Source: University of Mayland Medical Center
Also listed as: Ascorbic acid
Vitamin C is a water-soluble vitamin needed for the growth and repair
of tissues in all parts of the body. It is necessary to form collagen,
an important protein used to make skin, scar tissue, tendons,
ligaments, and blood vessels. Vitamin C is essential for the healing of
wounds, and for the repair and maintenance of cartilage, bones, and
teeth.
Vitamin C is one of many antioxidants. Vitamin E and beta-carotene are
two other well known antioxidants. Antioxidants are nutrients that
block some of the damage caused by free radicals, which are by-products
that result when our bodies transform food into energy. The build up of
these by-products over time is largely responsible for the aging
process and can contribute to the development of various health
conditions such as cancer, heart disease, and a host of inflammatory
conditions like arthritis. Antioxidants also help reduce the damage to
the body caused by toxic chemicals and pollutants such as cigarette
smoke.
Vitamin C deficiency can lead to dry and splitting hair; gingivitis
(inflammation of the gums) and bleeding gums; rough, dry, scaly skin;
decreased wound-healing rate, easy bruising; nosebleeds; weakened
enamel of the teeth; swollen and painful joints; anemia; decreased
ability to ward off infection; and, possibly, weight gain because of
slowed metabolic rate and energy expenditure. A severe form of vitamin
C deficiency is known as scurvy, which mainly affects older,
malnourished adults.
The body does not manufacture vitamin C on its own, nor does it
store it. It is therefore important to include plenty of vitamin
C-containing foods in one's daily diet. Large amounts of vitamin C are
used by the body during any kind of healing process, whether it's from
an infection, disease, injury, or surgery. In these cases extra vitamin
C may be needed.
Low levels of vitamin C have been associated with a variety of
conditions including hypertension, gallbladder disease, stroke, some
cancers, and atherosclerosis (the build up of plaque in blood vessels
that can lead to heart attack and stroke; conditions that are caused by
atherosclerotic build up are often collectively referred to as
cardiovascular diseases). Eating adequate amounts of vitamin C in the
diet (primarily through lots of fresh fruits and vegetables) may help
reduce the risk of developing some of these conditions. There is little
evidence, however, that vitamin C supplements can cure any of these
diseases.
As an anti-oxidant, vitamin C plays an important role in protecting against the following:
Heart Disease
Results of scientific studies regarding the benefit of vitamin C
for heart disease or stroke is somewhat confusing. While not all of the
studies agree, some information suggests that vitamin C may help
protect blood vessels from the damaging effects that lead to or result
from the presence of atherosclerosis.
For example, those with low levels of vitamin C may be more likely to
have a heart attack, stroke, or peripheral artery disease, all
potential outcomes of atherosclerosis. Peripheral artery disease is the
term used to describe atherosclerosis of the blood vessels to the legs.
This can lead to pain with walking, known as intermittent claudication.
In terms of damage that can cause atherosclerosis, some studies have
shown that vitamin C helps prevent oxidation of LDL (bad) cholesterol –
a process that contributes to plaque buildup in the arteries.
Under most circumstances, dietary vitamin C is adequate for protecting
against the development of or consequences from cardiovascular disease.
If you have low levels of this nutrient, however, and find it difficult
to obtain through dietary sources, a knowledgeable healthcare provider
may recommend vitamin C supplements.
High Cholesterol
Information from several studies, involving only small numbers of
people, suggest that vitamin C (3 glasses of orange juice per day or up
to 2000 mg per day as a supplement) may help decrease total and LDL
cholesterol and triglycerides, as well as increase HDL levels (the good
kind of cholesterol). Studies evaluating larger groups of people would
be helpful in determining how accurate these preliminary research
results are and to whom this potential benefit applies.
High Blood Pressure
Free radicals, the damaging by-products of metabolism mentioned
earlier, are associated with higher blood pressure in studies of
animals and people. Population based studies (which involve observing
large groups of people over time) suggest that people who eat foods
rich in antioxidants, including vitamin C, are less prone to high blood
pressure than people without these nutritious foods in their diet. For
this reason, many clinicians recommend foods rich in vitamin C,
particularly if you are at risk for high blood pressure. In fact, the
diet most frequently recommended for treatment and prevention of
hypertension, known as the DASH (Dietary Approaches to Stop
Hypertension) diet advocates lots of fruits and vegetables, which are
loaded with antioxidants.
Common Cold
Despite the popular belief that vitamin C can cure the common cold,
the scientific evidence supporting this conviction is limited. There
have been a few studies suggesting that taking large doses of vitamin C
supplements at the onset of cold or flu symptoms, or just after
exposure to one of these viruses, can shorten the duration of the cold
or ward it off altogether. However, the majority of studies, when
looked at collectively, lead researchers to conclude that vitamin C
does not prevent or treat the common cold. Some experts suggest that
vitamin C may only be useful in case of a cold if you have low levels
of this nutrient to begin with. Another possibility is that the
likelihood of success may be very individual – some improve, while
others do not. If you are amongst the 67% of people who believe that
vitamin C is helpful for your colds, there may be power in your
conviction. In other words, your experience is probably more important
than what the research is stating. Talk to your doctor about any pros
and cons with regards to using vitamin C during cold and flu season.
Cancer
While the precise role of vitamin C in preventing cancer remains
controversial, results of many population based studies (evaluating
groups of people over time) imply that foods rich in vitamin C may be
associated with lower rates of cancer, including skin cancer, cervical
dysplasia (changes to the cervix which may be cancerous or
precancerous, picked up by pap smear), and, possibly, breast cancer. At
best, however, particularly for breast cancer, the specific connection
of vitamin C and cancer prevention is weak. This is mainly because
protection comes from eating foods, such as fruits and vegetables,
which contain many beneficial nutrients and antioxidants, not only
vitamin C.
Also, there is no evidence that taking large doses of vitamin C once
diagnosed with cancer will help your treatment. In fact, there is
concern that large doses of antioxidants from supplements could
interfere with chemotherapy medications. Much more research in the area
of antioxidants and cancer treatment is needed.
Osteoarthritis
Vitamin C is essential for normal cartilage. Plus, free radicals can be
produced in the joints and have been implicated in many degenerative
changes in the aging body, including destruction of cartilage and
connective tissue that lead to arthritis. Antioxidants appear to offset
the damage caused by free radicals. Although further evidence is needed
to substantiate these claims, studies of groups of people observed over
time suggest that vitamin C, as well as vitamin E, may help to reduce
the symptoms of OA.
Obesity and Weight Loss
Studies suggest that obese individuals may have lower vitamin C
levels than nonobese individuals. Researchers speculate that
insufficient amounts of vitamin C may contribute to weight gain by
decreasing metabolic rates and energy expenditures. Many sensible
weight loss programs will be sure to include foods rich in vitamin C,
such as plenty of fruits and vegetables.
Cataracts
Studies have shown that vitamin C may slow or even stop the progression
of cataracts in the elderly. A recent study, for example, of women from
the Nurses' Health Study (a very large, important study that has
followed women over many years) showed that women under 60 years of age
who had high dietary intake of vitamin C or who had used vitamin C
supplements for 10 years or more had significantly reduced chances of
developing cataracts.
Age-related Macular Degeneration
Vitamin C works together with other antioxidants like selenium,
beta-carotene, and vitamin E to protect the eyes against developing
macular degeneration. This is a painless, degenerative eye disease that
affects more than 10 million Americans. It is the leading cause of
legal blindness in persons over the age of 55 in the United States.
While complete blindness does not occur in most people with the
disorder, macular degeneration often interferes with reading, driving,
or performing other daily activities.
While not all research agrees, antioxidants, including vitamin C,
primarily from dietary sources may help prevent macular degeneration.
Many qualified clinicians will recommend a combination of these
nutrients for treating or preventing this serious and frustrating eye
disorder.
Diabetes
Vitamin C may be helpful for people with diabetes in a number of
ways. First, some studies suggest that people with diabetes have high
levels of free radicals (the damaging metabolic by-products, mentioned
earlier, associated with many chronic illnesses) and low levels of
antioxidants, including vitamin C. This imbalance may contribute to the
fact that those with diabetes are at greater risk for developing
conditions such as high cholesterol and atherosclerosis.
Secondly, insulin (which is low in type 1 diabetics and does not
function properly in type 2 diabetics) helps cells in the body take up
the vitamin C that they need to function properly. At the same time,
lots of circulating blood sugar (glucose), as is often the present in
diabetics, prevents the cells from getting the vitamin C that they
need, even if eating lots of fruits of vegetables. For this reason,
taking extra vitamin C in the form of supplements may be helpful in
those with diabetes.
Alzheimer's Disease and other types of Dementia
While the evidence is somewhat stronger for another important
antioxidant, namely vitamin E, vitamin C may help prevent the
development of Alzheimer's disease. It may also improve cognitive
function in dementia from causes other than Alzheimer's (such as
multiple strokes). The use of these antioxidants for improving
cognitive ability in those who already have dementia of the Alzheimer's
type has not been well tested to date.
Other
Although the information is somewhat limited, studies suggest that vitamin C may also be helpful for:
- Boosting immune system function
- Maintaining healthy gums
- Relieving eye pressure in those with glaucoma
- Improving visual clarity for those with uveitis (an inflammation of the middle part of the eye)
- Slowing progression of Parkinson's disease
- Treating allergy-related conditions, such as asthma, eczema, and hay fever (called allergic rhinitis)
- Relieving pain from pancreatitis; vitamin C levels are often low with this condition
- Reducing effects of sun exposure, such as sunburn or redness (called erythema) and even, possibly, skin cancer
- Alleviating dry mouth, particularly from antidepresant medications (a common side effect from these drugs)
- Healing burns and wounds
Since vitamin C is not produced by the body, it must be obtained from
fruits and vegetables. Some excellent sources of vitamin C are oranges,
green peppers, watermelon, papaya, grapefruit, cantaloupe,
strawberries, kiwi, mango, broccoli, tomatoes, brussels sprouts,
cauliflower, cabbage, and citrus juices or juices fortified with
Vitamin C. Raw and cooked leafy greens (turnip greens, spinach), red
and green peppers, canned and fresh tomatoes, potatoes, winter squash,
raspberries, blueberries, cranberries and pineapple are also rich
sources of Vitamin C. Vitamin C is sensitive to light, air, and heat,
so it is best to eat fruits and vegetables raw, or minimally cooked in
order to retain their full vitamin C content.
You can purchase either natural or synthetic vitamin C, also called
ascorbic acid, in a wide variety of forms. Tablets, capsules, and
chewables are probably the most popular, but vitamin C also comes in
powdered crystalline, effervescent, and liquid forms. Vitamin C can be
purchased in dosages ranging from 25 mg to 1,000 mg.
"Buffered" vitamin C is also available if you find that regular
ascorbic acid upsets your stomach. An esterified form of vitamin C is
also available, which tends to be better tolerated by people who are
prone to heartburn or have a sensitive stomach.
Some vitamin C supplements contain bioflavonoids, which appear to enhance absorption and utilization of ascorbic acid.
There is concern about tooth enamel erosion occurring from the acid content of chewable vitamin C.
Vitamin C is not stored in the body, so it must be replaced as it gets
used. The best way to take supplements is with meals two or three times
per day, depending on the dosage. Some studies suggest that adults
should take between 250 mg and 500 mg twice a day for maximum benefit.
A knowledgeable healthcare provider should be consulted before taking
more than 1,000 mg of vitamin C on a daily basis and before giving
vitamin C to a child.
Daily intake of dietary vitamin C (according to the U.S. RDA), are listed below.
Pediatric
- Neonates 1 to 6 months: 30 mg
- Infants 6 to 12 months: 35 mg
- Children 1 to 3 years: 40 mg
- Children 4 to 6 years: 45 mg
- Children 7 to 10 years: 45 mg
- Children 11 to 14 years: 50 mg
- Adolescent girls 15 to18 years: 65 mg
- Adolescent boys 15 to18 years: 75 mg
Adult
- Men over 18 years: 90 mg
- Women over 18 years: 75 mg
- Breastfeeding women: first 6 months: 95 mg
- Breastfeeding women: second 6 months: 90 mg
Because smoking depletes vitamin C, people who smoke generally need an additional 35 mg/day.
The doses recommended to prevent or to treat many of the conditions
mentioned in the Uses section is often between 500 and 1,000 mg per
day.
Because of the potential for side effects and interactions with
medications, dietary supplements should be taken only under the
supervision of a knowledgeable healthcare provider.
It is important to drink plenty of fluids when taking supplemental vitamin C because it has a diuretic effect.
Most commercially available vitamin C is derived from corn. People
sensitive to corn should look for alternative sources, such as sago
palm.
Vitamin C increases the amount of iron absorbed from foods. This may
be helpful for people who have low blood iron levels. However, people
with hemochromatosis should not take vitamin C supplements because of
enhanced accumulation of non-heme iron in the presence of this vitamin.
During periods of stress (either emotional or physical), urinary
excretion of vitamin C is increased. Extra vitamin C through vitamin C
rich foods as well as supplements is often recommended to keep the
immune system working properly during these times.
While vitamin C is generally non-toxic, in high doses (more than 2,000
mg daily) it can cause diarrhea, gas, or stomach upset. Those who have
kidney problems should check with a healthcare provider before taking
vitamin C supplements. Infants born to mothers taking 6,000 mg or more
of vitamin C may develop rebound scurvy due to a sudden drop in daily
intake. As described earlier, scurvy is a condition caused by extreme
vitamin C deficiency. See earlier explanation for the possible symptoms
of vitamin C deficiency.
If you are currently being treated with any of the following
medications, you should not use vitamin C supplements without first
talking to your healthcare provider.
Aspirin and Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)
Very limited research suggests that vitamin C may protect the
stomach and intestines against injury from NSAIDs such as ibuoprofen.
On the other hand, high doses of vitamin C (equal to or greater than
500 mg per day) may raise the blood levels of aspirin and other acidic
medications.
Acetominophen
Vitamin C may decrease excretion of acetaminophen (a medication sold
over the counter for pain and headache) in the urine, which may
increase blood levels of this medication.
Diuretics, Loop
Animal studies suggest that vitamin C may amplify the effects of
furosemide, which belongs to a class of medications known as loop
diuretics.
Beta-blockers for high blood pressure
Vitamin C may decrease the absorption of propranolol, a medication that
belongs to a class known as beta-blockers used for high blood pressure
and other heart-related conditions. If taking vitamin C and a
beta-blocker, therefore, it is best to take them at different times of
the day.
Cyclosporine
Cyclosporine, a medication used for the treatment of cancer, may reduce blood levels of vitamin C.
Nitrate Medications for heart disease
The combination of vitamin C with nitroglycerin, isosorbide
dinitrate, or isosorbide mononitrate reduces the occurrence of nitrate
tolerance. Nitrate tolerance is when the body builds up a tolerance to
the medicine so that it no longer has its desired effect. People taking
nitrate-containing medications generally follow a 12 hours on, 12 hours
off schedule to avoid this tolerance. Studies suggest that taking
vitamin C along with nitrate medications may reduce the development of
this tolerance.
Tetracycline
There is some evidence that taking vitamin C with the antibiotic tetracycline may increase the levels of this medication.
Warfarin
There have been rare case reports of vitamin C interfering with the
effectiveness of this blood thinning medication. In recent follow up
studies, no such association has been found with doses of vitamin C up
to 1,000 mg per day. Because of these much earlier reports, however,
some conservative clinicians suggest not exceeding RDA values of
vitamin C (see earlier section entitled How To Take It). Whether taking
recommended dietary amounts or larger quantities of vitamin C, anyone
on warfarin must have their bleeding time measured regularly and
followed closely using a value called an INR, measured at your doctor's
office. If you take this blood thinner, any time you make a change to
your diet, medications, or supplements, you must notify your physician.
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- Review Date:
4/1/2002
- Reviewed By: Participants in the review process include:
Jacqueline A. Hart, MD, Department of Internal Medicine,
Newton-Wellesley Hospital, Harvard University and Senior Medical Editor
Integrative Medicine, Boston, MA; Gary Kracoff, RPh (Pediatric Dosing
section February 2001), Johnson Drugs, Natick, Ma; Steven Ottariono,
RPh (Pediatric Dosing section February 2001), Veteran's Administrative
Hospital, Londonderry, NH; Margie Ullmann-Weil, MS, RD, specializing in
combination of complementary and traditional nutritional therapy,
Boston, MA. All interaction sections have also been reviewed by a team
of experts including Joseph Lamb, MD (July 2000), The Integrative
Medicine Works, Alexandria, VA;Enrico Liva, ND, RPh (August 2000),
Vital Nutrients, Middletown, CT; Brian T Sanderoff, PD, BS in Pharmacy
(March 2000), Clinical Assistant Professor, University of Mayland
School of Pharmacy; President, Your Prescription for Health, Owings
Mills, MD; Ira Zunin, MD, MPH, MBA (July 2000), President and Chairman,
Hawaii State Consortium for Integrative Medicine, Honolulu, HI.
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