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Cobalamin
and Homocysteine and Cardiovascular Diseases
Evidence is mounting that an elevated
blood homocysteine level is an independent risk factor for
cardiovascular diseases (heart disease, stroke, and peripheral
vascular diseases). The amount of homocysteine in the blood
is regulated by at least three vitamins: folic acid, vitamin
B-12, and vitamin B-6 (see Diagram). Analysis of the results
of 12 homocysteine-lowering trials showed folic acid supplementation
(0.5-5 mg/day) to have the greatest lowering effect on blood
homocysteine levels (25%), with vitamin B-12 (0.5 mg/day
or 500 mcg/day) providing an additional 7% reduction (8).
However, there is evidence indicating that vitamin B-12
deficiency is a major cause of elevated homocysteine levels
in people over the age of 60. Two studies found blood methylmalonic
acid (MMA) levels to be elevated in more than 60 % of elderly
individuals with elevated homocysteine levels. An elevated
MMA level in conjunction with elevated homocysteine suggests
either a vitamin B-12 deficiency, or a combined B-12 and
folate deficiency, in the absence of impaired kidney function
(9). Thus, it is important to evaluate vitamin B-12 status
as well as kidney function in older individuals with elevated
homocysteine levels, prior to initiating homocysteine-lowering
therapy. For more information regarding homocysteine and
cardiovascular diseases see Folic Acid.
Cobalamin
and Cancer
Folate is required for synthesis of DNA
and there is evidence that decreased availability of folate
results in strands of DNA that are more susceptible to damage.
Deficiency of vitamin B-12 traps folate in a form that is
unusable by the body for DNA synthesis. Both vitamin B-12
and folate deficiencies result in a diminished capacity
for methylation reactions (see Diagram). Thus, B-12 deficiency
may lead to an elevated rate of DNA damage and altered methylation
of DNA, both of which are important risk factors for cancer.
A recent series of studies in young adults and older men
indicated that increased levels of homocysteine and decreased
levels of vitamin B-12 in the blood were associated with
a biomarker of chromosome breakage in white blood cells.
In a double-blind placebo- controlled study the same biomarker
of choromosome breakage was minimized in young adults who
were supplemented with 700 mcg of folic acid and 7 mcg of
vitamin B-12 daily in cereal for two months (10).
A recent case control study compared prediagnostic levels
of serum folate, vitamin B-6, and vitamin B-12 in 195 women
later diagnosed with breast cancer and 195 age-matched women
who were not diagnosed with breast cancer (11). Among women
who were postmenopausal at the time of blood donation, the
association between blood levels of vitamin B-12 and breast
cancer suggested a threshold effect. The risk of breast
cancer was more than doubled in those women with serum vitamin
B-12 levels in the lowest 20% (quintile) compared to those
women in the four highest quintiles. The investigators found
no relationship between breast cancer and blood levels of
vitamin B-6, folate, or homocysteine. Because this study
was observational, it cannot be determined whether decreased
blood levels of vitamin B-12 were a cause or a result of
breast cancer. Previously, there has been little evidence
to suggest a relationship between vitamin B-12 status and
breast cancer risk. However, the above studies point to
a need for further investigation of the relationship between
vitamin B-12 status and cancer risk.
Cobalamin
and Neural Tube Defects
Neural tube defects (NTD) may result
in anencephaly or spina bifida, devastating and sometimes
fatal birth defects. The defects occur between the 21st
and 27th days after conception, a time when many women do
not realize they are pregnant (12). Randomized trials have
demonstrated 60% to 100% reductions in NTD cases when women
consumed folic acid supplements in addition to a varied
diet during the month before and the month after conception
(see Folic Acid). Increasing evidence indicates that the
homocysteine-lowering effect of folic acid plays a critical
role in lowering the risk of NTD (13). Homocysteine may
accumulate in the blood when there is inadequate folate
and/or vitamin B-12 for effective functioning of the methionine
synthase enzyme (see Function). Decreased vitamin B-12 levels
in the blood and amniotic fluid of pregnant women have been
associated with an increased risk of NTD, suggesting that
adequate vitamin B-12 intake in addition to folic acid may
be beneficial in the prevention of NTD.
Cobalamin
and Alzheimer's Disease
Individuals with Alzheimer's disease
often have low blood levels of vitamin B-12. One study found
lower vitamin B-12 levels in the cerebrospinal fluid of
patients with Alzheimer's disease than in patients with
other types of dementia, though blood levels of vitamin
B-12 did not differ (14). The reason for the association
of low vitamin B-12 status with Alzheimer's disease is not
clear. Vitamin B-12 deficiency, like folate deficiency,
may lead to decreased synthesis of methionine and S-adenosylmethionine,
adversely affecting methylation reactions essential for
the metabolism of components of the myelin sheath of nerve
cells, as well as neurotransmitters. Elevated blood homocysteine
levels have been associated with Alzheimer's disease in
several studies, suggesting that homocysteine-related cerebrovascular
disease may play a role in the pathology of dementia (14).
A recent case control study of 164 patients with dementia
of Alzheimer's type included 76 cases in which the diagnosis
of Alzheimer's disease was confirmed by examination of the
brain cells after death. Compared to 108 control subjects
without evidence of dementia, subjects with dementia of
Alzheimer's type and confirmed Alzheimer's disease had higher
blood homocysteine levels and lower folate and vitamin B-12
levels (15). Measures of general nutritional status indicated
that the association of increased homocysteine levels and
diminished vitamin B-12 status with Alzheimer's disease
was not due to dementia-related malnutrition. However, clarification
of the nature of the relationship of vitamin B-12 status
to Alzheimer's disease risk will require further study before
recommendations can be made.
Cobalamin
and Depression
Observational studies have found as many
as 30% of patients hospitalized for depression to be deficient
in vitamin B-12 (16). A recent cross-sectional study of
700 community-living physically disabled women over the
age of 65 found that vitamin B-12 deficient individuals
were twice as likely to be severely depressed as non-deficient
individuals (17). The reasons for the relationship between
vitamin B-12 deficiency and depression are not clear. Vitamin
B-12 and folate are required for the synthesis of S-adenosylmethionine,
a methyl group donor essential for the metabolism of neurotransmitters,
whose bioavailability has been related to depression. Because
few studies have examined the relationship of vitamin B-12
status and the development of depression over time, it cannot
yet be determined if vitamin B-12 deficiency plays a causal
role in depression. However, due to the high prevalence
of vitamin B-12 deficiency in older individuals, it may
be beneficial to screen them for vitamin B-12 deficiency
as part of a medical evaluation for depression.
About
Cobalamin Supplements
There are number of conditions that may
cause deficiencies of vitamin B12. Individuals who suffer
from malabsorption syndrome of any cause will most likely
need extra vitamin B12. Diseases/conditions requiring supplementation
under a doctor's care include post stomach surgery, pernicious
anemia, post gastric bypass surgery, Crohn's disease, and
HIV patients with chronic diarrhea. Treatment usually involves
monthly intramuscular injections of 100 micrograms of vitamin
B12. In addition, the National academy of Sciences has recommended
that individuals over the age of 50 meet their RDA mainly
by supplement with vitamin B12.
Among all the Cobalamin Supplements,
we recommends Natural Timed B-12 1000mcg from NatureMost.
It is made in pure natural sources and in a great price
range.
Click
here for Natural Timed B-12 1000mcg from NatureMost
You may also consider taking a B-complex
vitamin or Multivitamin that contains all necessary B vitamins
to save all the trouble and avoid being overdose in particular
vitamin. We suggest the following two brand.
Click
here for Rainbow Light 40+ Complete Multivitamin
Click
here to purchase Twinlab B-Complex vitamins 100 Caps and
save!
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