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Immune Boosting Powerhouses: Meet Vitamin C, D3, Zinc & Quercetin

True Protein Blogger 1 by Christine Bardajian | @eatinginmind reviewed by our Nutrition Team 12 April 2022

Let’s take a closer look at some of the key nutrients that support immune function. 

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Immune Boosting Powerhouses: Meet Vitamin C, D3, Zinc & Quercetin

Written by Christine Bardajian, Clinical Nutritionist. Adv Dip Clinical Nutrition, Adv. Dip Nutritional Therapeutics. 

Taking supplements that are backed by science could be a smart move to keep healthy and well. However, with so much on the market it’s often hard to know which ones are right for you.  

Our immune system relies on a complex interplay of many different factors. Let’s take a closer look at some of the key nutrients that support immune function.  


Quercetin is a plant flavanol from the flavanoid group of polyphenols. It is a plant pigment with potent antioxidants and is one of the most common and researched flavanoids. Quercetin displays a broad range of properties which can support your general health, and wellbeing.  

Quercetin has antioxidant properties making it ideal for supporting the body and immune system (3). These beautiful plant derived antioxidants bind to and neutralize free radicals, which can cause cellular damage within our bodies. Antioxidants are compounds in foods that scavenge and neutralise free radicals, reducing their harm to us. Polyphenols have been shown to also benefit the gut, where most of the immune system resides, a topic which has been subject to intense interest from the scientific community.  

Humans cannot make the plant derived flavanol Quercetin – but it can be found in many fruits and vegetables including grapes, berries, cherries, apples, broccoli, buckwheat and kale. Many of us don’t consume nearly enough fresh fruit and vegetables to get the amount of quercetin our bodies could use.  

Quercetin works best when it is paired with Vitamin C for optimal absorption and action, as it is not easily absorbed on its own. Studies suggest that quercetin supplementation may promote antioxidant production, and therefore support healthy ageing and reduce free radical damage to body cells, making this compound a powerhouse of benefits. 

Adequate Vitamin C is also vital as it is able to regenerate active quercetin in the body. Whenever an antioxidant performs its function in neutralizing a free radical, it is changed to an inactive form. In the case of quercetin, vitamin C can recycle it back into its active form. Therefore, vitamin C levels in the diet and supplementation must be adequate. 

Vitamin C 

Most of us have heard of this one. Probably the most well-known of the vitamins is Vitamin C, also known as Ascorbic Acid or Ascorbate.  

Vitamin C is an essential nutrient involved in the repair of tissue, the formation of collagen, and the enzymatic production of certain neurotransmitters. It is required for the functioning of several enzymes and is important for immune system function. It also functions as a powerful antioxidant.  

Vitamin C contributes to immune defence by supporting various cellular functions of both the innate and adaptive immune system. Innate immunity is general and non-specific, making it the body’s first line of defence against pathogens. Adaptive immunity is the type of immunity is built up as we are exposed to diseases and is also called acquired immunity. 

Vitamin C deficiency can result in impaired immunity and studies suggest that not only is Vitamin C useful in reducing severity of illness, it can prevent us from becoming sick with regular intake.  


Zinc is your immune systems best weapon. An essential mineral required for many important bodily functions, zinc activates enzymes, metabolic pathways and switches systems into gear. Without zinc, we just wouldn’t work very well, as Zinc deficiency can results in impaired immune responses. Despite this, many of us may be deficient in zinc and would benefit from zinc supplementation.  


Zinc is a powerful component of our innate immune system's fight against infection (8). When a virus infects a cell, it inserts a piece of its genetic code and an enzyme called replicase allows the virus to replicate. Zinc, as a player in our innate immunity, is able to block the replicase enzyme and, therefore, block the replication or spread of the virus.  

Vitamin D3 

Vitamin D is critical for white blood cell production of antimicrobial compounds. These compounds, found inside white blood cells, directly kill bacteria and fungi, helping  support the immune system.  

Most Vitamin D is produced via absorbing sunlight through the skin and we can also consume small amounts from food. Interestingly though, no two peopleabsorb vitamin D from thesun in the same way. In fact, there are a number of factors that influence how readily a personabsorbs vitamin D from the sun. 

Ever notice that people tend to get colds and flu in the winter when the sun is low? Research suggests that vitamin-D deficiency may be one of the primary reasons people get more colds and flu in the winter when sunshine is less available. 

Vitamin D supplementation may limit the instance of cold and flu as well as reduce upper respiratory infections by 70% in those who were deficient in the vitamin. People that weren’t as deficient still saw a reduction of 25%. In addition, the authors noted that the evidence was of “high quality.” Interestingly, these benefits were not seen if vitamin D was given in large infrequent doses as compared to daily or weekly dosing (7).  

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IMPORTANT INFORMATION: all content provided here is of a general nature only and is not a substitute for individualised professional medical advice, diagnosis or treatment and reliance should not be placed on it. For personalised medical or nutrition advice, please make an appointment with your doctor, dietitian or qualified health care professional.


Key vitamins and minerals for healthy immune function