Human semen quality (ie, sperm count and concentration) has declined worldwide,1 and this decrease is greater in certain geographic regions, specifically in developed and industrialized countries.2 Current data suggest that this decline is associated with environmental and lifestyle factors, such as pollution, smoking, alcohol consumption, lack of physical activity, stress, and unhealthy diets.
The evidence supporting an association of diet with sperm quality is growing very rapidly. In fact, dozens of observational studies have concluded that diets rich in foods such as fish, shellfish and seafood, poultry, cereals, vegetables and fruits, low-fat dairy, and skim milk were positively associated with several sperm quality parameters.3 In the case of specific foods, data come primarily from observational studies; however, in case of nutrients, the evidence comes more from randomized clinical trials (RCTs), sometimes of doubtful statistical power. To overcome this issue and to assess the precise association of nutrients with sperm quality parameters, a 2018 meta-analysis was published.4 This study found that the administration of ω-3 fatty acid supplements (ie, 1 g/d of docosahexaenoic acid and 1 g/d of eicosapentaenoic acid for 10-32 weeks) improved total sperm count (mean difference, 18.70 × 106 spermatozoa; 95% CI, 16.89 × 106 to 20.51 × 106 spermatozoa), sperm concentration (mean difference, 10.98 × 106 spermatozoa/mL; 95% CI, 10.25 × 106 to 11.72 × 106 spermatozoa/mL), total motility (mean difference, 7.55%; 95% CI, 7.09% to 8.01%), and morphology (mean difference, 0.91%; 95% CI, 0.69% to 1.13%). However, these results must be cautiously interpreted because of the limited sample size of the meta-analyzed studies.5,6 Although RCTs represent the cornerstone of evidence-based medicine, when the observational evidence is not well determined, a well-designed RCT is extremely difficult to conceive.
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Salas-Huetos A. More Evidence of the Association of Diet With Human Testicular Function—Fish Oil Supplements. JAMA Netw Open. 2020;3(1):e1919569. doi:10.1001/jamanetworkopen.2019.19569
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