Folate, Vitamin B12 and Homocysteine Levels in Patients with Confirmed Alzheimer’s Disease

Homocysteine is a toxic amino acid produced in the body and a byproduct of the amino acid methionine.  Increased homocysteine levels are thought to cause narrowing and hardening of the arteries and may be linked to the formation of blood clots.

According to a 2002 report from Boston University, the presence of homocysteine can also affect cognition - nearly doubling the risk of developing Alzheimer’s disease in elderly people with high levels.  Long-running research called the Framington Study followed 1,092 elderly subjects without dementia over a period of eight years, and tied early high measurements of homocysteine with later development of Alzheimer’s disease and other dementias.

Normally, homocysteine is removed from the body by recycling back to methionine in a chemical reaction that requires folate and vitamin B12.  However, low levels of these vitamins make this reaction virtually impossible, resulting in high levels of homocysteine.  The 2002 report concluded that “Vitamin therapy with folic acid, alone or in combination with vitamins B6 and B12 and dietary supplementation with enriched-grain products and breakfast cereal containing folate can reduce plasma homocysteine levels.”

Interest is mounting among scientists regarding the effects of folate and vitamin B12 on the development of Alzheimer’s disease and other types of dementia. One study followed 370 elderly men and women over a period of three years, and it was determined that low serum levels of folate and vitamin B12 doubled the risks of developing Alzheimer’s disease.  Another study showed that moderate homocysteine levels and low levels of folate and vitamin B12 were linked to the presence of Alzheimer's disease and vascular dementia.
 
A 2008 meta-analysis of the effects of vitamin supplements on cognition concluded that they brought little benefit to elderly patients with confirmed dementia, but did improve cognitive function in those with high homocysteine levels who did not have dementia. A subsequent study found that vitamin supplementation did not improve cognition in people with confirmed Alzheimer's disease. This suggests that lowering homocysteine may help to prevent the development of dementia, but once the disease has developed, supplementation may no longer be helpful.

Unlike some other risk factors for disease, homocysteine levels are easy to manipulate.  Consumption of folate and vitamin B12 can all but eliminate homocysteine from the body.  Leafy, green vegetables, citrus fruit juices, legumes and fortified cereals are rich sources of folate.  Meat, poultry and fish are good sources of vitamin B12, and it can be found in milk to a lesser degree.  Vegetarians who are vegan need to obtain vitamin B12 through supplementation.

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