Short answer: Diabetes affects male fertility through three separate routes: it damages sperm DNA through oxidative stress, it causes erectile and ejaculatory problems including retrograde ejaculation, and in type 2 diabetes it disrupts testosterone. Standard semen parameters often look close to normal in men with diabetes, which is exactly why the effect gets missed. New projections presented in 2026 estimate the number of people living with type 1 diabetes will rise 29% by 2049, which makes this a growing rather than a shrinking issue for men planning a family.
Why this is becoming a bigger question
Research presented at the Annual Meeting of the European Association for the Study of Diabetes in Milan estimates that the number of people living with type 1 diabetes worldwide will rise from 9.4 million in 2025 to 12.1 million by 2049, an increase of 29%. Annual new diagnoses are projected to climb from around 530,000 to more than 605,000 over the same period.
People aged under 20 account for an estimated 42% of new cases globally. That matters here, because a diagnosis at 12 or 16 means several decades of managing the condition before a man starts thinking about children, and it means the conversation about fertility usually happens long after the conversation about insulin.
Type 2 diabetes is a larger population still, and it arrives alongside the risk factors that independently affect sperm: excess weight, insulin resistance and reduced testosterone.
What diabetes actually does to sperm
The mechanism runs through oxidative stress, which is the same pathway that makes smoking so damaging to sperm.
Persistently elevated blood glucose drives the production of reactive oxygen species. Sperm cells are unusually vulnerable to these, because their membranes are rich in polyunsaturated fatty acids and they carry very little of the cytoplasmic machinery that other cells use to repair oxidative damage. The result is damage to the membrane, which affects movement, and damage to the tightly packed DNA in the sperm head.
Elevated glucose also drives the formation of advanced glycation end products, which accumulate in the reproductive tract and add to the oxidative load.
The finding that gets missed on a standard semen analysis
Here is the part that matters most, and it is counterintuitive.
A systematic review and meta-analysis published in Andrology in 2022, covering 380 men with type 1 diabetes against 434 controls, found no significant difference in semen volume, sperm concentration or total sperm count. What it did find was a 33.6% reduction in progressive motility and a significant reduction in normal morphology.
Read that carefully. Concentration and count, the two numbers most men fixate on, came back looking fine. The parameters that describe whether sperm can actually swim and whether they are correctly formed did not.
Across the wider literature, summarised in a 2023 clinical evidence review in Andrology, the most consistent findings in men with diabetes are reduced motility and increased sperm DNA fragmentation rather than a straightforward drop in numbers.
Sperm DNA fragmentation is not measured by a standard semen analysis. A man with well-controlled numbers and poor DNA integrity will get a normal-looking report. This is one of the clearest examples of why you cannot judge sperm health by appearance or by a single headline number.
Type 1 and type 2 do not behave the same way
The two conditions affect male fertility through overlapping but distinct routes, and it is worth separating them.
Type 1 diabetes
The dominant signal is reduced progressive motility and increased DNA fragmentation, with sperm counts often within normal limits. Duration of the condition and glycaemic control appear to matter more than the diagnosis itself. Men diagnosed young who have had decades of variable control tend to show more effect than those with a shorter or better-controlled history.
Type 2 diabetes
Here the hormonal picture becomes central. Type 2 diabetes usually travels with excess weight and insulin resistance, and a meta-analysis of diabetes and obesity in relation to sperm parameters and testosterone found both associated with lower testosterone levels. Adipose tissue converts testosterone to oestrogen through the aromatase enzyme, which pushes the hormonal balance in the wrong direction for sperm production. A meta-analysis of observational studies comparing men with type 2 diabetes against non-diabetic controls found significantly reduced semen volume.
Because weight is doing much of the work in type 2, it is also the most modifiable part of the picture.
Erectile dysfunction and ejaculation problems
Neither of these shows up in a semen analysis, and both affect whether conception happens.
Erectile dysfunction is one of the most common complications of diabetes, and it arrives through two routes at once. Diabetes damages the endothelial lining of blood vessels, reducing the blood flow an erection depends on, and it damages the small nerves that carry the signal. Men with diabetes develop erectile dysfunction earlier and more often than men without it.
Retrograde ejaculation is less discussed and specific to this population. Diabetic neuropathy can affect the bladder neck muscle that normally closes during ejaculation. When it fails to close, semen travels backwards into the bladder rather than out through the urethra. The signs are a noticeably reduced or absent ejaculate volume and cloudy urine after sex. It is treatable, and sperm can usually be recovered from urine for use in assisted reproduction, but it needs to be identified first.
If your ejaculate volume has dropped markedly, that is worth raising with a clinician rather than assuming it is a normal part of ageing. Our guide on what healthy semen looks like covers what normal volume and texture actually are.
Does better glucose control improve sperm?
The honest answer is that the direct evidence is thinner than anyone would like. There are no large randomised trials showing that tightening HbA1c improves live birth rates.
What the mechanism supports is reasonable inference. If the damage runs through oxidative stress driven by elevated glucose, then reducing that exposure should reduce the damage. Sperm production runs on a cycle of roughly 72 to 74 days, so the sperm in a sample today reflects conditions in your body around three months ago. Any improvement in control will show up on that timescale rather than immediately.
The other reason to act is that the interventions overlap almost completely with what is already recommended for diabetes management. Weight loss, physical activity, stopping smoking and reducing alcohol all improve glycaemic control and all independently support sperm health. You are not being asked to do anything extra.
What to do if you have diabetes and want children
1. Test earlier than the standard 12-month threshold. The general guidance to try for a year before investigating assumes no known risk factors. Diabetes is a known risk factor. A baseline semen analysis before you start trying gives you a number to work from rather than a year of uncertainty.
2. Ask specifically about DNA fragmentation if standard results look normal. Given that concentration and count often come back within range while DNA integrity does not, a normal semen analysis is less reassuring in this context than it would be otherwise. A specialist DNA fragmentation test is available through fertility clinics.
3. Raise erectile or ejaculatory changes directly. These are common, treatable, and consistently under-reported. Reduced ejaculate volume in particular has a specific diabetic explanation that is easy to miss.
4. Work on control in the three months before trying. One full sperm production cycle is the minimum window in which improvements can show up.
5. Review your medication with your GP, not on your own. Some medications used alongside diabetes management can affect sexual function. Never stop or change a prescription without medical advice. Our guide on medication and male fertility covers how to approach that conversation.
6. Address the shared risk factors. Weight, activity, smoking and alcohol are doing work in both conditions at once. Our 10 healthy habits for male fertility is the practical version of this.
Sperm health as a window into metabolic health
There is an argument for running this in the other direction too.
Semen quality correlates with general health in ways that go well beyond fertility, and better semen quality has been linked to longer life. Poor semen parameters in a man with no known metabolic diagnosis are sometimes the first observable sign that something systemic is going on.
For men with a family history of diabetes who have not been diagnosed, that is a reasonable secondary argument for testing. You may be measuring more than your fertility.
Frequently asked questions
Does diabetes cause infertility in men?
Diabetes does not automatically cause infertility, and many men with diabetes conceive without difficulty. It does raise the risk, mainly through reduced sperm motility, increased sperm DNA fragmentation, erectile dysfunction and retrograde ejaculation. Duration of the condition and glycaemic control appear to matter more than the diagnosis alone.
Can type 1 diabetes affect sperm count?
Usually not directly. A 2022 meta-analysis of 380 men with type 1 diabetes found no significant difference in sperm concentration or total count compared with controls, but a 33.6% reduction in progressive motility and reduced normal morphology. Count is often the parameter least affected, which is why it can be falsely reassuring.
Will improving my blood sugar improve my sperm?
The mechanism supports it, since the damage runs largely through oxidative stress driven by elevated glucose, but large trials directly testing this in fertility outcomes do not exist. Any change would show up over one full sperm production cycle of around 90 days rather than immediately. The interventions involved overlap almost entirely with standard diabetes management.
What is retrograde ejaculation and how do I know if I have it?
It happens when the bladder neck fails to close during ejaculation, so semen travels into the bladder instead of out. Diabetic nerve damage is a common cause. The signs are a markedly reduced or absent ejaculate and cloudy urine afterwards. It is diagnosed by testing urine for sperm after ejaculation, and sperm can usually be recovered for use in assisted reproduction.
Should I get tested before we start trying?
With a diabetes diagnosis, yes. The usual advice to try for 12 months before investigating assumes no known risk factors. A baseline gives you information now rather than after a year, and lets you measure whether changes you make are working.
Does metformin affect sperm?
The evidence is mixed and generally reassuring, with some studies suggesting neutral or mildly positive effects through improved metabolic control. Never stop or change any diabetes medication because of fertility concerns without discussing it with your GP or diabetes team first.
The takeaway
Diabetes affects male fertility mostly through sperm movement, DNA integrity and sexual function rather than through sperm count, which is why a standard semen analysis can look normal while something is genuinely going on.
With type 1 diabetes cases projected to rise by nearly a third over the next two decades, and type 2 rates climbing alongside obesity, this is a conversation that more men will need to have and few are currently having.
If you have diabetes and you are planning a family, get a baseline before you start trying. The ExSeed home sperm test measures concentration, motility and total motile sperm count to WHO standards, and motility is the parameter this condition affects most.
This article is for information only and does not replace medical advice. Never change or stop diabetes medication without speaking to your GP or diabetes team. If you have been trying to conceive for 12 months or more, or have concerns about erectile or ejaculatory function, speak to a healthcare professional.
