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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.
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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.
Vitamin C for 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.
Vitamin C for 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
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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.
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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.
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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.
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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.
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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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list of all supplements, vitamins
Reviewed: 02/2006
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