Milk Products and Kidney Stones
Data from dietary intervention studies, systematic reviews and meta-analyses indicate that milk products in general and dietary calcium in particular may reduce the risk of developing kidney stones.
Kidney stone formation, also known as nephrolithiasis, affects about 1 in 10 Canadians and increases the risk of chronic kidney disease.1 Kidney stones are small, hard stones made of mineral and acid salt crystals, which are formed inside the kidneys.
Calcium oxalate stones are the most common type of kidney stones. The main mechanism involves the calcium/oxalate balance in urine. Foods high in oxalates, such as rhubarb, soy products, peanuts and black tea, contribute to raising urine oxalate levels.2,3 High intakes of protein and salt and low intakes of fluids, potassium and magnesium also promote kidney stones.4
A number of studies have been conducted on the association between milk products and kidney stones. The evidence indicates that consuming milk and milk products does not increase the risk of kidney stone formation. In fact, increasing dietary calcium from foods such as milk and milk products is recommended to prevent kidney stones.3,5
Evidence on milk and milk products
A 2015 dose-response meta-analysis investigated the association between different types of fluids and the risk of kidney stones. The analysis consisted of 10 prospective cohort and 5 case-control studies, for a total of 351,081 participants.6
- Higher milk intake was not associated with the risk of kidney stone formation;
- Each 500 mL increase in water intake was associated with a 7% reduced risk of kidney stones.
Taylor and Curhan conducted prospective analyses of the Health Professionals Follow-up Study (n = 30,762 men), the Nurses’ Health Study (n = 94,164 women) and the Nurses’ Health Study II (n = 101,701 women). The authors examined the association between non-dairy dietary calcium and dairy calcium and the risk of incident symptomatic kidney stones over 56 years of follow-ups.7
- Higher dietary calcium from either dairy or non-dairy sources was independently associated with lower kidney stone risk;
- The highest (~816-937 mg/day) compared to the lowest (143-181 mg/day) quintile of dairy calcium was associated with a 17% to 24% reduced kidney stone risk;
- The highest (~439-460 mg/day) compared to the lowest (256-272 mg/day) quintile of non-dairy dietary calcium was associated with an 18% to 29% reduced kidney stone risk.
Evidence on calcium
A systematic review of randomized trials and dietary interventions examined the evidence on diet, fluid and supplement intake for secondary prevention of nephrolithiasis. The study concluded that “limited data suggest possible benefit from dietary calcium.”8
In a prospective cohort study entitled The Study of Osteoporotic Fractures, Sorensen et al. examined data from 7,982 women aged 65 years and older to assess the impact of calcium intake on kidney stones.9
- Those with increased dietary calcium intake (>565 vs. <216 mg/day) were 45% to 54% less likely to have kidney stones;
- Women who had used calcium supplements were 21% to 44% less likely to have a history of kidney stones;
- The authors of the study concluded that “dietary and supplemental calcium decrease fractional calcium absorption and may protect against nephrolithiasis.”
Hypercalciuria (or excessive urinary calcium excretion) is the most common metabolic abnormality associated with kidney stones.10 However, urinary oxalate has been reported to be a more powerful risk factor for stones than urinary calcium.11
Decreasing dietary calcium intake is not a recommended strategy for the prevention of calcium stones.4,10 Low dietary calcium intake has been found to increase calcium oxalate stone formation. When dietary calcium is limited, oxalate is more available for intestinal absorption, leading to greater urinary oxalate excretion and the possibility of kidney stone formation. Conversely, increased dietary calcium intake inhibits intestinal oxalate absorption by binding to dietary oxalate and forming calcium oxalate, thereby reducing oxalate excretion.3,10
Furthermore, low calcium diets do not appear to be successful in reducing calciuria. In addition, limiting calcium from dairy products may lead to increases in other animal proteins (meat, fish, poultry), which increase calciuria and the risk of kidney stones.4
There is good evidence indicating that milk products and dietary calcium do not increase the risk of kidney stones. In fact, they are recommended to reduce the risk of kidney stone formation.
Randomized controlled trials of high versus low intakes of milk products and dietary calcium versus calcium supplements are needed to provide more definitive answers.
- The Kidney Foundation of Canada. 2003. Kidney stones. www.kidney.ca. Accessed February 19, 2016.
- National Kidney Foundation. 2016. Kidney stones. www.kidney.org. Accessed February 19, 2016.
- Finkielstein VA and Goldfarb DS. Strategies for preventing calcium oxalate stones. CMAJ 2006;174:1407-1409.
- Borghi L et al. Dietary therapy in idiopathic nephrolithiasis. Nutr Rev 2006;64:301-312.
- Dietitians of Canada. 2015. Healthy eating guidelines for prevention of recurrent kidney stones. www.pennutrition.com. Accessed February 19, 2016.
- 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.
- Fink HA et al. Diet, fluid, or supplements for secondary prevention of nephrolithiasis: a systematic review and meta-analysis of randomized trials. Eur Urol 2009;56:72-80.
- Sorensen MD et al. Impact of calcium intake and intestinal calcium absorption on kidney stones in older women: The Study of Osteoporotic Fractures (SOF). J Urol 2012;187:1287-1292.
- Sorensen MD. Calcium intake and urinary stone disease. Transl Androl Urol 2014;3:235-240.
- Heaney RP. Calcium supplementation and incident kidney stone risk: a systematic review. J Am Coll Nutr 2008;27:519-527.