Clinical Evidence that Turmeric Could Cause Hyperoxaluria
Both turmeric and cinnamon are spices high in oxalate. These spices are often taken as supplements in higher amounts than might be consumed in a typical diet. This prompted researchers from the Department of Family and Consumer Sciences at the University of Wyoming to look into the effects of these supplements on urine oxalate levels. To determine this, they conducted a small clinical study to see how much oxalate from turmeric and cinnamon supplements would be absorbed. (i.67, 82)
The turmeric supplements used in the study contained 19.69 mg of oxalate per gram of turmeric. Taking them would easily exceed the ADA's recommended maximum daily intake of oxalate. To put this in a dietary perspective, spinach (considered an oxalate-rich food) contains about 7.5 mg of oxalate per gram. (i.67, 82)
Eleven healthy participants were randomly assigned to take either 3.0 g/day of cinnamon or 2.8 g/day of turmeric for four weeks. They were also told to eat only a specific low-oxalate diet for the 24-hour period prior to each day their urine was tested. The researchers measured participants' urine oxalate levels two, four, six and twenty-two hours after taking the supplements. (i.67)
After adjusting for the oxalate normally synthesized and excreted by the body, they determined the oxalate absorption levels for both cinnamon and turmeric. Results showed that the participants absorbed 8.2% of the oxalate in turmeric and 2.6% of the oxalate in cinnamon. Because of this, the researchers warned that turmeric supplements could increase the risk of kidney stones in people who are prone to them. (i.67)
What Do Doctors Say About Oxalate Intake?
So turmeric has high amounts of soluble, absorbable oxalate. Does this mean people who develop kidney stones should avoid turmeric supplements? Some medical doctors and experts suggest the answer might be no. They indicate that warnings about eating oxalate-rich foods and the ADA daily intake limit of 50 mg/day may be unwarranted, for several reasons: (i.81, 82)
ADA recommended maximum intake of 50 mg/day is not an accepted standard. For example, the National Kidney & Urologic Diseases Information Clearinghouse gives no maximum daily oxalate limit in their fact sheet provided for kidney stone prevention. And the doctors from the University of Chicago Medical Department suggest that restricting oxalate intake to 100 mg/day or less (double the ADA standard) may be prudent if a person has hyperoxaluria. (i.84, 85)
Evidence suggests other dietary factors are more relevant than oxalate content. Some doctors and dietitians recommend avoiding oxalate-rich foods and spices to prevent kidney stones. However, some studies indicate this may not be the best advice. In fact, there is evidence that contradicts these recommendations. One study showed that vegetarians who consume high levels of oxalate-containing foods are actually less likely to develop kidney stones. (i.81, 86)
Clinical trial results indicate that other dietary factors are more important than simply avoiding foods rich in oxalates. These factors include limiting animal protein, taking in enough calcium, and increasing fluids. One example of the impact of other dietary factors comes from a randomized, controlled, long-term clinical trial involving men prone to kidney stones. Some participants followed a low calcium diet. Others ate a diet that limited animal protein and sodium but kept normal calcium intake levels. Those who ate less meat and limited salt intake had almost 50% less kidney stone recurrences than those who followed a restricted calcium diet. Oxalate intake for both groups was the same—about 200 mg/day—4 times the ADA maximum. (i.81, 86)
In addition, a 5-year randomized trial showed that increased fluid intake (primarily with water and low-carbohydrate beverages) significantly reduced recurrence of kidney stones. (i.81, 86)
Calcium counteracts high oxalate food content. As suggested above in the clinical trial comparing normal and reduced calcium intakes, a review of multiple studies showed that the balance of calcium and oxalate is more predictive of kidney stone formation. In fact, increasing calcium intake can offset extremely high consumption of oxalate-rich foods. Calcium's counteracting effect was even noted in the clinical trial comparing oxalate absorption from cinnamon and turmeric. (i.67, 83)
Turmeric's Protective Effects May Outweigh Risks
People at risk of kidney stones should consult with their doctor regarding dietary and other changes that may increase that risk of forming stones. However, while turmeric is rich in absorbable oxalate, other dietary factors can offset high dietary consumption of oxalate. Turmeric's health benefits may outweigh any increased risk for developing kidney stones. (i.87)
According to some research, these benefits include preventing certain types of kidney stones. Recent lab results suggest that curcumin (the primary polyphenol in turmeric) could actually help prevent dangerous (but rare) struvite kidney stones from developing. (i.87)
Additional animal studies indicate that the curcumin in turmeric can prevent injuries to kidney tissue caused by shock wave lithotripsy. This is a commonly used treatment to break up kidney stones too large to pass through the urinary tract. Rats given oral doses of curcumin before and after shock wave lithotripsy had far less scarred or dead tissue than the group not given curcumin. The researchers in this study attributed the positive results to curcumin's antioxidant effects against free radicals induced by the shock wave treatment. (i.88)
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