AbstractThe effects of supplementation with docosahexaenoic acid (DHA) on DHA levels in serum, seminal plasma, and sperm of asthenozoospermic men as well as on sperm motility were examined in a randomized, double‐blind, placebo‐controlled manner. Asthenozoospermic men (n=28; ≤50% motility) were supplemented with 0, 400, or 800 mg DHA/d for 3 mon. Sperm motility and the fatty acid composition of serum, seminal plasma, and sperm phospholipid were determined before and after supplementation. In serum, DHA supplementation resulted in decreases in 22∶4n−6 (−30% in the 800‐mg DHA group only) and total n−6 (−6 and −12% in the 400‐ and 800‐mg DHA groups, respectively) fatty acids. Increases were noted in DHA (71 and 131% in the 400‐ and 800‐mg DHA groups, respectively), total n−3 fatty acids (42 and 67% in the 400‐ and 800‐mg DHA groups, respectively), and the n−3/n−6 ratio (50 and 93% in the 400‐ and 800‐mg DHA groups, respectively). In seminal plasma, DHA supplementation resulted in a decrease in 22∶4n−6 (−31% in the 800‐mg DHA group only) and an increase in the ratio of n−3 to n−6 (35 and 33% in the 400‐ and 800‐mg DHA groups, respectively). There were insignificant increases in DHA and total n−3 fatty acids. In sperm, decreases were noted in 22∶4n−6 (−37 and −31% in the 400‐and 800‐mg DHA groups, respectively). There were no other changes. There was no effect of DHA supplementation on sperm motility. The results show that dietary DHA supplementation results in increased serum‐ and possibly seminal plasma—phospholipid DHA levels, without affecting the incorporation of DHA into the spermatozoa phospholipid in asthenozoospermic men. This inability of DHA to be incorporated into sperm phospholipid is most likely responsible for the observed lack of effect of DHA supplementation on sperm motility.