Healthy kidneys: how to protect them

The best way to protect your kidneys is to keep your blood pressure in check, go easy on salt, stay a healthy weight and keep moving. Your kidneys are two fist-sized filters sitting against your back. They clean your blood, balance your fluids and salts, and even make hormones. Most of us only think about them once something goes wrong. In this Healthcast episode a kidney specialist explains how they work, what quietly damages them, and what you can actually do about it. Got symptoms or worried about your kidneys? See your GP. This article is information, not medical advice.

What your kidneys actually do

You have two kidneys, each about the size of your fist. They receive a huge amount of blood from your heart because they juggle several important jobs at once:

• Filtering waste. Their main task: pulling toxic waste products out of your blood so you can pass them in your urine.
• Keeping fluids balanced. Not too much water in your body, and not too little.
• Managing salts and acidity. So your blood stays exactly as it should be.
• Making hormones. Including the one that tells your body to produce red blood cells.

The filtering happens in tiny units, roughly a million per kidney. Around 150 litres of pre-urine passes through them every day. Most of it is reabsorbed, so on average you are left with just 1.5 to 2 litres of urine. Because your kidneys do so many different things, kidney problems can show up in many different ways.

What damages your kidneys over the long term

The two biggest culprits are high blood pressure and diabetes. Together they cause more than half of serious kidney failure. The tricky part is that both can damage your kidneys for years without you noticing.

With high blood pressure, the small blood vessels in your kidneys are constantly under too much strain. Over time they narrow or get damaged, and scar tissue slowly forms in the filters. As the specialist puts it, you can easily have high blood pressure for 10 to 20 years and have no idea it is happening. With diabetes, years of high blood sugar damage those same small vessels, in your eyes, your nerves and your kidneys.

Other things that play a part:

• Too much salt. It raises your blood pressure and puts more load on your kidneys.
• Carrying extra weight. Your kidneys end up working overtime, like an engine running at too high a rev, which wears them out faster.
• Certain painkillers. More on that below.

Go easy on anti-inflammatory painkillers

One important point from the podcast: anti-inflammatory painkillers such as ibuprofen, diclofenac and naproxen (the NSAIDs) can harm your kidneys. They lower the pressure inside the filters and can cause inflammation in the kidney. Take them at high doses for a long time, say for chronic back pain or headaches, and you can end up with lasting kidney damage. You can buy them straight off the shelf, so people sometimes use too much for years without realising. Paracetamol is gentler on the kidneys in this respect. If you already have kidney damage or reach for painkillers often, talk it through with your GP.

How to keep your kidneys healthy

The good news is that most of it is in your own hands, with steps you probably already know from looking after your heart. The specialist highlights these:

• Get your blood pressure checked. Plenty of people do not know theirs is high. If it is, flag it with your GP.
• Eat less salt. A lower-salt diet can bring your blood pressure down noticeably, which is directly good for your kidneys.
• Move and exercise. There is evidence it helps prevent kidney damage, not just through your heart but with a direct effect on the kidneys too.
• Stay a healthy weight. So your kidneys are not running overtime.
• Prevent diabetes. Especially with extra weight, a family history, or gestational diabetes, get checked in good time.

And no, you do not need to drink four litres of water a day for this. According to the specialist, that adds nothing extra when it comes to keeping your kidney function healthy.

Does drinking lots of water really flush your kidneys?

This is a stubborn myth. Many people assume the more water they drink, the better they flush their kidneys through. The specialist is clear: that is not how it works. What matters is balance. Drink little and you pass less; drink a lot and you simply pass it back out again.

What does matter is avoiding dehydration. With heavy diarrhoea, vomiting or a fever you lose a lot of fluid, so you do need to drink more. Older people are especially at risk, because they feel less thirsty and dehydrate faster during something like a bug. Severe dehydration temporarily lowers your kidney function because too little blood reaches the kidneys. It usually recovers, but prolonged or serious dehydration can cause lasting damage. So drinking enough when you are ill is sensible; forcing litres down every day is not.

Is lots of protein or creatine bad for your kidneys?

This is the question the fitness world asks most, and the specialist gives a measured answer. First, an important distinction: protein and creatine are not the same thing.

Lots of protein. A diet with a very high protein intake can be a burden on the kidneys over the long term. The supply to the filters opens wide and your kidneys have to work harder to process all that protein (hyperfiltration), which over years can cause damage. But the specialist stresses this is about very high intakes. If you eat a normal diet and have healthy kidneys, there is nothing to change. And never start a low-protein diet on your own, because sometimes you actually need more protein. That is always tailored advice from a doctor or dietitian.

Creatine. Here there is often confusion. Creatine (the supplement) is not the same as creatinine (the waste product measured in your blood to estimate kidney function). Someone with a lot of muscle who uses creatine naturally has a higher creatinine reading, which can make their kidney function look worse on paper than it really is. The specialist describes bodybuilders being referred with “reduced kidney function” who, on a better test (such as cystatin C or a 24-hour urine collection), turn out to be perfectly fine. In other words, creatine mainly skews the measurement and is not a proven cause of kidney damage in healthy people. Unsure? Get it checked with a better measure.

What are the warning signs of kidney problems?

The frustrating thing about kidney problems is that they stay quiet for a long time. Your kidneys have a lot of spare capacity: you can live perfectly well on half your kidney function. Symptoms often only appear once the kidneys are truly on their last legs, and they tend to be vague and non-specific. Keep an eye out for:

• Tiredness you cannot really explain.
• Fluid retention, such as swollen legs or ankles.
• Feeling generally unwell for no obvious reason.

Because these signs go with all sorts of other things, a simple blood test through your GP is the way to check. If you have diabetes, high blood pressure or kidney disease in the family, get looked at in good time. If in doubt or if you have symptoms, always see your GP.