Vitamin B12 is a nutrient essential to the nervous system and healthy red blood cells. It is also important in the production of DNA - the genetic material present in all body cells. In addition to these key physiological functions, vitamin B12 may also be important to brain health.

People with age-related dementia are often found to have high levels of homocysteine in their blood which has been shown to increase chances for Alzheimer's disease. Studies show that vitamin B12 paired with folic acid and B6 can reduce homocysteine levels, but it is not certain whether this nutrient cocktail is helpful in the prevention or treatment of dementia.

An important review paper published in The Journal of Neuropsychiatry and Clinical Neurosciences earlier this year examined vitamin B12 deficiency in the elderly and the neuropsychiatric problems that accompany it. Findings indicated that vitamin B12 deficiency is indeed linked to neurologic, cognitive, psychotic and mood symptoms in older adults.

Another study from Chicago's Rush University Medical Center found that low vitamin B12 levels may contribute to shrinkage of the brain and consequent memory decline. The research examined 121 individuals from Chicago's south side who were aged 65 or older. Researchers drew blood from the participants to measure levels of vitamin B12 and B12-related markers that can signify a deficiency. Then they participated in testing measuring memory and cognition.

An average of 4.5 years later, brain imaging on the subjects showed that those with blood markers showing a vitamin B12 deficiency had smaller brains and scored lower on tests for memory, reasoning and cognition than individuals without B12 deficiency markers.

The lead author of the study, Christine C. Tangney, PhD, stated, "Our findings definitely deserve further examination. It's too early to say whether increasing vitamin B12 levels in older people through diet or supplements could prevent these problems, but it is an interesting question to explore."

Naturally found in many animal foods such as beef liver, clams, fish, meat, poultry, eggs and milk, vitamin B12 is also added to some breakfast cereals and other food products. Tangney recommended adding fortified breakfast cereals to the diet because "the vitamin does get into the body."

Vitamin B12 can also be found alone in supplement form or in most multivitamins and B-complex supplements. It is also available in sublingual (under the tongue) and nasal gel applications and by prescription as a shot (a typical treatment for deficiency).

Sometimes a vitamin B12 deficiency is associated with poor absorption. With aging, the stomach manufactures less acid which helps to break down vitamins. In addition, there are certain medications that older individuals take - like the diabetes drug metformin and drugs used to treat heartburn and stomach ulcers - that can impede the absorption of vitamin B12.

Lachner C, Steinle NI, Regenold WT. The neuropsychiatry of vitamin B12 deficiency in elderly patients. The Journal of Neuropsychiatry and Clinical Neurosciences. 2012 Dec 1;24 (1): 5-15.