For most of us, getting a cold results in nothing more serious than slowing us down, getting a runny nose and missing work or school.  However, for some with weakened immune systems it can lead to more critical conditions like pneumonia.  During winter most of us want to ensure we have an immune system that will help fight off colds.  

Vitamin C, (or ascorbic acid) has been a popular remedy for colds, with people recommending taking oranges or lemons to help alleviate the symptoms. Although vitamin C was known to help prevent scurvy, it became associated with the common cold after Linus Pauling, a Nobel Laureate in chemistry, wrote in 1970 that vitamin C prevents and alleviates episodes of the common cold.  However, his work was later challenged as it was shown it was not based on a representative sample of the general population. Nevertheless, Linus Pauling’s work opened up further research into the effects of vitamin C.(1)

How does vitamin C support the immune system?
Over the years there has been conflicting research about the effects of vitamin C on reducing the frequency, length and severity of the common cold. 

A study was carried out to determine the immune-enhancing role of vitamin C and zinc and it’s effect on clinical conditions.  It was observed that vitamin C concentrations rapidly decline in the plasma and leukocytes during periods of stress and infection. By supplementing with Vitamin C, components of the human immune system such as antimicrobial and natural killer cell activities, lymphocyte proliferation, chemotaxis, and delayed-type hypersensitivity are improved. It was seen that both Vitamin C and zinc reduce the risk, severity and duration of infectious diseases.(2)

Vitamin C has also been shown to be useful for colds when people have been exposed to brief periods of severe physical exercise, like marathon runners, skiers and soldiers on subarctic exercises.  Regular supplementation of vitamin C trials have shown that severity of colds is reduced and that duration of a cold can decrease by 8% for adults and 14% for children.  Although, this was not replicated in the few therapeutic trials, given the benefits of vitamin C seen in the regular supplementation studies, it may be worthwhile to take vitamin C. It was concluded in the study that common cold patients test on an individual basis whether therapeutic vitamin C is beneficial for them.(3)

Vitamin C supports the immune system and protects from some chronic diseases.  In the EPIC-Norfolk prospective study it was shown there is an inverse relationship between plasma ascorbic acid concentration and mortality from cardiovascular disease and ischaemic heart disease (men and women), and cancer (for men only).(4)

How much Vitamin C do we need?
The National Health Service in the UK recommends that adults need 40 mg of vitamin C a day, as it cannot be produced or stored in the body. Therefore, it needs to be included in our daily diet.  However, note that taking large amount of vitamin C (more than 1,000 mg a day) can cause stomach pain, diarrhoea and flatulence.(5)

The Recommended Dietary Allowance set by the Food and Nutrition Board, Institute of Medicine, National Academies is higher with an intake of 75mg/day for women and 90 mg/day for men to provide antioxidant protection.  And as smokers suffer increased oxidative stress and metabolic turnover of vitamin C, their recommended intake is increased by 35 mg/day.(6)

Some common foods and their typical vitamin C content are detailed below.

Vitamin C (total ascorbic acid)

As seen from the table above it is easy to obtain the recommended daily allowances of vitamin C through our diet. However, when taking Vitamin C, either through the diet or as a supplement, you need to be aware that your body may not absorb it all. It is difficult to measure how much vitamin C is absorbed, as this depends on certain features of the digestive system that are unique to each individual. There is some evidence that zinc and vitamin C taken together are more effective.  

There are differing views on the effects of vitamin C on the common cold but due to its relatively safety and easy availability, it is thought that there is no harm in taking vitamin C when we catch a cold.  However, we need to understand that there is often more than one reason for a compromised immune system that results in catching the common cold, this could include zinc deficiency, stress, lack of sleep, etc.  So, vitamin C on its own will not be the only solution to reducing the length and severity of the common cold.  Stay healthy this winter by eating balanced meals, which also contain fruits and vegetables that provide you with a variety of nutrients to support your immune system.

The information in this article is not intended for medical or nutritional advice. If you are under the care of a health care professional or currently using prescription medications, you should discuss any dietary changes or potential dietary supplements use with your doctor, and should not discontinue any prescription medications without first consulting your doctor.  

This article first appeared in Good Zing 


1) Vitamin C supplementation and the common cold–was Linus Pauling right or wrong.

2) Immune-enhancing role of vitamin C and zinc and effect on clinical conditions

3) Vitamin C for preventing and treating the common cold

4) Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study: a prospective population study. European Prospective Investigation into Cancer and Nutrition

5) NHS, vitamins and minerals

6) Food and Nutrition Board, Institute of Medicine, National Academies. Institute of Medicine (US) Panel on Dietary Antioxidants and Related Compounds