Vitamin C, or ascorbic acid is a water-soluble vitamin that plays a vital role in many metabolic processes including the immune responses. Within the immune system, particular cells called lymphocytes (white blood cells), require vitamin C for proper functioning. Vitamin C also helps protect cells from oxidative stress when your body is fighting an infection. The body produces specialised cells that help clean up cellular mess following infection, and these cells secrete vitamin C to help mop up free radicals.
Humans lack a key enzyme required to produce vitamin C from other compounds, so dietary intake of this vitamin through food is essential. This vitamin also needs to be a regular part of our diet because the body cannot store it for very long. Given its high-water solubility, it is easy to excrete from the body.
Vitamin C is plentiful in many fruits and vegetables that extend beyond the well-renowned orange. Good sources include lemons, limes, berries, kiwifruit, and vegetables such as broccoli, brussel sprouts, tomatoes and capsicum. Interestingly vegetables often provide more of this vitamin to the diet than fruits. In Australia, some 40% of vitamin C intake comes from vegetables and 19% from fruits. Vitamin C is a labile compound, this means it can be easily altered and can be affected by transport, shelf life, storage time and cooking practices. To get the most nutrients, it’s best to eat food as soon as possible after purchasing.
Research has shown vitamin C can help the immune system fight off bacteria and viruses. A recent review found that immune cells require vitamin C to produce proteins that activate the immune system throughout the body against virus attacks. It has been reported in at least 30 studies that regularly taking at least 200 mg of vitamin C daily, can reduce the severity and duration of the symptoms of the common cold. This was further pronounced in people who lived a very active lifestyle, whereby the severity and duration was halved. Some studies have also found some benefit from vitamin C supplements for preventing colds among those with pneumonia.
Deficiency of vitamin C can impair immune function. Given our abundant access to fresh fruit and vegetables, deficiency in Australia is uncommon. However there are a number of instances such as times of stress, poor diet, some medications and alcohol consumption that can increase our vitamin C requirements. Improving intake of fresh fruits, and particularly vegetables is an easy way to boost your vitamin C levels. Supplementation of vitamin C may be appropriate if your dietary intake is adequate.
- Carrillo AE, Murphy RJ and Chung SS. Vitamin C supplementation and salivary immune function following exercise-heat stress. 2008;3(4):516-30.
- Carr AC and Maggini S. Vitamin C and Immune Function. Nutrients. 2017;9(11):E1211
- De Tullio, MC. The mystery of vitamin C. Nature Education. 2010;3(9):48.
- National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. 2015.
- Hemila H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Syst Rev. 2013;(1):CD00980.
- Hemila H. Vitamin C and infections. Nutrients. 2017;9(4): pii E339.