Cardiovascular
disease
The evidence from epidemiological studies, animal
experiments and some clinical trials suggests that vitamin C supplements
may protect against the development of cardiovascular disease. In the
same study mentioned in the previous paragraph, those taking vitamin
E supplements had a 47 per cent lower risk of death from heart disease
and those taking both vitamin C and vitamin E had a 53 per cent reduced
risk.34
Vitamin C may exert
its protective effects by lowering total blood cholesterol and harmful
LDL cholesterol and raising beneficial HDL cholesterol. Vitamin C also
increases the production of prostacyclin, a prostaglandin which decreases
the clumping of blood platelets and dilates blood vessels, therefore
reducing the risk of heart disease, atherosclerosis and stroke.
High fat meals cause
damage to artery linings, which may contribute to the development of
atherosclerosis. Research published in 1997 suggests that taking the
antioxidant vitamins C and E before a meal may help to prevent this
damage. The study which was carried out at the University of Maryland
School of Medicine involved 13 women and seven men with normal blood
cholesterol levels. Once a week for three weeks, the subjects ate either
a high fat meal, a low fat meal, a high fat meal after taking 1000 mg
of vitamin C and 800 IU of vitamin E, or a low fat meal after taking
the antioxidants. Before and after the meals, the researchers measured
blood fat and cholesterol levels, blood pressure and heart rate in the
subjects. They also used ultrasound to measure the dilation of an artery
in the arm after release of a tourniquet which had been applied for
five minutes. If the artery lining is functioning normally, it releases
nitric oxide which causes dilation. The results showed that the high
fat meal decreased artery lining function for up to four hours afterwards,
whereas the low fat meal did not. This is probably due to oxidative
stress caused by an accumulation of triglyceride-rich lipoproteins (blood
fats). Vitamins C and E prevented this decrease in artery lining function.35
A recent US study
looked at the effect of either 2 g of vitamin C or a placebo on patients
with coronary artery disease. In such patients the arteries leading
to the heart are unable to open when the heart requires increased blood
flow. Those patients given the vitamin C experienced expansion in their
arteries while those given the placebo experienced no effect.36
Vitamin C has similar effects in those with high cholesterol37
and in those with chronic heart failure.38
When blood is re-supplied
to an organ from which it was previously cut off, oxidative damage can
occur. This has been found in many types of surgery, for example in
heart bypass operations. Vitamin C has also been shown to protect against
this reperfusion injury.39
Smoking
Vitamin C needs are higher in smokers and several
studies suggest that vitamin C may protect against smoking-related damage.
It may help to decrease the smoking-related build-up of atherosclerotic
plaque by limiting the amount of white blood cells that stick to artery
walls.40 Vitamin C supplements
may be helpful in restoring reduced plasma vitamin C concentrations
in smokers.41 Like those
with high cholesterol levels and coronary heart disease, the arteries
of smokers have a reduced ability to dilate. Vitamin C supplements may
counteract this impairment.42
High
blood pressure
Vitamin C may also be of benefit in the treatment
of mild high blood pressure, another risk factor for heart disease and
stroke. Some research suggests that vitamin C may have beneficial effects
in lowering high blood pressure.43
Vitamin C supplements improve abnormal artery lining function in hypertensive
people.44
Cancer
prevention
Vitamin C supplements may have a part to play in
cancer prevention. Some research suggests that the risk of cancer is
lower in those taking supplements. Vitamin C may exert its anticancer
effects by acting as an antioxidant and shielding the genetic mechanism
of the cell from damage that can lead to cancerous changes. Vitamin
C may also strengthen the ability of the immune system to track down
and destroy pre-cancerous cells. Vitamin C may exert its protective
effects against some cancers by inhibiting the formation of toxic compounds
known as nitrosamines from nitrite food additives. These compounds are
also found in cigarette smoke and are linked to an increased risk of
stomach and lung cancers.
Stomach
cancer
Supplements may be useful in helping to prevent
stomach cancer. In a 1996 study, researchers gave 32 patients 500 mg
of vitamin C twice daily for two weeks. Levels in gastric juices and
gut tissues were increased, raising the possibility of increased protection
against free radicals.45
A 1997 report in
the journal, Cancer, suggests that vitamin C may inhibit the growth
of Helicobacter pylori, a stomach bacterium that increases the risk
of ulcers and stomach cancer. High concentrations of vitamin C inhibited
the growth of bacteria in culture dishes and also in the stomachs of
Mongolian gerbils, according to researchers at the International Medical
Center of Japan in Tokyo. Vitamin C-rich diets have been found to decrease
the risk of stomach cancer. This has been attributed to the antioxidant
ability of vitamin C. However, vitamin E, which is also an antioxidant,
does not inhibit the growth of Helicobacter pylori. This suggests that
vitamin C may exert its protective effects through a biochemical mechanism.
This research suggests the possibility of a safe, side effect-free alternative
to antibiotics for the treatment of ulcers.46
Colon
cancer
Vitamin C supplements have also been shown to have
beneficial effects against the pre-cancerous changes which occur in
colon cancer. In a 1992 study, 20 patients with colorectal cancer were
given vitamins A, C, and E for six months and 21 patients with adenomas
received placebo. The results showed that supplementation with vitamins
A, C, and E was effective in reducing pre-cancerous abnormalities.47
Vitamin C supplements may also be beneficial in the treatment of prostate
cancer.48
Cancer
treatment
Controversy surrounds the use of vitamin C in the
treatment of cancer. The Nobel Prize winner, Linus Pauling and his colleagues
have used vitamin C to improve survival times in cancer patients, but
these results have not been repeated in other studies. Vitamin C may
also benefit cancer patients who are undergoing radiation treatment
by enabling them to withstand greater doses of radiation with fewer
side effects.49
Asthma
and allergy
There is some evidence that vitamin C is of benefit
in reducing the bronchial constriction and impaired breathing seen in
asthma and allergic responses. This effect may be due to the antioxidant
effect of vitamin C as oxidizing agents promote inflammation and can
increase allergic responses. Vitamin C may also improve lung and white
blood cell function and decrease respiratory infections and hypersensitivity
reactions by reducing histamine levels. However, some studies do not
support a beneficial role in vitamin C in asthma. Most studies have
been short term and have assessed immediate effects of vitamin C supplementation.
The effect of long-term supplementation with vitamin C is unclear.50
According to researchers
from the University of Washington, antioxidant vitamin supplements may
help relieve the symptoms of asthma. The researchers measured the amount
of breath expelled by the lungs in 17 asthma sufferers. The subjects
took peak flow lung function tests while running on a treadmill and
breathing in high levels of polluted air. In those asthmatics whose
diets were supplemented with daily doses of 400 IU of vitamin E and
500 mg of vitamin C, an 18 per cent increase in peak flow capacity was
seen.
In a 1997 study,
20 asthma patients underwent lung function tests at rest, before and
one hour after receiving 2 g of oral ascorbic acid. They were then randomly
assigned in a double-blind manner to receive 2 g of ascorbic acid or
a placebo one hour before a 7-minute exercise session on a treadmill.
Lung function tests were performed after an 8-minute rest. This procedure
was repeated one week later, with each patient receiving the alternative
medication. In nine patients, a protective effect on exercise-induced
hyperreactive airways was seen.51
Immunity
Vitamin C boosts immunity by increasing the production
of B and T cells and other white blood cells, including those that destroy
foreign micro-organisms. It also increases interferon levels and antibody
responses and has antiviral and antibacterial effects. These effects
lead to improved resistance against infections.
Vitamin C has been
shown to help the immune system recover from exposure to toxic chemicals.
In a 1997 study, researchers studied the effect of vitamin C on the
function of several immune cells (natural killer, T and B cells) in
patients who had been exposed to toxic chemicals. Fifty-five patients
were given buffered vitamin C in water at a dosage of 60 mg per kg body
weight (around 4g for the average man). Twenty-four hours later, the
researchers tested immune cell function. The results showed that natural
killer cell activity was enhanced up to ten-fold in 78 per cent of patients.
B and T cell function was restored to normal.52
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HIV
/ AIDS
Vitamin C supplements are likely to be useful in
HIV-positive individuals as they have been shown to boost the immune
system and prevent damage to nerves. However, caution should be used
with very high doses as they can cause diarrhea. Vitamin C has been
shown to inhibit HIV in the laboratory and may also kill HIV-infected
cells.53
Common
cold
Vitamin C may reduce the duration of the common
cold and also the severity of symptoms such as sneezing, coughing and
sniffling. Its use as a cold treatment is controversial but it seems
to have several effects, including reducing blood levels of histamine
which can trigger tissue inflammation and a runny nose. It may also
protect the immune cells and surrounding tissue from damaging oxidative
reactions that occur when cells fight bacteria.54
It is possible
that the effects of supplementation are greater in those with low dietary
vitamin C intake. In general, men have lower vitamin C levels than women.
In four studies with British girls and women, vitamin C supplementation
had no marked effect on common cold. However, in four studies involving
British male schoolchildren and students, a reduction in common cold
occurrence was found in groups supplemented with vitamin C.55
Research suggests
that vitamin C supplementation may be beneficial for people who do heavy
exercise and who have problems with frequent upper respiratory tract
infections. Three placebo-controlled studies have examined the effect
of vitamin C supplementation on common cold occurrence in people under
acute physical stress. In one study the subjects were school children
at a skiing camp in the Swiss Alps; in another they were military troops
training in Northern Canada; and in the third they were participants
in a 90 km running race. In each of the three studies, a considerable
reduction in common cold incidence in the group supplemented with vitamin
C at levels of 600 mg to 1000 mg per day was seen.56
Cataracts
Many studies show that vitamin C can protect against
cataracts, possibly by reducing oxidative damage caused by ultraviolet
light. Vitamin C may act to protect the lens of the eye from this damage
and protect enzymes within the lens that remove oxidation damaged proteins.
In a study published
in 1992, researchers at Harvard Medical School examined the link between
dietary intake of vitamins C and E, carotene, and riboflavin and cataract
extraction in over 50 000 women taking part in the Nurses Health Study.
The results showed that the risk of cataract was 45 per cent lower among
women who used vitamin C supplements for ten or more years.57
Further results
from this study reported in 1997 in the American Journal of Clinical
Nutrition also suggests that vitamin C supplements taken for long periods
can reduce the development of cataracts. Researchers from the US Department
of Agriculture and Harvard School of Public Health examined the link
between cataract development and vitamin C supplement use over a ten
to 12 year period. The subjects were 247 Boston area nurses aged from
56 to 71. The researchers performed detailed eye examinations to determine
the degree of opacity (clouding) of the lenses of the eyes of the subjects.
Results showed that use of vitamin C supplements for over ten years
was associated with a 77 per cent lower prevalence of early lens opacities
and an 83 per cent lower prevalence of moderate lens opacities.58
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Diabetes
Increasing vitamin C intake may improve blood sugar
regulation in diabetics. Vitamin C administration in pharmacological
doses for four months in Type II diabetes has been shown to have beneficial
effects on glucose and lipid metabolism, blood circulation and capillary
fragility.
In a 1995 study
the effect of magnesium and vitamin C supplements on metabolic control
was assessed in 56 diabetics. The study involved a 90-day run-in period
followed by two 90-day treatment periods, during which patients received
600 mg of magnesium and 2 g of vitamin C per day. The results showed
that vitamin C supplementation improved glycemic control, fasting blood
glucose, cholesterol and triglyceride levels.59
High blood sugar
levels in diabetes cause a compound known as sorbitol to be manufactured
from glucose. This contributes to the progression of diabetic complications.
Vitamin C has been shown to reduce levels of sorbitol in diabetics.
In a 58-day study carried out in 1994, researchers investigated the
effect of two different doses of vitamin C supplements (100 or 600 mg)
on young adults with Type I diabetes. The results showed that vitamin
C supplementation at either dose normalized sorbitol levels in those
with diabetes in 30 days.60
Vitamin C may also help to reduce capillary fragility, which also contributes
to complications. The ability of the arteries to dilate is impaired
in diabetics. Vitamin C supplements improve the response.61
Skin
protection
Vitamins C and E taken together may protect against
sunburn. In a study published in 1998, German dermatologists found that
people who took these vitamins had a higher threshold for sunburn reaction.
The researchers tested ultraviolet sensitivity in two groups of ten
Caucasian people by exposing a section of skin to UV light. Subjects
in one of the groups then took 2 g of vitamin C and 1000 IU of vitamin
E for eight days. The UV test was then re-done. Those taking the vitamins
showed increased tolerance, particularly at higher UV doses. However,
in comparison with the protection afforded by topical sunscreens, this
level of protection is small.62
Vitamin C-containing
cosmetic skin creams such as Cellex-C have also become extremely popular
in the last few years. They are designed to protect against pollutants
and to promote healing.
Gallstones
Vitamin C is involved in cholesterol metabolism
and deficiency may increase the risk of gallstones. In a 1998 study
published in the Journal of Clinical Epidemiology, researchers in San
Francisco found that vitamin C supplements reduced the prevalence of
gall bladder disease by half in 2744 postmenopausal women who regularly
drank alcohol. Supplement use was also associated with a 62 per cent
decrease in gallstone removal. The supplements had no effect on those
who did not drink.63
Researchers involved
in a 1997 study to test the effect of vitamin C supplements on gallstones
analyzed blood fat levels, cholesterol metabolism, bile fat composition
and cholesterol saturation in 16 gallstone patients. They then treated
the patients with 500 mg of vitamin C four times a day for two weeks
before surgery. Their findings indicated that vitamin C supplementation
may also influence the conditions for cholesterol gallstone formation.64
Exercise
Strenuous exercise appears to increase the levels
of free radicals in the body, increasing the risk of disorders in which
oxidative damage plays a part. As an antioxidant, vitamin C may help
to prevent this damage. In a 1997 study, researchers examined the effects
of supplements on oxidative stress in athletes. They found that exercise-induced
oxidative stress was highest when those involved in the study did not
supplement with vitamin C.65
Other
uses
Vitamin C has also been used to treat constipation
and to speed wound healing. Recent research suggests that vitamin C
may help to enhance the strength of sperm in smokers.66
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