BONN, GERMANY. Kidney stones, a painful urologic disorder, have beset humans for at least 7000 years. It is estimated that about 5% of the population in the US are affected, most of them men of Caucasian origin. Kidney stones, in 75% of cases, consist of calcium oxalate which is excreted in the kidneys from urine supersaturated with calcium and oxalic acid. A tendency to kidney stone formation is often inherited and a first episode of stone formation is often followed by others.
A team of researchers at Bonn University now reports that supplementing with fish oil can materially reduce the risk of supersaturation of calcium oxalate in the urine and thus reduce the risk of kidney stones. Their trial included 7 women and 8 men with a mean age of 28 years (range of 21 to 34 years) with no history of stone formation. After consuming a standardized diet for 5 days to establish a baseline, the study participants added 3 fish oil capsules a day to their diet for a 30-day period. The capsules provided a daily intake of 900 mg of EPA (eicosapentaenoic acid) and 600 mg of DHA (docosahexaenoic acid). At the end of the 3-day follow-up period, the average daily urinary oxalate excretion had dropped by 14% (from 0.277 mmoL/24 hrs to 0.238 mmoL/24 hrs) corresponding to an estimated 23% reduction in the risk of forming calcium oxalate stones. There was no significant change in calcium excretion.
The German researchers speculate that the beneficial effects of fish oils are related to their ability to replace arachidonic acid in cell membranes with a resulting decrease in urinary excretion of oxalate.
Siener, R, et al. Effect of n-3 fatty acid supplementation on urinary risk factors for calcium oxalate stone formation. Journal of Urology, Vol. 185, February 2011, pp. 719-24