What are kidney stones?
Kidney stones come in three common types. The most common is Calcium Oxalate, which causes 80% of all stones in the UK. In men, the next most common is Gout or Uric acid stones, which account for 20% of stones in the UK but 40% in countries with high red meat consumption. In women, the next most common is Infection stones (the classic "stag horn" stone), which often causes recurrent cystitis.
What causes kidney stones?
There are many causes of kidney stones, but they often form when urine becomes concentrated with minerals (calcium, oxalate, phosphate, urate or sodium) and lacks in potassium citrate. Some bacterial urine infections also raise the pH of urine, which precipitates the minerals. Kidney stones are primarily a disease found in developed countries rather than developing or poor countries, which is probably due to diets containing excessive calories, processed meat, salt, fructose (fruit sugar), beer and spirits.
Signs and symptoms
Kidney stones may sit quietly in the kidney doing nothing for years or only cause recurrent cystitis (especially in women); however, they often become evident when they pass from the kidney to the ureter. At this point they usually cause severe pain from the loin to the groin, blood in the urine and/or a persistent, painful need to urinate. These symptoms can also be accompanied by nausea and vomiting due to the severe pain. If a stone in the ureter is associated with pain and a fever it becomes a medical emergency.
10 ways to reduce your risk of kidney stones forming
- Drink at least 2.5 - 3 litres of fluid every 24 hours. Aim for at least 10 mugs a day or over 3.5 pints. It does not all have to be water - tea, coffee, milk and diluted low sugar juice or flavoured drinks are just as good. Avoiding dehydration is the single most important step to take to avoid kidney stones. Drink regularly out of habit and well before you feel thirsty. Start the day with a large drink. Take a litre bottle of something you like to drink with you to work and drink at least two of these bottles a day. Drink more if you work in a hot environment.
- Reduce intake of sugary drinks. Don't drink sugary drinks that may contain large amounts of fructose corn syrup like normal Cola, Pepsi, energy drinks, lemonade or milkshakes. Excessive dietary fructose has a strong association with calcium oxalate kidney stones. Diet or zero sugar fizzy drinks are fine.
- Drink milk and eat dairy food. People who do not drink milk or eat dairy food get stones more often. The calcium in milk also helps prevent bone thinning (osteoporosis) and hip fractures in later life. Skimmed milk, 1% or semi-skimmed and low fat products are just as high in calcium and as good at preventing stones, but contain less fat. Look at milk and dairy food labels for calcium content. Adults should aim for 700 - 1200mg of calcium a day.
- Drink alcohol in moderation, or not at all. Alcohol is as good as water at preventing calcium stones but beer and spirits increase the risk of gout kidney stones and so you should stop drinking these if you have gout stones; however, wine is probably fine to drink in moderation, even if you have gout. Gout is nine times more common in men than women and causes 20% of all kidney stones in men and less in women. Drink responsibly.
- Drink before bed. Stones probably grow most at night when you are not drinking and are relatively still, so drink fluid before bed if you can tolerate getting up once or twice during the night to urinate.
- For recurrent stone formers (more than one a year), if the above does not work, consider drinking an additional 500ml of natural orange juice (from concentrate or fresh, not squash) or 60ml of lemon juice diluted in a litre of water before bed. This will not dissolve calcium stones but these drinks contain a significant amount of potassium citrate, which gets into the urine and helps to prevent calcium oxalate and urate stones from forming in the first place. If you are diabetic then the lemon juice diluted in water contains a lot less fructose than the orange juice, depending on the brand.
- Follow NHS advice regarding a healthy diet. The NHS Eat Well Food Wheel is an excellent guide to the relative proportions of the different food groups we should eat every day. Especially pay attention to eating less than 6 grams of salt per day and less than 70 grams (cooked weight) of red or processed meat per day. Processed meat refers to meat that has been preserved by smoking, curing, salting or adding preservatives and includes sausages, bacon, ham, salami and pates. This will also help to avoid the increased risk of bowel cancer, which is associated with excess processed meat intake
- Maintain a healthy weight. Obesity (when Body Mass Index is greater than 30) doubles the risk of kidney stone recurrence if you are a woman and increases risk by 30% for men. Try to lose weight gradually by adopting a healthier diet, taking more regular brisk walking, following the NHS weight loss plan or consulting your GP.
- Reduce your intake of oxalate (probably not applicable to women under 35). Avoid eating spinach, swiss chard, rhubarb or beetroot more than twice a week. These foods are especially high in oxalate. Avoid excess vitamin C supplements (less than 1000mg per day), which are turned into oxalate. Diabetics also pass significantly more oxalate in their urine than non-diabetics and so it may help to reduce your levels of oxalate if your diabetes is kept under good control by eating healthily and proper regular monitoring.
- Eat five fruit and vegetables a day and reduce your intake of processed foods. Processed foods are often high in salt or added sugar and fat. Unprocessed foods are often richer in potassium and there is evidence that patients who eat up to five portions of these foods a day probably get less kidney stones in the long run. Potassium isn't only present in oranges and bananas, it is also found in dairy (milk or yoghurt), nuts and seeds (especially peanuts, sunflower seeds and hazelnuts), all types of beans, vegetables (especially carrots, cabbage and squash), tomatoes, starchy foods (including pasta, potatoes and wholemeal bread), fish and pork.
While fluid and diet is very important, at least 1% of kidney stones may have a significant underlying medical cause like hyperparathyroidism (especially in women) or an inherited cause like cysteinuria. Gout and recurrent infections are common associated problems that also need separate investigation and treatment to prevent recurrent stone growth.
Please note this advice only applies to kidney stones in adults and not children.
This advice is based on a variety of evidence including randomised trials (Pak and Borghi), prospective epidemiological studies (Curhan), laboratory work (Stickler), and US Department of Food and Agriculture food lists (website). A high potassium diet can be dangerous in patients with severe kidney impairment or on dialysis who are usually advised to be on a low potassium diet. This leaflet represents the personal advice of Mr Jonathan Ord who is a member of the British Association of Urological Surgeons and is not the official advice leaflet of the British Association of Urological Surgeons (see their website, or the NICE guideline 2019). However, most points are consistent with other advice leaflets produced.
Last updated Wednesday 27 November 2019
First published on Thursday 2 May 2019