Rich in vitamin C, the kiwi fruit is one of the most immune-boosting fruits nature has to provide. Kiwis are surprisingly a type of berry – one of the Chinese gooseberries specifically. From the exterior they appear as fuzzy, brown, and small-looking fruit but within, a powerhouse of nutrient-dense soft fruit.

Kiwis contain an abundance of vitamins and plant protection compounds which, when consumed, offer an array of health benefits to your body. At first, it may seem like a humble fruit but be prepared to find out the extent to which it can support your immune system.

Introduction

Kiwi

Kiwi – also known by its full form as Actinidia deliciosa is part of the Actinidiaceae family. They are native to China and Taiwan being grown in areas around the world such as New Zealand and California. Due to the variety of bioactive compounds such as vitamins and minerals found in kiwis, extensive research has been done investigating the benefits of these and linking consumption to improvements in immune, digestive, and metabolic health.

Importance of a healthy immune system

Your immune system plays a vital role in your overall health, a well-functioning immune system is essentially critical in survival. This means it must be continually active, able to detect signs and dangers quickly, and overall maintain high alertness levels through continuous surveillance.¹

Although you may subconsciously regard any organ as a more substantial thing than the immune system, immunity actually contributes and regulates the functioning of the rest of the body so in this sense, it’s pretty important.

Nutritional values

A 100g portion of raw kiwi approximately contains:

• 58 kcal
• 1.06 g protein
• 3g fiber
• 16 mg magnesium
• 198 mg potassium
• 74.7 mg vitamin C
• 26 µg folate
• 40.3 µg vitamin K
• 1.3 mg vitamin E

Vitamin C is an important contributor to normal immune function. It is recommended by a trusted source that adults aged between 19 and 64 require 40mg of vitamins a day, this means one kiwi, roughly 90g provides 67.23 mg which is more than sufficient.

Since they are a highly concentrated source of vitamin C, it would not be recommended to focus on other sources. If you wish to do so, considering a variation in your diet including kiwis some days would be sensible. It is key to remember however that large enough amounts to cause any side effects would be exceeding 1,000 mg per day which is very difficult to do!

• As evident, kiwis are incredibly rich in vitamin C particularly, and surprisingly, they contain more vitamin C than oranges at 53.2 mg for 100g!
• Amongst the other vitamin C rich fruits, papaya contains 60.9 mg of the vitamin, strawberries contain 58.8 mg and lemons contain 53 mg. So we can really see where kiwis stand – they really are dark horses!

Other essential nutrients

Vitamin K, vitamin E, folate and dietary fibre are all also essential in the contribution of a healthy immune system.

Vitamin K

• Vitamin K is a fat-dissolvable vitamin with two further variants – vitamin K2 and K1²
• It plays a role in immune and inflammatory responses particularly those regulated by T cells, and it does this by acting as a cofactor for plasma proteins³
• Kiwi has high amounts of vitamin K contributing to the normal functioning of the immune system

Vitamin E

• Powerful dietary antioxidant affecting immune function
• Shown to improve the immune response through T cell function similar to vitamin K⁴

Folate

• Essential in cell growth and proliferation through the stabilizing of your DNA
• Particularly high quantities required during pregnancy⁵

Antioxidant properties of kiwis

Role of antioxidants in your immune system

Antioxidants are substances which protect many cells from the damage caused by unstable molecules called free radicals.

The human body requires adequate amounts of bioactive compounds known as antioxidants. When any of your tissues undergo oxidant-mediated injury, cells of your immune system will produce a reactive free oxygen species as part of the body’s defense.⁶

• If these species, known as free radicals, accumulate and are left free to roam the body, they will find other components to react with, hence the risk of damage to your body
• Dietary antioxidants can be obtained for instance, from kiwis
• These antioxidants are required to stop the immune cells damaging themselves

Specific antioxidants in kiwi

Kiwis contain the antioxidants quercetin, lutein, and zeaxanthin.

• Quercetin is known for its anti-inflammatory, antiobesity, antihypertensive, and anti hypercholesterolemic properties, and more.⁷ That’s a whole lot of diseases being targeted
• It is widely used in metabolic and inflammatory disorder treatment
• The reason why all of these can be targeted is because they all share the presence of free radicals as one of the key contributors to the development of each disease
• Quercetin also has the potential to protect against external, environmental causes of free radicals; for instance, smoking⁸
• The tar from cigarettes is one of the sources of free radicals
• This tar damages erythrocyte membranes (red blood cells)
• Quercetin have been found to protect erythrocytes from this membrane damage

Lutein and zeaxanthin come from the same family of carotenoids, being very similar in structure. The recommended daily intake for adults is around 10 mg and 2 mg respectively.⁹

• Synthesis of these compounds in humans generally isn’t efficient so eating a lot of dark, leafy vegetables and fruits such as kiwi contributes to the proper functioning of certain organs within the body
• The effects displayed by carotenoids are due to their protection against oxidative stress and scavenging abilities for free radicals

Anti-inflammatory effects

Relationship between inflammation and immune function

When your immune system responds to anything harmful and detects danger, things such as pathogens, toxic chemicals, damaged cells etc, then it produces an inflammatory response.¹⁰

• Inflammation is a defense mechanism vital for health and survival at times
• There can be acute inflammation at sites of injury which causes rapid recovery however there can also be uncontrolled inflammation where which leads to chronic inflammatory diseases
• Simple signs of inflammation are redness, pain, heat and swelling, in more serious cases a loss of tissue function
• During this time, many events happen without you even knowing. This includes an accumulation of white blood cells, vascular permeability changes, dilation and constriction of veins and arteries, etc
• Inflammation occurs via different pathways, if you have a well-functioning immune system, any of these pathways can be used and appropriate bodily responses can be achieved rapidly, so you don’t feel so bad

Kiwi’s anti-inflammatory compounds

Kiwi contains both phytochemicals and enzymes which impact inflammatory processes and immune function.

In a study, phenolic acids were shown to be the most abundant antioxidant phytochemicals in the kiwi berry and significant quantities of protocatechuic acid.¹¹

• A study showed phenolic acids as having powerful antioxidant properties and anti-inflammatory effects
• Protocatechuic acid also has many biological functions such as producing antihyperglycemic, antibacterial, antioxidant, and anti-inflammatory effects

Impact on gut health 

What has gut health got to do with the immune system?

The gastrointestinal tract provides a whole array of complex bacteria and microorganisms. The gut bacteria also known as the microbiota, has adapted over time to provide us with many benefits. To name just a few, these include:¹²

• Production of nutrients
• Detoxification
• Digestion
• Regulation of the immune system, etc

With the collaboration between the gut microbiota and the host immune system, some autoimmune diseases have been discovered to link with gut bacteria. Therefore, maintaining a healthy gut ensures the reduced likelihood of gut-associated immune disease.

Kiwi and a healthy gut 

In a clinical trial, the kiwi berry was found to increase bowel frequency and reduce gastrointestinal symptom aggression significantly. Particularly consuming the skin of kiwifruit may have beneficial effects on gut health that could not be fully gained from eating the flesh inside alone.¹³ Kiwi skin is perfectly edible once thoroughly washed. Kiwi has also been shown to produce prebiotic effects that is the increase in the content of faecal lactobacilli and bifidobacterial.¹⁴

Incorporating kiwi into a balanced diet

Kiwis are mostly enjoyed raw and unprocessed which is perfect as it adds to the preservation of the nutrients you will receive from consuming the fruit.

Creative ways to include kiwi in meals

1. Smoothies – an easy, healthy, and quick breakfast or drink any time of the day, particularly in warmer weather. A kiwi, mango, and pineapple smoothie - This is a great recipe you can check out!
2. Fruit salad – a visibly pleasing, healthy, and hydrating snack that is quick and easy
3. Vegan tacos – A filling meal full of whole foods and tasty flavours including kiwi

Potential considerations and precautions

As with any fruit or food in general, it is possible to have or acquire sensitivity so you must monitor your health when introducing a new component in your diet. Kiwi allergy is a thing, so if you have any of the following symptoms, you should seek medical guidance:

• Itchy/ tingly mouth
• Stomach pains
• Rash
• Trouble breathing

Some flavonoids may interact with some medications although this is not common, and kiwi generally has no interactions with most medications. If you are concerned you should consult with a medical professional.

Summary

There has been a significant amount of research on the effect of kiwi and specifically the antioxidants, phytochemicals, and other properties on the support of the immune system. It is recommended that you include various fruits as part of your five-a-day or as a balanced diet to ensure your immune system gets the fuel it needs to function well.

Key points

• Maintaining a balanced diet is the best thing you can do to strengthen your immune system
• Kiwis are exceptionally rich in vitamin C and antioxidants which are the main reasons for consumption of them supporting your immune system
• If you suspect any sensitivity or allergy consult medical guidance
• Gut health and immune health have been shown to be interlinked and so consuming fruits with gut- beneficial nutrients could strengthen your immune system
• Kiwi’s can also have amazing anti-inflammatory effects for your immune system, reducing the likelihood of future inflammatory disease onset