Turmeric's modest kidney-stone factor
Turmeric makes for an interesting supplement, but if you are prone to kidney stones you may be better off not taking it, write researchers from the US department of agriculture in the American Journal of Clinical Nutrition. They claim that turmeric contains too much oxalate.
Kidney stones come in all shapes and sizes, but kidney stones consisting largely of oxalate are relatively common. That is why nutritionists advise people who easily get kidney stones to exclude large dietary sources of oxalic acid from their diet.
The average amount of oxalic acid in 100 g spinach is about 100 mg, but it can be as high as 400 or even 1000 mg.
Kidney-stone sufferers are also better off avoiding rhubarb. One hundred grams of rhubarb contains 40-50 mg oxalic acid.
The researchers wanted to know whether cinnamon and turmeric were also risky for people who are more likely to develop kidney stones. They got 11 test subjects to take 3 g a day of cinnamon or turmeric for 4 weeks. These daily doses contained 55 mg oxalate. During the experiment the researchers measured how much oxalate the subjects retained.
Cinnamon turned out to be a relatively inefficient oxalate source, the Americans discovered, but turmeric was. This is probably because the oxalates in cinnamon do not dissolve easily and the body therefore doesn't absorb them easily, whereas the oxalates in turmeric are easily soluble.
The table below summarises the results of the experiment.
The advice for people who are prone to kidney stones is to limit their oxalate intake to 50 mg per day. Turmeric consumption is therefore not advisable for this group. The chance that healthy people develop problems from the oxalates in turmeric is small, based on the studies available.
In 2000 urologists at Wake Forest University made an estimate of the amount of oxalates we consume on a daily basis. [Kidney Int. 2000 Apr; 57(4): 1662-7.]
The table below is from this article.
As you can see, 100 g chocolate is just as risky as 3 g turmeric. Total oxalate intake varied in 5 subjects from 44 to 352 mg per day. The average intake was 152 mg. The amount you get from taking turmeric doesn't add much to this amount.
The study published in the American Journal of Clinical Nutrition prompted the manufacturer Sabinsa to take a look at the composition of its own turmeric extract Curcumin C3-Complex. [Kidney Int. 2000 Apr;57(4):1662-7.] In January 2009 Sabinsa published the results.
According to Sabinsa turmeric does indeed contain a high level of oxalates, but their extracts hardly contain any.
Am J Clin Nutr. 2008 May;87(5):1262-7.
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