Above the age of 40, motility, morphology, and DNA integrity of sperm cells demonstrably decrease. Lifestyle interventions such as weight loss are proven to help, but there is insufficient evidence for hormonal and epigenetic treatments, and some are even risky. There are no proven interventions that fully reverse age-related sperm decline.
From the age of forty, sperm quality changes noticeably. A study of more than 2,600 men found that above the age of 40, both the motility and morphology of sperm cells decline significantly. Morphology (the shape) even begins to deteriorate slightly earlier than motility. At the same time, 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: they mean that the risks increase, not that pregnancy becomes impossible.
What you can do yourself starts with body weight. Excess weight disrupts the hormonal balance, increases inflammation and oxidative stress, and has demonstrably negative effects on sperm concentration, motility, viability and DNA integrity. Weight loss and lifestyle changes are explicitly identified in the scientific literature as treatment strategies. No precise threshold is known, but the effect of obesity on sperm quality has been consistently demonstrated.
Another factor that is easily overlooked: prostatitis, an inflammation of the prostate. This is seen more frequently as men get older, and the prostate supplies a large part of the seminal fluid that supports sperm cells. Prostatitis can seriously impair sperm quality. Have this ruled out or treated if you are experiencing fertility problems.
On the subject of testosterone and hormones, it is important to highlight one commonly made mistake. As men age, testosterone production does indeed decline, and this also affects sperm production. However, simply starting to use testosterone (via gel, injections or patches) actually makes things worse: external testosterone further suppresses the body's own sperm production. Men who want to improve their fertility must not start this without medical consultation. Furthermore, testosterone treatment is contraindicated in prostate or breast cancer, severe heart failure and certain urinary tract disorders.
In the area of epigenetics (the chemical 'switching layer' on top of the DNA in sperm cells), there are indications that aging also brings about subtle changes that can influence embryo development. However, the exact mechanisms are not yet fully understood and there are as yet 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.