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Homocysteine, B vitamins, and Parkinson's disease

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Homocysteine, B vitamins, and Parkinson's disease

by Kathrynne Holden, MS, RD

Copyright 2008-2010


What is homocysteine?


Homocysteine is an amino acid found in the bloodstream; it is naturally

produced in small amounts by the human body from its precursor,

methionine. The body also removes homocysteine from the blood, using the B

vitamins folate, B12, and B6. An amount of homocysteine between 5 and 15

micromoles per liter of blood is considered normal; amounts greater than

that are considered "hyperhomocysteinemia" or elevated homocysteine.


Why is elevated homocysteine a problem?


The relationship between homocysteine and diseases is not clearly

understood at this time. However, researchers have discovered that

homocysteine can prevent the formation of nitric oxide, a substance that

keeps blood vessels pliable and prevents formation of atherosclerosis.

Thus, homocysteine could be implicated in cardiovascular disease, strokes,

and heart attacks.


Homocysteine may also be associated with memory impairment. In a study of

elderly individuals, elevated homocysteine was associated with cognitive

impairment (poorer ability to read, learn, remember, and understand) while

high levels of folate and vitamin B12 were associated with improved

cognition. Other researchers studied 1092 people aged 68 to 97, and found

that those whose homocysteine levels were over 14 micromoles per liter had

twice the risk of developing Alzheimer's disease as those with lower



The findings are based on a study of 1,092 people from

68 to 97 who were initially healthy and free of dementia. Their

homocysteine levels were measured and their health was monitored for

eight years. At the end of the study, 111 individuals had dementia,

including 83 with Alzheimer's. People whose homocysteine levels were

higher than 14 micromoles per liter of blood, one- fourth of the

participants, had nearly twice the Alzheimer's risk of those with lower



What about people with Parkinson's disease?


Some scientists found that people with PD who had been using levodopa for

some time had higher levels of homocysteine than newly-diagnosed PD

patients who had not begun treatment with levodopa. In another study,

using mice, researchers found that on a low-folate diet the mice had

increased levels of homocysteine. They speculate that increased

homocysteine can worsen oxidative stress on the neurons that produce

dopamine, and make them more easily damaged by environmental toxins.


Some degree of cognitive impairment, ranging from mild memory loss to

various types of dementias, is common among people with PD, more so than

in the general population. While not all cognitive impairment is related

to nutrient deficiency, some cases may well be, especially as people with

PD often change their eating habits in unsatisfactory ways.


In an article "Homocysteine and Atherosclerotic Heart Disease: A New and

'Unusual Suspect,'" Michelle Taylor-Chinn writes:


..... clinicians are advised to assess fasting homocysteine levels only

in high-risk patients -- including those with arterial occlusive disease,

hypothyroidism, impaired kidney function, systemic lupus erythematosus, or

a significant family history of premature atherosclerosis. Elderly

patients should also be considered for testing, as should patients who

receive certain medications or therapy (eg, theophylline, methotrexate,

levodopa, niacin [vitamin B3], nitrous oxide exposure). [Clinician Reviews

10(10):45-57, 2000. © 2000 Clinicians Publishing Group]


Because many people with PD meet one or more of these risk factors

(i.e., age, use of levodopa, and possibly other conditions), I recommend

that you discuss testing for homocysteine with your physician. Older

people in particular may not absorb vitamin B12 sufficiently from food,

and should be assessed for possible deficiency. I also advise an eating

pattern that includes vegetables, whole-grain and fortified breads and

cereals, fruits, dried beans, peas, and lentils, and fish.


-- Kathrynne Holden, MS, RD



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