Summary
Defects in male sperm health and production are a major contributor to infertility issues. DHA has been shown to be a pivotal component of sperm cells. Accordingly, insufficient levels of DHA can contribute to infertility. Studies indicate that men who enrich their diet with DHA supplementation show an increase in positive indicators of sperm health and function. 
 
Introduction
Infertility affects roughly 15% of couples that are of reproductive age, with up to 50% of these cases resulting from male infertility. Additionally, a worldwide decline in sperm quality is reported. Altered dietary habits, such as a decrease in consumption of poly-unsaturated fatty acids like DHA, are a suspected major contributory factor to this decline of male fertility. Sperm cells, along with neurons and photoreceptor cells, have the highest DHA content of human cell types. This high sperm DHA content is pivotal, as insufficient levels of DHA are detrimental to sperm cell health and function.

Male fertility is dependent on healthy and functioning sperm cells, the conditions of which are measured by certain indicators. These are total sperm count, sperm concentration, sperm cell motility, morphology of the sperm cells and DNA integrity in the sperm cells. Established reference lower limits for these indicators of sperm health and function exist, various infertility conditions are defined as a failure to meet one or more of these lower limits. Sperm cell DNA fragmentation (loss of DNA integrity) is reported to contribute to many infertility conditions. One example of these conditions is called asthenozoospermia, where the threshold of sperm cells with normal motility is not met. Furthermore, this condition is associated with higher levels of DNA fragmentation. Research has pointed towards a beneficial role of DHA supplementation for indicators of sperm health and function, which are discussed below. 
 
Research findings
In a 2016 study, Andersen and colleagues investigated the relation between DHA levels in sperm and male fertility indicators. They found that sufficient sperm DHA levels are critical for sperm health and function (Andersen et al., 2016). Namely, sperm DHA levels were found to be positively correlated with  sperm concentration, vitality, motility, healthy morphology and total sperm count. Furthermore, higher sperm DHA levels were correlated with lower sperm DNA fragmentation, meaning that higher DHA levels have a positive effect on the integrity of the DNA in sperm cells. 
 
Men suffering from asthenozoospermia (poor sperm motility) have lower sperm DHA levels than men who do not suffer from asthenozoospermia (Conquer et al., 2000). A study report by González-Ravina and colleagues concluded that DHA supplementation with 1000 or 2000mg/day for one month significantly increased sperm motility in men with and without infertility issues. This effect was especially apparent in asthenozoospermic men (González-Ravina et al., 2018). 
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In a study setup where male participants were given either 1,500mg/day of DHA or a placebo for 10 weeks, the DHA group showed a positive effect on certain sperm quality indicators. The groups that received DHA had a higher DHA concentration. This resulted in improvements in total antioxidant capacity of sperm cells, resulting in improved DNA integrity (Martínez-Soto et al., 2016). 
 
Conclusions
The studies discussed above indicate that sperm DHA levels are a good indicator of sperm health and function. In agreement with this, men that suffer from infertility issues such as asthenozoospermia showed an increase in sperm DHA levels after taking DHA supplementation. This led to a consequent increase of positive indicators of sperm health and function, such as a decrease in sperm cell DNA fragmentation. This decrease in sperm cell DNA fragmentation as a result of DHA supplementation was also reported in other studies. In conclusion, DHA supplementation can help ensure that sperm cells have sufficient levels of DHA, which is critical for their health and function, contributing positively to male fertility.  
 
References
Andersen, J. M., Rønning, P. O., Herning, H., Bekken, S. D., Haugen, T. B., & Witczak, O. (2016). Fatty acid composition of spermatozoa is associated with BMI and with semen quality. Andrology, 4(5), 857–865. https://doi.org/10.1111/andr.12227
 
Conquer, J. A., Martin, J. B., Tummon, I., Watson, L., & Tekpetey, F. (2000). Effect of DHA supplementation on DHA status and sperm motility in asthenozoospermic males. Lipids, 35(2), 149–154. https://doi.org/10.1007/BF02664764
 
González-Ravina, C., Aguirre-Lipperheide, M., Pinto, F., Martín-Lozano, D., Fernández-Sánchez, M., Blasco, V., Santamaría-López, E., & Candenas, L. (2018). Effect of dietary supplementation with a highly pure and concentrated docosahexaenoic acid (DHA) supplement on human sperm function. Reproductive Biology, 18(3), 282–288. https://doi.org/10.1016/j.repbio.2018.06.002
 
Martínez-Soto, J. C., Domingo, J. C., Cordobilla, B., Nicolás, M., Fernández, L., Albero, P., Gadea, J., & Landeras, J. (2016). Dietary supplementation with docosahexaenoic acid (DHA) improves seminal antioxidant status and decreases sperm DNA fragmentation. Systems Biology in Reproductive Medicine, 62(6), 387–395.
https://doi.org/10.1080/19396368.2016.1246623