency in patients with chronic tinnitus when a criterion of deficiency is set at 250 pg/mL and lower. Serum cobalamin deficiency was more widespread and severe in the tinnitus group associated with noise exposure. This suggested a relationship between vitamin B12 deficiency and dysfunction of the auditory pathway. Deficiency also results in peripheral and central neurologic pathology. Decreased methionine production caused by cobalamin deficiency can lead to a sensory demyelinating neuropathy. Abnormalities of the nervous system in the absence of hematologic disorders and normal results of the Schilling test have been reported in 28% of 141 consecutive patients with abnormally low serum cobalamin. The Schilling test assesses the absorption of free cobalamin and also the absorption of free cobalamin with intrinsic factor. In many instances, the actual cause of the deficiency is difficult to identify. It might be a result of inadequate dietary intake, a minor alimentary dysfunction, or a nutrition-metabolic disturbance. Supplemental cobalamin was found to show some relief in several patients with severe tinnitus.