The male reproductive system is designed to produce, store, and convey sperm and the fluid that protects, nourishes and transports it (seminal fluid). Even slight changes in sperm concentration, motility, morphology, or the medium that protects it can lead to infertility.
Since 1970, there has been a steady — and alarming — decline in sperm count recorded in Western countries.
A comprehensive meta-analysis has shown a decline of 50-60% in sperm counts in general male population (not selected by fertility) in North America, Europe and Australia during 1973–2011. This decline in male reproductive health has serious implications beyond fertility concerns .
Oxidative stress— sometimes perceived as an imbalance between reactive oxygen species (ROS) and antioxidants — causes a decrease in viability and motility of the sperm .It is believed to be one of the major causes of male infertility. In fact, about 30%-40% of infertile men tested in a study were shown to have elevated levels of ROS in their seminal plasma.
The formation of ROS can be stimulated by pollutants cigarettes, alcohol, heavy metals, drugs, or radiation. The body also produces ROS during normal metabolic processes.
Reactive oxygen species must be below a certain level for sperm to function. High levels of ROS have adverse effects on the structural and functional integrity of the sperm and can cause infertility through not only by lipid peroxidation or DNA damage but deactivating key enzymes and oxidizing critical proteins in spermatozoa. Sperm cells are especially susceptible to oxidative insult, as they lack oxidative a cytoplasmic-enzyme repair system.
Astaxanthin is one of the most powerful antioxidants in nature, more potent than tocopherol (vitamin E), vitamin C, and lycopene. Astaxanthin is easily absorbed and widely distributed to many tissues. Due to its unique structure, situated through the cell’s protective lipid bilayer, it enables protection of the cells from both internal and external oxidative stressors.
The effect of astaxanthin on sperm cells and male fertility was shown in various pre-clinical and clinical studies.
Cohmaire, et al. (2005) evaluated the effect of conventional fertility combined with either astaxanthin or placebo on 30 men having been clinically diagnosed as infertile for a period of at least 12 months. Various factors related to sperm parameters, ROS, and multiple hormones were monitored before and after the consumption of either 16mg astaxanthin or placebo for 12 weeks. The outcomes exhibited an increase in sperm concentration by 34%, ROS decrease by 75%, and the number spermatozoa firmly attached per oocytes was increased by 300%. Furthermore, total pregnancy success rate for the astaxanthin group was 54.5% in comparison to 10.5% in the placebo group.
For a sperm to fertilize an egg, it must undergo a series of changes upon meeting the egg. These changes are mediated by the discharge of reactive oxygen species in the sperm in the right amount, at the right time. Infertile men have been shown to have increased oxidative stress in the seminal fluid, and an increase in abnormal sperm that cannot fertilize an egg. Incubation of human sperm cells with astaxanthin improved parameters related to sperm’s ability to make the changes needed to fertilize an egg, and increased the number of fertilization-ready sperm in a sample.
In multiple pre-clinical studies, astaxanthin showed better sperm health parameters. An animal study demonstrated a total sperm count increase of 14%, with viability increased 50% and a significant decrease in the percentage of abnormal sperm.  Other animal studies, conducted on subjects fed a high-fat diet plus a combination of astaxanthin and vitamins A and E showed also improved sperm parameters.[7, 8]
Evidence from further animal studies, in vitro studies, and other human clinical studies indicate that astaxanthin could have a beneficial effect on sperm quality parameters due to its strong anti-oxidative activity. In order to further evaluate the effect of astaxanthin on male infertility, additional human studies should be performed.