Homocysteine, B vitamins, and Parkinson's disease
Posted 10 October 2010 - 04:05 PM
by Kathrynne Holden, MS, RD
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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Kathrynne Holden, MS
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