Diabetes does not appear to significantly reduce sperm count or concentration, but it does harm sperm quality in ways that matter for fertility. A large meta-analysis of observational studies found no meaningful difference in total sperm count between diabetic and non-diabetic men. Where diabetes does real damage is to sperm motility (how well sperm swim), semen volume, and the genetic integrity of sperm cells. So while the raw number of sperm may look normal on a semen analysis, the sperm themselves are less likely to function properly.
Sperm Count Stays Stable, but Motility Drops
The distinction between sperm count and sperm quality is important here. A meta-analysis pooling data from multiple observational studies found that diabetes did not influence total sperm count. A 2025 study comparing men with type 2 diabetes to a control group confirmed this: sperm concentration was virtually identical between the two groups (about 52.8 million per milliliter in the diabetic group versus 53.0 million in healthy controls).
Motility is a different story. The same meta-analysis found that diabetic men had roughly 14 percentage points fewer motile sperm than non-diabetic men. That’s a substantial gap. The 2025 study showed a similar pattern, with average motility of 23% in the diabetic group compared to 29.7% in controls. Semen volume was also lower in diabetic men, by about two-thirds of a milliliter on average. Less volume means fewer total sperm delivered per ejaculation, even if concentration looks normal.
How High Blood Sugar Damages Sperm
Persistently elevated blood sugar creates an excess of reactive molecules (free radicals) that overwhelm the body’s natural antioxidant defenses. Sperm cells are particularly vulnerable to this kind of damage because they have limited ability to repair themselves once mature. In this oxidative environment, sperm cells can undergo a process of self-destruction that fragments their DNA.
Research has shown that even diabetic men whose standard semen parameters look normal still carry significantly higher levels of DNA damage in their sperm, both in the cell’s energy-producing structures and in its nucleus where genetic material is stored. This hidden damage can reduce fertilization success and may affect embryo development, which is why a normal-looking semen analysis doesn’t always tell the full story for diabetic men trying to conceive.
Hormonal Changes That Affect Sperm Production
Type 2 diabetes disrupts the hormonal chain of command that drives sperm production. Insulin resistance and elevated insulin levels suppress the brain signals (luteinizing hormone and follicle-stimulating hormone) that tell the testicles to produce testosterone and generate sperm. Lower testosterone is both a consequence and a contributor to testicular damage in diabetic men.
The testosterone drop happens at the cellular level. The cells in the testicles responsible for making testosterone (Leydig cells) sustain direct damage from the diabetic environment, reducing their ability to produce the hormone. This creates a cycle: less testosterone means less robust sperm production, and the metabolic dysfunction of diabetes keeps driving the problem. Some research suggests that weight-loss interventions like bariatric surgery can partially reverse this by reducing insulin resistance, which in turn allows hormone levels to recover.
Nerve Damage Can Redirect Ejaculation
Diabetes can cause a less obvious fertility problem through nerve damage. During normal ejaculation, a small muscle at the bladder neck contracts to close it off, directing semen forward and out. This contraction is controlled by nerves from the autonomic nervous system, the same network that diabetes frequently damages.
When those nerves stop working properly, the bladder neck doesn’t seal shut during orgasm, and semen travels backward into the bladder instead of forward. This is called retrograde ejaculation. A man with this condition typically notices that very little or no fluid comes out during climax, even though the sensation of orgasm feels normal. The sperm end up in the urine rather than being delivered. This doesn’t mean sperm aren’t being produced; it means they’re being sent to the wrong place.
Blood Sugar Control Makes a Measurable Difference
How well you manage your blood sugar directly correlates with how much damage your sperm sustain. A study examining the effect of diabetic blood plasma on sperm found that higher HbA1c levels (a marker of average blood sugar over the previous two to three months) caused progressively worse outcomes. Men with HbA1c at or above 10% showed the most severe drops in sperm swimming speed and the highest levels of oxidative damage to sperm cell membranes. At that level, the oxidative damage to sperm was actually worse than what researchers observed when they deliberately exposed sperm to hydrogen peroxide in the lab.
The encouraging side of this finding is that tighter glucose control appears to be protective. Bringing blood sugar closer to normal reduces the oxidative assault on sperm and may allow some recovery of motility and genetic integrity. Current evidence supports the idea that glucose-lowering treatment can help reverse diabetes-related sperm quality problems, though the benefits depend on the specific approach used.
Metformin’s Complicated Role
Metformin, the most commonly prescribed medication for type 2 diabetes, has a mixed track record when it comes to male fertility. By improving blood sugar control, it should theoretically help protect sperm. But the direct effects of the drug on the reproductive system are not clearly positive. One small clinical trial found that 12 weeks of metformin in obese men was associated with a significant reduction in both sperm count and sperm activity. Some studies have also linked metformin use to lower testosterone levels in men with type 2 diabetes.
Other research points in the opposite direction, suggesting metformin may improve testosterone and hormonal signaling in obese men with metabolic syndrome. The current consensus is that metformin’s effects on male reproduction are contradictory and likely depend on individual factors like weight, baseline hormone levels, and duration of use. If you’re taking metformin and concerned about fertility, this is worth discussing with your care team, as alternative glucose-lowering options exist.