Women with PMS often have low blood levels of omega-3 fatty acids (Am J Obstet Gynecol, 1984; 150: 363-6). This may be due to a genetic glitch that impairs conversion of linoleic acid (LNA) to gamma-linolenic acid (GLA) (J Nutr Med, 1991; 2: 259-64).
Evening primrose, blackcurrant and borage oils contain GLA. Evening primrose oil (3-4 g/day) has been extensively studied as a potential way to reduce symptoms of PMS and most trials, though not all, have found it to be beneficial (Control Clin Trials, 1996; 17: 60-8; J Reprod Med, 1985; 30: 149-53; Rec Adv Clin Nutr, 1986; 2: 404-5). Evening primrose may be particularly effective for breast tenderness (Br J Clin Pract, 1992; 46: 161-4), but it needs to be taken for several months before any benefits can be seen.