The idea that vitamin C supplementation might be of benefit against colds achieved wide popularity in the 1970s.
This is because the well-known chemist and Nobel prize winner Linus Pauling wrote a best-selling book titled ‘Vitamin C and the Common Cold’.
Whether or not vitamin C helps prevent or cure the common cold is a matter of great controversy.
The thing is: some studies that showed an effect are criticized because they were not designed and performed according to the basic rules of well-conducted scientific research.
And you should also realize that duration and severity of cold symptoms are extremely difficult topics to investigate and measure.
So what are the latest scientific insights?.
After reviewing almost 60 years of research, it was reported in 2012 that vitamin C does not prevent you from getting the cold.
When taken after a cold starts, vitamin C supplements do not make a cold shorter or less severe.
But when already taken daily, vitamin C very slightly shorted cold duration: by around 8% in adults and by 14% in children.
So what does all this mean?
According to this research, the average adult who suffers with a cold for 12 days a year, would still suffer for about 11 days if that person took a high dose of vitamin C every day during that year.
For the average child who suffers about 28 days of cold illness a year, taking a high dose of vitamin C each day would still likely mean about 24 days of cold illness.
When vitamin C was tested for treatment of colds in 7 studies, it was found to be no more effective than placebo at shortening the duration of cold symptoms.
The severity of cold symptoms were reported to be slightly less when vitamin C was taken before a cold started.
This may be because of the antioxidant actions of vitamin C against the oxidizing agents produced by, and released from, the activated immune cells – thus a decreased inflammatory response.
A stuffy nose also develops in response to elevated blood histamine, and people commonly take anti-histamines for relief.
Vitamin C can also deactivate histamine, relieving the symptoms of a stuffy nose.
Vitamin C from foods and supplements has also been investigated for prevention of cancer, heart disease, stroke, and age-related eye disease.
Results were conflicting and often disappointing.
In studies where groups of people were compared, vitamin C consumption from both food and supplements correlated with reduced death and incidence of heart disease, especially when subjects had low intakes of vitamin C.
In one study, in which vitamin C or a placebo were given, it was found that vitamins C and E slowed the progression of plaque formation, but a protective effect for plaque formation was not observed by investigators in other studies.
In large-scale intervention studies, when vitamin C was partially obtained from foods but was also consumed in combination with other antioxidant vitamins, no benefit in preventing cancer or reducing vascular disease was observed.
Cataract is a disease of ageing people in which the lens of the eye becomes cloudy and you cannot see well.
Oxidative stress might contribute to the cause of cataract.
Observational data have indicated that vitamin C supplementation may prevent cataract, but a large prospective study showed no effect when vitamin C supplements were combined with vitamin E and beta-carotene.
Vitamin C supplementation was also tested for hypertension, blood vessel dysfunction, and respiratory diseases.
Investigators noted a modest effect on lowering blood pressure in some but not all subjects, and no large-scale studies are available.
Blood vessel function was slightly improved when vitamin C was injected directly in the artery, but the question still remains whether this can also be achieved when vitamin C is given orally.
Vitamin supplements probably do not prevent acute respiratory infections in healthy people, nor do they provide benefit in asthma treatment.
Vitamin C can potentially inactivate free radicals in the stomach and small intestine; it can prevent formation of potentially damaging compounds such as nitrosamines.
Whether this has clinical benefit is controversial.
Intake of foods high in vitamin C usually correlates with a reduced risk of gastric cancer; it is unknown whether vitamin C itself or other substances in vitamin C–rich plant-derived foods are responsible.
In the small intestine, vitamin C promotes iron absorption.
A dose of vitamin C that is found in vitamin C–rich foods, enhanced the uptake of iron up to ten times more, depending on iron status, vitamin C dose, and test meal type.
The effect of vitamin C on raising hemoglobin concentration was modest.
In clinical practice, vitamin C is given with iron to increase its absorption, especially in pregnancy.
Thus, taken together, conclusive evidence that a particular intake of vitamin C has any clinical benefit is lacking, other than of course preventing scurvy.
Sorry!