General description
First discovered in the early 1940s, folic acid (also known as folate,
folacin, pteroylmonoglutamate, or vitamin B-9) is a water-soluble
vitamin that takes part in a wide variety of body processes, from
DNA synthesis to nerve signal transmission. Because it is water-soluble
and is not stored in the body, it is important to consume folic
acid every day. It may be difficult to get sufficient folic acid
from dietary sources because it is easily lost during cooking, processing,
and storage. Supplemental folic acid is usually found in the form
of a multi-vitamin or a B-complex vitamin supplement.
Food sources
The best food sources of folic acid include green leafy vegetables
like spinach and kale, whole grains, enriched grain products,
legumes, asparagus, broccoli, cabbage, and oranges.
Health applications
Functions and uses
Folic acid works together with vitamin B-12 in a variety of body
processes. Because it is required for DNA synthesis, it is crucial
for cellular division, and thus to the growth and repair of tissues.
Folic acid is critical to the development
of the fetal nervous system, and folic acid deficiency has been
linked to neural tube defects like spina bifida,1
and a variety of other birth defects.2-3 For
this reason, the U.S. Public Health Service recommends that all
women who are or may become pregnant consume 400 mcg of folic acid
per day, and the FDA now requires several enriched grain products
to include folic acid. Folic acid is involved in the production
of many neurotransmitters and is essential for healthy red blood
cells. Symptoms of folic acid deficiency include anemia, diarrhea,
irritability, weight loss, gastrointestinal disturbances, and elevated
homocysteine.
Homocysteine
Most of the health benefits provided by folic acid relate to its
role in controlling blood homocysteine levels. High
blood homocysteine levels can contribute to atherosclerosis,4
heart attack,5,6 and stroke,7
and may play a role in Alzheimer's disease 8
and other mental disorders.9 Folic acid belongs
to a group of nutrients known as "methyl donors," which help convert
homocysteine into methionine, a beneficial amino acid. Studies
have shown that folic acid supplementation can effectively reduce
plasma homocysteine levels, and that this action is enhanced by
the inclusion of vitamin B-12.10
Cancer Prevention
Among the many studies conducted on folic acid are investigations
into its potential for cancer prevention, particularly breast
and cervical cancer. While several studies have failed to show
a relationship between folic acid intake and the incidence of
cervical cancer,11,12 there is evidence that
the vitamin may reduce the excess risk of breast cancer associated
with alcohol consumption.13 Other studies
indicate that folic acid may be helpful in the prevention 14-15
and treatment 16-19 of colorectal
cancer.
Dosage/toxicity
The recommended intake for folic acid is 400 mcg per day. Higher
doses should only be used under a physician's supervision. Folic
acid is well tolerated, with no adverse side effects at this dosage.
Extremely high doses (5 to 10 mg) may cause flatulence, nausea,
and loss of appetite.20 The main concern with
folic acid supplementation is that it can mask an underlying vitamin
B-12 deficiency. Supplementing the two vitamins together is preferable
because it alleviates this concern, and because they complement
each other's activity.
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