Kidney function explained: How it works and what can affect it

Your kidneys are probably not the organ that is top-of-mind on most days, but whether you think of them or not, they are always working hard in the background to keep your body healthy.

Just as they work hard for you, you must focus on healthy lifestyle habits that can support your kidney health (and minimise risks of kidney disease).

But what does it take to maintain healthy kidneys? And, is it possible to improve kidney function naturally? We have all your answers in one easy-to-read package.

Remember, all of this is general advice designed to help you understand your body better. For any serious health concerns, we recommend contacting your regular healthcare team.

What is the main function of the kidneys? 

The main function of your kidneys is to filter toxins out of your body [1][2]. They do this by filtering waste out of your blood and turning it into urine, which is removed from your body each time you use the loo.

While that is their main purpose, it’s not their only task. Other important functions of your kidneys include:

• Managing blood pressure
• Producing vitamin D, which is key to bone health and making red blood cells
• Producing hormones that help to balance your sodium and potassium levels

How is kidney function tested?

Checking your kidney function is actually pretty easy. Most of the time, your doctor will use blood and urine tests [1][3].

From these test results, your doctor can estimate your glomerular filtration rate (GFR) [9]. This is the fancy name for a measurement of how much waste your kidneys can filter in 1-minute.

A high score would suggest normal kidney function, while a low score can suggest kidney disease. GFR rates can fluctuate, so it’s likely you’ll need to do more than one test to check for repeated patterns over time.

Other tests your doctor might recommend include [3][9]:

• Blood pressure tests
• Imaging tests like a kidney scan or ultrasound
• Kidney biopsy

If you are in a high-risk group for kidney problems, they might also suggest regular screening, such as once per year.

Can kidney function improve?

The human body has an amazing ability to heal and recover when we give it the right support. For example, there are many lifestyle habits that can help improve kidney function, such as eating well, getting regular exercise and quality sleep [4].

On the flip side, there are a number of underlying health conditions that can put strain on the kidneys, which can affect how they function. For example, high blood pressure, diabetes or high cholesterol levels [6]. Getting treatment for these issues can help keep your kidneys healthy.

Finally, there are some factors outside of your control – such as your age or a family history of kidney disease [4]. Which is why it’s so important to work with a qualified health professional, like your GP, on diagnosing and treating any health condition.

What influences kidney health over time?

Earlier, we mentioned some of the key factors that help keep your kidneys healthy – like diet, exercise and treating health conditions. Now, it’s time for us to dig deeper.

Hydration and nutrition

Keeping hydrated and eating well are 2 of the most important steps you can take to care for your kidneys. Let’s start with hydration.

Your kidneys need plenty of water to help them remove waste products by making urine. Dehydration can lead to dark, concentrated urine, which also means not all the waste has been filtered out [4]. It can also increase the risk of issues like kidney stones, which can lead to further kidney damage.

At a minimum, you should be drinking 1.5 litres of fluid each day. Water is the gold standard for hydration, but other drinks like tea and fruit juice also count toward your fluid intake [5]. 

Next, let’s talk about diet. According to the NHS, a healthy and balanced diet includes [7]:

•  At least 5 serves of fresh fruit and vegetables each day
• Some dairy or dairy alternatives
• Some starchy foods like potatoes and whole grains
• Some protein such as beans, fish, eggs and meat
• Low levels of saturated fat, salt and sugar 

When it comes to avoiding fat, salt and sugar, a good place to start is limiting ultra-processed foods. These are things like sausages, soft drinks and packaged breads [4].

In fact, one American study found that ultra-processed foods could increase the risk of kidney disease by more than 20%.

Another food to watch out for is salt. Keeping your salt intake to 6 grams (or 1 teaspoon) per day is best. We don’t just mean the salt you add to meals, either.

Many foods are high in salt without us realising – such as processed meats like sausages and bacon, cheese, smoked fish, packet crisps, pre-made sauces and stock [5].

If you need extra support with your diet, then we highly recommend working with your doctor or a registered dietitian.

Physical activity and weight

Alongside a healthy diet, it’s important to keep active and maintain a healthy weight. Research shows that physical activity lowers risks of kidney disease. That could mean heading to the gym or even getting your heart pumping by taking the stairs instead of the lift [4][5].

When it comes to physical activity, the NHS recommends [8]:

• At least 150 minutes (2.5 hours) of moderate exercise each week, such as a fast walk or cycling
• Strength training on 2 or more days per week, with a focus on all the major muscle groups 

As for weight management, we know that people living with obesity are at higher risk of kidney disease, especially those carrying weight around their mid-section.

We also know that losing weight can be easier said than done. Even when you have the motivation, there can be factors outside your control, such as genetics or metabolism.

We hope you know there are lots of support options available – whether that’s talking to your GP about a weight loss plan or joining a supportive community, like Juniper. 

With the Juniper Programme, you can access weight loss medication tailored to your health and goals — never one-size-fits-all. Our app helps you track progress, connect with your care team, adjust medication as needed, and access expert support. You'll also get structured tools to build lasting habits and ongoing care. 

Kickstart your weight loss journey with Wegovy, a groundbreaking weight loss injection that mimics the GLP-1 hormone to help control cravings, delay stomach emptying, and keep you feeling fuller for longer.

We help you make lifestyle and habit changes, and we’re in it with you for the long run, having helped thousands of women achieve their weight loss goals.

Sleep

According to new research, too much or too little sleep could affect your kidney health. Too much would be more than 10 hours per night, while too little is less than 6 hours per night [4].

A good rule of thumb is aiming for 7-9 hours of quality sleep each night, which is what works for most people.

Blood pressure and blood sugar control 

It’s important for your overall health to keep an eye on your blood pressure and blood sugar levels, but it’s especially important for your kidneys [2].

Both high blood pressure and high blood sugar can damage your kidneys. If this continues unchecked for a long time, it could lead to advanced kidney disease or kidney failure.

In good news, there are lots of treatment options that can help manage your blood pressure and sugar levels, so long-term damage is preventable [3].

Medications, smoking, and alcohol use

Remember how we said that your kidneys' most important job was to remove toxins and waste? Well, these lifestyle 3 habits can make it harder for them to do that job.

Let’s start with medications. Even common ones, like over-the-counter painkillers, can affect your kidney health [4][8]. It’s mostly a problem if you are taking too many or having them too often. So, be sure to follow the directions on the pack and speak to your doctor if you need further support for prescription medications.

Next, we have smoking. We know it’s not an easy habit to quit, but it’s an important change for your health. Some of the ways smoking can harm your kidneys include [3][4][5][7]:

• Cigarettes contain toxins that your kidneys have to work extra hard to remove
• Smoking is known to restrict blood vessels, which leads to high blood pressure
• It can lead to oxidative stress in your body

Finally, we have your alcohol intake. While many of us enjoy a drink here or there, having more than the recommended alcohol units each week can harm our kidneys [4].

Alcohol is dehydrating, which means it can make your kidneys work harder to filter out waste. It can also raise your blood pressure, which can lead to kidney damage if left unchecked. 

The key is drinking alcohol in moderation. That means 14 units or less per week, which is an average of 1 glass of wine or 1 pint of low-strength beer each day. It’s ideal if you can have a few alcohol-free days each week as well.

Can kidney failure be prevented?

The simple answer here is: yes, kidney failure can be prevented in most cases. Now that you can breathe a little easier, we wanted to go into more detail on kidney disease and how it progresses.

You might be surprised to learn that more than 10% of the UK population has some form of chronic kidney disease (CKD) [4]. But, how do you get kidney disease in the first place?

That comes down to many of the factors we mentioned earlier – like high blood pressure, smoking, drinking too much alcohol or a diet high in ultra-processed foods. Each of these has the potential to damage your kidneys.

When your kidneys are damaged, they stop being able to do their job of filtering waste properly. If that damage is short-term, it’s known as an acute kidney injury [4].

If that damage continues for the long-term, it can develop into chronic kidney disease. And if the damage continues long enough, then you might progress to kidney failure.

It’s time for a reality check: many people can keep chronic kidney disease under control, which means they can avoid it getting worse or progressing to kidney failure.

In fact, only 2 out of every 100 people with chronic kidney disease are likely to progress to kidney failure [6]. That doesn’t mean you can get complacent. But it also means you shouldn’t be too worried. Working with your doctor on a management plan is a great place to start.

Early intervention is also really important. That’s because a lot of kidney damage cannot be repaired, but further damage can be stopped with better health and lifestyle habits [7].

So, to sum it all up in a nice, neat package – kidney failure is not an inevitable outcome for people with kidney disease. There are also various treatments and lifestyle tips your doctor can provide to help you manage chronic kidney disease [6].

When should you seek medical guidance about kidney health?

When it comes to your health, it’s never a bad idea to talk to your doctor about doing a few checks. The more you know, the better you can support your body and its essential functions.

Early diagnosis of kidney problems is also super important because for many people, there are no symptoms until their disease has progressed quite a bit [1].

So, with that in mind, everyone is a good candidate for a simple kidney function test.

Some people who have higher risk factors might be recommended for regular screening. Examples of risk factors include [3]:

• A family history of kidney problems
• High blood pressure
• A history of smoking
• An acute kidney injury in the past
• Carrying weight around your belly

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