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Turmeric's modest kidney-stone factor

Turmeric's modest kidney-stone factor
Turmeric makes for an interesting supplement, but if you are prone to kidney stones you're better off not taking it, write researchers from the US department of agriculture in the American Journal of Clinical Nutrition. They claim that turmeric supplements contain too much oxalate.

Kidney stones are made up for 80 percent of oxalate. [Structural formula of calcium oxalate shown here.] That's why nutritionists advise people with kidney stones to avoid foods that contain oxalic acid, like spinach. 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 supplements 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. The daily dose contained 55 mg oxalate. During the experiment the researchers measured how much oxalate the subjects retained. The table below summarises the results of the experiment.

Turmeric's modest kidney-stone factor

Supplements containing cinnamon do not cause problems, but turmeric supplementation can do. 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 advice for people who are prone to kidney stones is to limit their oxalate intake to 50 mg per day. Turmeric supplements are 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 the article.

Turmeric's modest kidney-stone factor

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 supplements 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. [] In January 2009 Sabinsa published the results.

Turmeric's modest kidney-stone factor

According to Sabinsa turmeric does indeed contain a high level of oxalates, but their extracts hardly contain any.

Not all supplements manufacturers that put Sabinsa's extract in their products publish this on their labels. But if you see the text that the turmeric extracts used are "standardized to contain 95 percent curcuminoids", you can assume that your supplement contains Sabinsa-made extracts.

Am J Clin Nutr. 2008 May; 87(5): 1262-7.

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