The evidence is strongest for weight management and the treatment of prostatitis: both are consistently supported in human studies and are explicitly identified as strategies in the literature. The testosterone pitfall is well documented and clinically relevant for men in this age group. Epigenetic interventions and experimental proteins such as SKAP2 are still at an early stage of research and have no proven application in humans. Within the limits of what is currently known, lifestyle measures and medical screening offer the best prospects.
Sperm quality changes noticeably after the age of forty. A study of more than 2,600 men found that above the age of 40 both sperm motility and morphology decline significantly, with morphology beginning to deteriorate slightly earlier than motility. On top of that, DNA damage in sperm cells increases by approximately 3 percent per year of life, which is associated with a higher risk of miscarriage and, in rare cases, congenital conditions in offspring. These are strong associations, but not a reason to panic: the risks increase, but pregnancy does not become impossible.
The most concrete lever is addressing body weight when overweight is present. Excess weight disrupts the hormonal balance, increases inflammation and oxidative stress, and has demonstrably negative effects on sperm concentration, motility, viability, and DNA integrity. The scientific literature explicitly identifies weight loss and lifestyle change as a treatment strategy. No precise threshold is known, but the effect of obesity on sperm quality has been consistently demonstrated across multiple studies.
One factor that is easily overlooked is prostatitis: an inflammation of the prostate that becomes more common as men age. The prostate provides a large proportion of the seminal fluid that supports sperm cells, and prostatitis can seriously impair sperm quality. Have this ruled out or treated if you are experiencing fertility problems.
Regarding hormones, it is important to highlight one commonly made mistake. Testosterone production does indeed decline with age, and this also affects sperm production. However, using testosterone via gel, injections, or patches actually makes things worse: external administration further suppresses the body's own sperm production. Men who want to improve their fertility must not start this without medical consultation. Moreover, testosterone treatment is contraindicated in prostate or breast cancer, severe heart failure, and certain urinary tract disorders.
In the field of epigenetics, the chemical regulatory layer on top of the DNA in sperm cells, there are indications that aging brings about subtle changes that can influence embryo development. The exact mechanisms are not yet fully understood and there are currently no proven interventions in this area. Experimental research involving a specific protein (SKAP2) showed improved motility in mouse studies and laboratory tests with human sperm, but this has no application in humans whatsoever and is purely at a research stage.
The associations between age and sperm quality are well supported by large studies. The effects of obesity and prostatitis are moderately well proven (observational studies). The warning about testosterone use is causally supported. Experimental findings (SKAP2, epigenetics) are preliminary and have no clinical application. Randomised trials on most lifestyle interventions specifically in the 40+ group are lacking.