Our kidneys play a number of vital functions helping to regulate fluid, produce hormones and remove waste products from our bodies. Kidney stones are small, hard stones made of mineral and acid salt crystals, which form inside the kidneys. The most common type (70-80%) are calcium oxalate stones and the main mechanism involves the calcium/oxalate balance in urine.1,2
Kidney stones are common and appear to be on the rise in recent years.1 According to The Kidney Foundation of Canada, about 12% of men and 6% of women will have a kidney stone during their lifetime.1 Having had one kidney stone increases the chance of having another.1
Risk factors for kidney stones include family history, certain medical conditions and medications, as well as a number of dietary factors, such as insufficient fluid and dietary calcium intakes.1,2 Symptoms can include severe pain, nausea, vomiting, fever and blood in the urine.1,2 Since kidney stones often cause severe pain and may lead to chronic kidney disease, prevention is key.
Diet and kidney stone research and recommendations
A 2020 meta-analysis examined the evidence on dietary factors for the primary prevention of kidney stones.6 This review identified a number of protective factors including fluid and water intake, a DASH-style diet (which emphasizes milk products, vegetables and fruit), dietary calcium and potassium, vegetables, fruit, dietary fibre, coffee, tea and alcohol. Whereas risk factors identified by this study included obesity, dietary sodium, fructose, meat, animal protein and soda. A 2021 meta-analysis that investigated the effect of diet and fluid intake on recurrent kidney stones confirmed that fluid intake significantly reduces the recurrence of kidney stones.7 This review also found that a normal calcium, low-sodium diet markedly reduces calcium stone recurrence. However, the findings from this study suggest that a low-protein diet, with or without fibre, does not affect the recurrence of calcium stones.
The Kidney Foundation of Canada and the U.S. National Kidney Foundation recommend a number of general dietary strategies to help reduce the risk of kidney stones.1-4 These include drinking plenty of fluids to avoid dehydration and make urine less concentrated.1,4 Low water intakes substantially increase kidney stone risk, so adequate fluid intakes are paramount.5 Consuming enough dietary calcium from foods such as milk, yogurt and cheese is also recommended.4 Research shows that higher dietary calcium intake from foods is associated with a lower risk of kidney stones.1,5 Other healthy eating habits such as avoiding too much salt and sugar are important as well.4
Adequate intakes of fluids and dietary calcium (from foods such as milk products) are among the evidence-based dietary strategies recommended to help reduce the risk of kidney stones.3-5 Kidney foundations encourage people to:1-4
- Drink plenty of fluids (more than 2,500 mL per day), especially water;
- Consume enough calcium from foods such as milk and milk products;
- Opt for calcium-rich foods to meet recommendations, rather than supplements;
- Limit soda and fruit drinks sweetened with high fructose corn syrup;
- Avoid eating too much salt and sugar.
People with kidney stones may also be advised to limit foods high in oxalates and purines.
People who are prone to kidney stones may also be advised by their health care provider to eat moderate amounts of protein and to avoid high intakes of foods high in certain compounds.3,4 These compounds include oxalates (found in plant foods such as spinach and strawberries) and purines (found in red meats, organ meats and shellfish).3,4 People should also consult a health professional before taking fish liver oil, vitamin or mineral supplements, since some supplements may increase the chances of kidney stone formation in some individuals.4
Foods high in oxalates, such as soy products, dark green leafy vegetables like spinach, rhubarb, beets, wheat bran, nuts, seeds, chocolate and strawberries contribute to raising urine oxalate levels.4,8 Low dietary calcium intake has been found to increase the formation of calcium oxalate stones.4 When higher dietary calcium is present in the digestive tract, it binds to oxalates which reduces their absorption and therefore their elimination by the kidneys.4 High salt intakes should also be avoided to reduce the risk of kidney stone formation.
Evidence on dietary calcium and milk products
There is good evidence that dietary calcium and milk products do not increase the risk of kidney stones. In fact, they are recommended to reduce the risk of kidney stone formation.3,4 Many studies have investigated different types of fluids and kidney stone risk. A 2015 dose-response meta-analysis found that higher milk intake was not associated with the risk of kidney stone formation.9 Water intake was associated with a reduced risk of kidney stones.
Prospective analyses of the Health Professionals Follow-up and Nurses’ Health Studies examined the association between dietary calcium and the risk of developing symptomatic kidney stones over 56 years of follow-up.10 Higher dietary calcium from either dairy or non-dairy sources was associated with significantly lower kidney stone risk.
The 2020 meta-analysis that explored the evidence on a wide range of dietary factors identified dietary calcium and a DASH-style diet among the factors associated with a reduced risk of kidney stones.6 However, it is important to note that this review also reported that some studies suggest that, contrary to dietary calcium from food sources, calcium supplements (especially when taken with vitamin D) may be associated with an increased risk of kidney stones.
While more research is needed on calcium supplements, kidney foundations in both Canada and the U.S. caution that some calcium supplements (which often contain vitamin D) may increase the risk of kidney stones.1,4 They therefore suggest that food sources are preferable. Thus, it’s best for people to check with their health care professional before taking supplements.
Understanding the role of dietary calcium in kidney stones
The bottom line is there’s good evidence that higher dietary calcium from food sources does not lead to kidney stones. In fact, sufficient dietary calcium intake, from foods such as milk products, is one of the key evidence-based dietary strategies recommended to help reduce the risk of kidney stones.3,4 The Canadian Urological Association and the U.S. National Kidney Foundation recommend calcium intakes of 1000 to 1200 mg per day (which is in line with the Recommended Dietary Allowance recommendations for adults) to help prevent kidney stones.4,5 Consuming 3 daily servings of milk products, such as milk, yogurt and cheese, which are reliable sources of calcium, is a good way to meet these daily calcium recommendations.4
- Kidney Foundation. 2020. Kidney stones. www.kidney.ca. Accessed October 22, 2021.
- National Kidney Foundation. 2021. Kidney stones. www.kidney.org. Accessed September 22, 2021.
- National Kidney Foundation. 2021. Calcium oxalate stones. www.kidney.org. Accessed October 22, 2021.
- National Kidney Foundation. 2021. Kidney stone diet plan and prevention. www.kidney.org. Accessed October 22, 2021.
- Dion M et al. CUA guideline on the evaluation and medical management of the kidney stone patient – 2016 update. CUAJ 2016;10:E347-358.
- Lin BB et al. Dietary and lifestyle factors for the primary prevention of nephrolithiasis: a systematic review and meta-analysis. BMC Nephrology 2020;21:267.
- Wang Z et al. Effect of dietary treatment and fluid intake on the prevention of recurrent calcium stones and changes in urine composition: A meta-analysis and systematic review. PLoS One 2021;16(4):e0250257.
- Finkielstein VA and Goldfarb DS. Strategies for preventing calcium oxalate stones. CMAJ 2006;174:1407-1409.
- Xu C et al. Self-fluid management in prevention of kidney stones: A PRISMA-compliant systematic review and dose-response meta-analysis of observational studies. Medicine (Baltimore) 2015;94:e1042.
- Taylor EN and Curhan GC. Dietary calcium from dairy and non-dairy sources and risk of symptomatic kidney stones. J Urol 2013;190:1255-1259.