Evening primrose oil supplementation increases citraturia and decreases other urinary risk factors for calcium oxalate urolithiasis

PURPOSE: We investigated the effects of gamma-linolenic acid (an omega-6 polyunsaturated fatty acid) in the form of evening primrose oil on calcium oxalate urinary stone risk factors in 2 ethnic groups. MATERIALS AND METHODS: Eight black and 8 white healthy male subjects ingested 1,000 mg evening primrose oil (Natrodale, Kuils River, South Africa) daily for 20 days while following a free diet. Arachidonic acid content was determined by a dietary questionnaire. On days 0, 10 and 20, and 4 days after protocol 24-hour urine samples were collected. Samples were analyzed using routine assays. RESULTS: Citraturia increased significantly in each group. Urinary oxalate showed a tendency to decrease in black subjects. Calciuria and the Tiselius risk index decreased significantly in each group. Carryover effects were observed. CONCLUSIONS: To our knowledge increased citraturia has not been previously reported for any essential fatty acid. We hypothesize that evening primrose oil inhibits lipogenesis, thereby decreasing citrate consumption. For the decrease in oxaluria we suggest that evening primrose oil alters membrane fatty acid composition, thereby inhibiting the modulation of protein kinases that lead to hyperoxaluria. In regard to decreased calciuria we suggest that evening primrose oil modulates delta-5 and/or delta-6-desaturase, thereby inhibiting the production of arachidonic acid and prostaglandin E2, which influence calciuria. The different response in the 2 groups with respect to oxaluria confirms previously reported differences in sensitivity toward supplemental ingestion. Data suggest that evening primrose oil supplementation should be investigated as a possible conservative treatment for calcium oxalate urolithiasis.