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Immunity

How well do you know vitamin C and its role in immune system health?

Dr Jane Winter
Written by Dr Jane Winter | Dietitian, Science Communication Manager
Sources of Vitamin C - citrus fruit sliced open

We all know vitamin C is important for immune health, which is why many of us reach for the orange slices when we feel a cold coming on. But, there’s far more to this micronutrient than just citrus fruits. So, what is the science behind vitamin C? What foods is it found in? How can it support the immune system? Here’s what you need to know.

What is vitamin C?

Vitamin C is an essential micronutrient that is important for a range of different processes within the body. You may also know it by the name ascorbic acid. Not only is vitamin C important for our immune health, it also assists with wound healing, the repair and maintenance of cartilage, bones and teeth and the absorption of iron.

Vitamin C is water-soluble (meaning, it dissolves in water), and is naturally present in many foods. Unlike many animals, humans can’t make vitamin C within the body, which means we have to consume it from our diet or through supplementation[1].

Vitamin C and the common cold

In 2013, a scientific review was published that examined the effect of vitamin C on relieving the symptoms of the common cold[2]. The authors found a consistent effect in reducing the duration of common cold symptoms. Regular vitamin C intake (with most studies using 1000mg per day) was associated with a 14.2% reduction in cold duration in children and 7.7% reduction in adults.

Vitamin C deficiency results in an impaired immune system. In turn, a weakened immune system can lower vitamin C levels due to inflammation in the body and pressure on the metabolism. So, it’s important to make sure you’re getting plenty of vitamin C to support health and wellbeing and your immune system response.

What other roles does vitamin C play in the body?

Vitamin C is necessary for the growth and repair of all tissues in our body. It’s involved in[3]:

  • The functioning of the immune system
  • Keeping the bones, teeth, connective tissue and bone cartilage strong and healthy
  • Acting as a powerful antioxidant
  • Improving the absorption of iron (the type found in plant-based foods, not meat products)
  • Producing collagen, a protein in the structure of the body essential for your muscles and skin
  • Kiwifruit
  • Strawberries
  • Kakadu Plums (Australian native plum)
  • Capsicum, particularly red (which are ripened green capsicums)
  • Blackcurrants
  • Oranges, mandarins, lemons and other citrus fruit

How does vitamin C help to support the immune system?

Vitamin C plays an important role in supporting both the innate (the defence mechanisms that immediately attack foreign cells in the body) and adaptive immune system (the second line of defence that prevents them from growing) in the body[4].

Firstly, it supports epithelial barrier function. This barrier regulates nutrient absorption and also prevents the invasion of pathogenic bacteria (the bacteria that can cause disease) in the body. Vitamin C also promotes the oxidant scavenging activity of the skin, which protects against environmental oxidative stress[5].


How to add more vitamin C into your diet

Vitamin C cannot be stored in the body for long. So, eating an abundance of fresh fruits and vegetables is important to ensure your body can make the most of it.

The recommended dietary intake (RDI) for adults is 30mg per day. If you’re following the common advice of eating two servings of fruit and five servings of vegetables,[6] you’re on the right track to meeting your daily vitamin C target[7].

Most fruit and vegetables feature some vitamin C, but there are some stand -outs that have higher levels than others. Foods that are high in vitamin C include:

  • Kiwifruit
  • Strawberries
  • Kakadu Plums (Australian native plum)
  • Capsicum, particularly red (which are ripened green capsicums)
  • Blackcurrants
  • Oranges, mandarins, lemons and other citrus fruit
  • Papaya
  • Guava
  • Tomatoes
  • Broccoli
  • Brussel sprouts
  • Kale and Spinach.

When it comes to getting your daily dose of vitamin C, how you cook your food plays a role too. To retain as much of the vitamin C content as possible, cooking methods that require shorter periods of time are your best bet— such as stir-frying or steaming briefly. Even frozen vegetables can be a convenient way of supporting your daily vitamin C intake. There are so many delicious, vitamin C and nutrient-rich recipes ready for you to explore online via our hub. All recipes are written, tried, tested and loved by our in-house Nutritionists and Dietitians.

References:

[1] https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/

[2] Hemilä H, Chalker E. Cochrane Database of Systematic Reviews 2013, Issue 1.

[3] https://www.healthdirect.gov.au/vitamin-c

[4] Carr AC, Maggini S. Nutrients 2017

[5] Carr AC, Maggini S. Nutrients 2017

[6] https://www.eatforhealth.gov.au/food-essentials/five-food-groups/fruit

[7] https://www.nrv.gov.au/nutrients/vitamin-c