Kiwi And Kidney Function Support

Overview

Kiwi fruit, also known as the Chinese gooseberry, is an edible berry of woody vines native to China and Taiwan.¹ Beneath the brownish-green furry skin hides the bright green flesh that is packed with vitamins and minerals. Owing to its high levels of vitamin C, E, and K, and high potassium content, kiwis are beneficial for kidney health. Potassium helps regulate chemical reactions and fluid balance in the body, which is vital for proper kidney function and can reduce the risk of contracting kidney stones. Good kidney function is important for proper waste removal from the blood and for controlling the levels of many substances in the blood. It also helps to control blood pressure. Read on to find out how adding kiwis to your diet can help to keep your kidneys healthy. 

Role of kidneys in the body

Kidneys are the filter system in our body. They remove waste products and excess fluid from the blood and as a result, produce urine. This process helps to maintain a stable balance of chemicals in the body. They are also important in the production of hormones that affect the function of other organs, for example, blood pressure regulation, calcium metabolism, and the production of red blood cells. It is important to maintain optimal kidney function in order to maintain the correct levels of water and other substances in the body. When this is unbalanced, it can make you feel unwell due to a build-up of toxins in the blood.² Kidney malfunction usually goes unnoticed for a long time and is often too severe and even irreversible by the time people start to feel symptoms.³ 

Common issues affecting kidney health

Some common issues that can affect kidney disease are high blood pressure, diabetes, anaemia, and malnutrition.⁴ Eating kiwi can help to mitigate some of these, as their high potassium content can help to lower blood pressure and the risk of kidney stones. Potassium has also been shown to lower the risk of diabetes (as lower potassium levels mean less insulin is released, meaning blood sugar spikes, increasing the risk of developing type 2 diabetes),⁵ which can contribute to poor kidney health. 

Nutritional composition of kiwi

Kiwi fruit is low in calories and high in fibre, as well as a range of other vitamins and minerals that support overall health and well-being, for example, antioxidants which protect against disease, vitamins that support immunity, and enzymes that aid digestion and manage blood pressure.⁶ 

Rich in Vitamin C

Vitamin C, also known as ascorbic acid, has many important roles within the body, including fighting infection, wound healing, and as an antioxidant to help neutralise harmful substances that are produced when we digest food. There is some evidence that suggests vitamin C can reduce the risk of getting kidney cancer. In a meta-analysis of the association between vitamin C intake and renal cell carcinoma (RCC) risk, it was found that consuming vitamin C reduces RCC risk.⁷

Rich in Vitamin E

Kiwis contain relatively high amounts of vitamin E compared to most fruits, which tend to be poor sources of this vitamin.⁸ Vitamin E is also recognised as an antioxidant, as well as having anti-inflammatory and immune-enhancing properties. Due to these, it has been found to be effective in the prevention and treatment of certain diseases. Studies in humans have shown that vitamin E may play a role in preventing and mitigating kidney disease.⁹ Other studies found that increased vitamin E intake from food improved kidney function,¹⁰ proving that kiwi is a good dietary choice for supporting kidney function. 

Rich in Vitamin K

Kiwi is one of the best foods for vitamin K, aside from dark green leafy vegetables. One serving of kiwi contains approximately 60% of the daily recommended vitamin K, making it an easy way to boost your levels of this vitamin in your diet.⁸ Vitamin K is involved in blood clotting. In terms of kidney health, vitamin K deficiency is thought to be a factor in kidney disease.¹¹ This may be due to the fact that vitamin K helps to prevent calcification, which is often associated with an increased risk of kidney stones.¹²

Potassium content

One kiwi provides you with 215 milligrams of potassium, which is about 6% of the recommended daily amount for adults.^13,14 Although this does not sound like a lot, it is a relatively high amount for the size of the fruit. Potassium is essential for normal kidney functioning. The kidneys rely on a fine balance between sodium and potassium; potassium increases the removal of sodium, which in turn lowers blood pressure, which is important in mitigating kidney damage.

In addition, higher sodium in the blood causes the kidneys to excrete more protein, which reduces the kidney’s filtration rate, ultimately causing deteriorated kidney function. A higher potassium intake also helps to prevent tubular damage. Tubular damage refers to damage to the tubule cells in the kidneys, the cells that reabsorb fluid and minerals from the blood when urine is produced. Tubular damage can lead to kidney failure, thus potassium is important in preventing this.¹⁵ 

Antioxidants in kiwi

As well as vitamin C, kiwi fruits are high in other antioxidants such as the carotenoids lutein, zeaxanthin, and ꞵ-carotene, which are thought to lower the risk of certain diseases such as cancers and eye disease.¹⁶ The antioxidant powers of kiwis can help reduce the risk of kidney injury. Antioxidants prevent the oxidation of food when it is broken down in our bodies. Oxidation is a chemical reaction that leads to the production of compounds called free radicals. Free radicals are highly reactive molecules that damage our cells, and a buildup of them causes oxidative stress in the body.

Oxidative stress can damage the kidneys by causing immune cells to release signalling molecules called inflammatory cytokines, which cause inflammation. Cytokines can promote damage to the kidney tissue by inducing apoptosis (planned cell death), necrosis (premature, unplanned cell death), and fibrosis (thickening and scarring of tissue). These processes all contribute to the development and progression of chronic kidney disease (CKD).³ Therefore, consuming kiwis and their wealth of antioxidants can help to reduce this risk. 

Benefits of kiwi for kidney function

Reduction of oxidative stress

The antioxidants found in kiwi help to prevent oxidative stress. Oxidative stress in the kidneys can cause both of the main types of kidney disease; acute kidney injury (AKI) and chronic kidney disease (CKD). AKI is characterised by a sudden decrease in kidney function, usually within one week, which can cause a buildup of toxins in the blood and reduced urine output, or both. CKD develops more slowly and is characterised by a gradual decline in kidney function. Both of these types of kidney disease have further health consequences. CKD tends to lead to cardiovascular disease, and AKI increases the risk of developing CKD and eventually end-stage renal disease, which is only cured by transplantation.³ Antioxidants are therefore vital in preventing the onset of these diseases. 

Regulation of blood pressure

Kiwi contains substances that help to lower blood pressure, namely potassium and the antioxidant lutein. Lutein helps to reduce the risk of artery thickening and atrial fibrillation, two processes that contribute to hypotension. In a study that observed the effect of apples versus kiwis on blood pressure found that eating kiwis decreased systolic and diastolic blood pressure. It was found that compared to apples, kiwis caused a higher increase in the concentrations of lutein and potassium in the blood, suggesting that these are responsible for regulating blood pressure.¹⁷

Kiwi and kidney health

The range of vitamins and minerals that kiwi contain makes them an ideal choice to boost your kidney health. There is lot of evidence to support the benefits of consuming kiwi on blood pressure regulation. In a study of men and women with elevated blood pressure, eating three kiwis per day lowered both systolic and diastolic blood pressures, compared with eating one apple a day. This is thought to be due to the high potassium and lutein content of kiwi fruit. It has also been shown that kiwi helps to protect cardiovascular health, which also helps to maintain a healthy blood pressure.¹⁷

New research has shown that vitamin C can help to prevent kidney injury in COVID-19 patients. A main feature of COVID-19 is the so-called ‘cytokine storm’, where inflammatory cytokines are excessively and uncontrollably released. As previously mentioned, these molecules cause inflammation, which is damaging to all organs, including the kidneys, where it causes tubular damage and kidney injury, impacting the filtration rate and therefore causing a buildup of toxins in the blood. If this is not treated, kidney failure ensues. Vitamin C not only has antiviral effects but also anti-inflammatory effects which help to fight the inflammation caused by the cytokine storm. The antioxidant properties of vitamin C can also help to counteract oxidative stress triggered by COVID-19.¹⁸

Incorporating kiwi into the diet

Kiwis are a versatile fruit which can be enjoyed raw, as they are, or in a range of drinks such as smoothies and juices. More creative ways to enjoy kiwis include ice lollies, muffins, salads, and salsas. According to the NHS, to count as one of your 5-a-day, a portion is two or more kiwis.¹⁹

Kiwi is also used by chefs as a meat tenderiser. This is due to an enzyme found in kiwi called actinidin which breaks down the protein and connective tissue of meat. This is either done using the underside of the skin after scooping out the flesh, or by pureeing the flesh and using it in a marinade.²⁰

Interactions with medications

Kiwi has been shown to slow blood clotting due to its high levels of vitamin E, which has natural anticoagulant properties, and counteracts the blood clotting effects of vitamin K.²¹ Consuming kiwi alongside medications that also slow blood clotting (anticoagulants such as clopidogrel, heparin, and warfarin) could increase the risk of excessive bleeding and bruising. This can be dangerous as it can increase the risk of brain haemorrhage, or losing too much blood from an injury. It is best to avoid eating kiwi if you have a bleeding disorder. It is also advisable to refrain from eating kiwi for a couple of weeks before a surgical procedure, to prevent the risk of bleeding too much during the surgery. 

Additionally, due to kiwi’s ability to lower blood pressure in some people, eating kiwi alongside taking antihypertensive drugs could potentially cause your blood pressure to drop too low. Limit your kiwi intake if you take blood pressure-lowering medications.¹⁷

Other lifestyle factors for kidney health

Hydration 

It is important to drink sufficient water every day to look after kidney health. Not only does this help to prevent urinary tract infections by flushing out infection-causing bacteria (and helping to dissolve antibiotics when you have an infection, to make them more effective), but it also helps to produce more dilute urine, meaning you don’t lose as many essential minerals from the blood. Drinking plenty of water also helps to prevent kidney stones, as it makes it harder for the crystals that create the stones to stick together.²²

A balanced diet and low-sodium intake

As always, the best way to look after your kidneys, and your health as a whole, is to ensure you are eating a varied and balanced diet with a range of vitamins and minerals. It is important to watch your sodium intake, as too much sodium can cause high blood pressure, which can be damaging to your kidneys. The main source of sodium in our diets is salt, which is usually found in high concentrations in ultra-processed and pre-prepared foods. Be mindful of this when thinking about your kidney health, especially if you already have kidney problems, or are prone to high blood pressure. 

Regular exercise for overall health

Exercise has benefits for the whole body, both physically and mentally, and this includes our kidneys. Exercise can help improve the filtration rate and function of the kidneys. It also helps to regulate blood pressure, meaning the kidneys are put under excess strain from high blood pressure. Exercise is especially important for people who already suffer from kidney disease, and can be beneficial alongside medical treatment such as dialysis or kidney transplantation. 

Summary

The kidneys play an essential role in the balance of fluids, electrolytes and other substances in our blood. They flush out toxins from the body, producing urine as a result. Kiwi fruit contains several beneficial vitamins and minerals that contribute towards healthy kidneys. These include vitamins C, E, and K, potassium, and various antioxidants.

These substances found in high concentrations in kiwis help to keep blood pressure low, reduce inflammation in the kidneys which can cause kidney injury, reduce the risk of kidney cancer, and help fight oxidative stress, a harmful process which damages the kidney tissue, decreasing their effectiveness. As with all aspects of health, leading a healthy and balanced lifestyle is key to looking after the health of your kidneys. This includes eating a balanced diet with plenty of fruit and vegetables to ensure you are getting enough vitamins and minerals, as well as remaining hydrated, watching your sodium intake and getting regular exercise. It is always best to speak to a healthcare professional for personalised advice if you are worried about your kidneys.