Vitamin B-12, or cobalamin, is a complex substance needed for a variety of functions in the body, particularly nerve conduction and higher brain functions. It can be obtained from meat and plant sources, as well as sublingual supplements and injections. Consuming high levels of vitamin B-12, or mega-dosing, is considered safe and is sometimes used for those with Alzheimer's disease.
Requirements of Vitamin B-12
The amount of B-12 needed daily by an adult is not much, only about 2 to 3 mcg, according to "Vitamins: Fundamental Aspects in Nutrition and Health." However, because it is not readily absorbed from food or supplements, much larger amounts need to be consumed. As an example, taking 500 mcg of supplemental B-12, or cyanocobalamin, can result in only a couple of micrograms or so being absorbed, although it depends on the gastrointestinal health of the person. Consequently, multivitamins that contain between 100 and 200 mcg of synthetic cyanocobalamin do not meet daily requirements.
Mega-dosing Vitamin B-12
Due to its low rate of absorption, some health professionals recommend daily dosages of 1,000 mcg of B-12 taken under the tongue, or sublingually, which is supposed to enhance absorption. Others are partial to monthly intramuscular injections of much higher dosages. According to "Advanced Nutrition: Macronutrients, Micronutrients and Metabolism," there is no evidence supporting the idea that injections are better absorbed than sublingual supplements. Because B12 is water-soluble and not stored in the body for long, monthly mega-doses may be an inefficient method. Fortunately, B-12 supplements are extremely safe and essentially nontoxic, even in dosages thousands of times greater than recommended levels, according to "Nutrition and Public Health."
Alzheimer's Disease and B-12 Levels
Alzheimer's disease is a type of dementia that causes brain shrinkage, amyloid protein plaques and neurofibrillary tangles. Short-term memory loss, reduced cognitive abilities, confusion and inappropriate responses are common symptoms. According to "Human Biochemistry and Disease," some researchers estimate that up to 25 percent of those diagnosed with Alzheimer's may simply be chronically deficient in B-12, as the symptoms of the two conditions are almost indistinguishable. Normal blood levels of B-12 range from 200 to 600 picograms per milliliter, and a 2010 Finnish study found that those with the highest blood levels of B-12 were the least likely to be diagnosed with dementia. Recommended daily levels of B-12 for those experiencing dementia symptoms usually start at 2,000 mcg, although 1,000 mcg is thought to be enough to prevent deficiency symptoms in the elderly.
Sources of Vitamin B-12
The richest dietary sources of natural B-12, or cobalamin, are organ meats, especially the livers of lamb, pork and beef, according to "American Dietetic Association Complete Food and Nutrition Guide." Sources of B-12 include egg yolks, cheese and fish. Vegetables are considered poor sources, but include spinach, seaweeds, legumes and some nuts.
References
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism"; Carolyn D. Berdanier; 2009
- "Nutrition and Public Health"; Sari Edelstein; 2006
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Neurology"; Homocysteine and Holotranscobalamin and the Risk of Alzheimer's Disease: A Longitudinal Study; B. Hooshmand et al.; October 2010
- "American Dietetic Association Complete Food and Nutrition Guide"; American Dietetic Association; 2006
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