It’s cold and flu season, with susceptibility often blamed on a poor immune system. Andrea du Plessis, Vital Health Foods’ nutrition expert, spoke to Omeshnie Naidoo


What is the immune system?

The immune system is the body’s natural protection against harmful bacteria, fungi, viruses and other organisms that could cause infections. It involves a complex system of immune cells that are distributed throughout the body. While immune cells generally circulate through the bloodstream, areas where harmful organisms are likely to enter the body such as the respiratory tract and digestive systems contain higher concentrations of certain immune cells ready to fight invading organisms.

Where in the body is the immune system, is there an organ that is a good indicator of how your immune system is doing?

The immune system is complex.

Think of it as a system of immune cells, including white blood cells and many other immune cells, which are distributed throughout the body.

These immune cells are produced by a variety of glands and tissues in the body, including the lymph nodes, the thymus gland, bone marrow, the digestive system, the tonsils and adenoids.

Blood levels of the various immune cells, compared with their normal ranges, would be used to assess a person’s immune function.

How does one know if we have a strong immune system or not?

Susceptibility to infections, especially upper respiratory tract infections such as colds and flu, serve as strong indicators of a weak immune system. Gastro-intestinal infections are also common in individuals with weakened immune systems.

How does one build a strong immune system … what are the building blocks?

Good nutrition is the cornerstone of a healthy immune system. The immune system, consisting of the variety of immune cells, as well as the glands and tissues that produce these immune cells, rely on optimal intakes of a variety of nutrients, notably:

Vitamin C


Vitamin A

Vitamin D

Omega 3

Vitamin C is said to steal the show when one considers the immune-boosting benefits of nutrients. How does it work?

Since the immune system is responsible for protecting the body against invading viruses and bacteria, it comes as no surprise that vitamin C’s actions are directly focused on the immune cells.

According to test results published in Advances in Experimental Medicine and Biology, there is up to 100 times more vitamin C in our white blood cells than in the plasma (the fluid component) of our blood.

When the body is fighting a cold or flu virus, vitamin C supplementation has been shown to increase the numbers and activity of our immune cells, as well as protecting our immune cells against premature degeneration.

At the onset of an infection, increase in the usage of vitamin C by our immune cells result in a decrease in vitamin C levels. During this time, it seems the body is able to retain dietary vitamin C more effectively, because it is required to help fight the infection.

Taking 1000 mg vitamin C a day can reduce the risk for colds and flu. A review published in the Cochrane Central Register of Controlled Trials revealed that a daily dose of 1000 mg of vitamin C can reduce the severity of the symptoms of a cold.

Contrary to the popular belief that oranges have the highest levels of vitamin C, guavas, sweet red peppers, chillies, lemons, uncooked cauliflower and strawberries contain more vitamin C than oranges. Grapefruit and blueberries also contain vitamin C.

With many vegetables listed as concentrated vitamin C sources, it is important to consider the fact that heat exposure during cooking destroys up to 50% of the vitamin C. It is therefore important to find ways of ingesting vegetables such as red peppers in their raw state to get the desired immune- boosting benefit.

What other foods offer natural remedies to colds and flus or support to the immune system?

Garlic is a herb, most often used for its flavour in food, but also as a natural medicine, because it has many healing properties. Garlic’s greatest benefit in supporting the immune system is in its anti-microbial properties:

Antiviral: garlic has activity against a variety of influenza virus strains;

Antibacterial: garlic deactivates certain enzymes that are needed for bacteria to grow;

Antifungal: garlic reduces the growth, activity and survival of candida albicans;

Garlic’s antimicrobial effects are mostly ascribed to the sulfur containing compounds, such as allicin and ajoene. The antimicrobial effects of garlic oil is stronger than that from garlic powder, or dried garlic.

In addition to garlic’s antimicrobial effects, it also contains immune stimulatory effects, including:

Increased immune cell production

Increased immune cell activity

Improved immune system response to infection

Garlic supplements have even been shown to slow down the immune system decline that is associated with ageing.

What do we as individuals do, habits etc, that damage or hinder our immune system?

Certainly eating an inadequate or unhealthy diet – the immune system is dependent on a variety of nutrients for optimal functioning.

Lack of sleep: even losing one hour from your usual sleeping pattern can decrease the body’s defences the next day.

Stress: stress and the body’s hormonal response to pressure is known to break down the immune system’s defences.

Lack of exercise or excessive exercise: 30 minutes 3 to 5 times a week stimulates the immune system’s function. A lack of activity, as well as excessive high intensity exercise (which increases the body’s need for vitamin C), are known to impair the immune system’s function.

Chronic exposure to infectious diseases.


The use of certain medicines, such as antibiotics or immune-suppressive therapy often typically to transplant patients.


Certain diseases including HIV infection and cystic fibrosis.