Recommended Dietary Allowances (RDA) of nutrients as set by the government been notoriously low. Many nutrition experts believe current RDAs are
too low and have asked for major revisions. A study in 2005 determined that many older adults need up 200 times the RDA of vitamin B12 to normalize
mild vitamin deficiency.
Individuals with AD often have low blood levels of vitamin B12. One study found lower vitamin B12 levels in the cerebrospinal fluid of patients with
AD than in patients with other types of dementia, though blood levels of vitamin B12 did not differ. Vitamin B12 deficiency, like folic acid deficiency,
leads to decreased synthesis of methionine and S-adenosyl methionine, adversely affecting methylation reactions. Methylation reactions are essential
for the metabolism of components of the myelin sheath of nerve cells as well as neurotransmitters. Also, moderately increased homocysteine levels as
well as decreased folic acid and vitamin B12 levels have been associated with AD and vascular dementia.
A study of 164 patients with AD included 76 cases in which the diagnosis was reconfirmed by examination of brain cells postmortum.
Compared to 108 control subjects without dementia, the subjects with AD had significantly higher blood homocysteine levels and lower blood levels of
both folic acid and vitamin B12.
Researchers at Boston University School of Medicine sampled 1,092 men and women without dementia and followed them for ten years to examine risk factors
for dementia. Those with higher plasma homocysteine levels at baseline had a significantly higher risk of developing AD and other types of dementia.
An Italian study of 816 elderly men and women reported that those with elevated homocysteine levels had a significantly higher risk of developing AD or
dementia.
Based on these findings, scientists have concluded that plasma homocysteine levels greater than 14 micromol per liter doubles the risk of AD. An
increased plasma homocysteine level is clearly a strong, independent risk factor for the development of dementia and AD.
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