The European Male Ageing Study found that low testosterone only earned the label when three sexual symptoms travelled together: reduced morning erections, low sexual desire, and erectile difficulty. One symptom on its own was not enough. That is a much higher bar than the internet applies, and it is the bar a specialist uses.
This is the symptom men type into a search bar at two in the morning. It is also the one where the wrong explanation costs the most, because an erection is a vascular event before it is a hormonal one.
What the study actually did
The European Male Ageing Study looked at thousands of middle aged and older men across Europe and asked a question nobody had answered properly: which symptoms genuinely track with a low testosterone level, and which are just things that happen to men as they age?
Most of the candidates fell away. Tiredness, low mood, poor concentration, aches: all common, none of them specific. What survived were three sexual symptoms, occurring together, alongside a low testosterone level.
That finding cuts in two directions and you should hear both. It means erectile change genuinely belongs in this conversation. It also means erectile change on its own, without the other two, points somewhere else.
What it usually is instead
An erection depends on blood vessels that dilate on demand and on nerves that tell them to. Anything that damages small blood vessels damages erections, usually years before it damages anything you would notice elsewhere.
High blood pressure. Diabetes and pre-diabetes. Raised cholesterol. Smoking. Excess weight. Several very common medications, including some blood pressure tablets and most antidepressants. Alcohol. Untreated sleep apnea. And anxiety, which is both a cause and a consequence and is almost never the only thing going on.
The part nobody wants to read
Erectile difficulty can be the first sign of cardiovascular disease, and it can appear before chest pain, before breathlessness, before anything shows up on a routine check.
The vessels involved in an erection are narrower than the ones supplying your heart. Narrowing shows there first.
That is not a reason to panic. It is the reason a good assessment of this symptom looks at your blood pressure, your glucose, your lipids and your weight, and does not stop at a hormone level. A man who is given testosterone for an erectile problem caused by early vascular disease has been given the wrong answer and has lost the warning that came with the question.
What testosterone does and does not do here
Testosterone drives desire more reliably than it drives erections. Men whose main complaint is that they no longer want sex, rather than that they cannot, tend to be the ones in whom the hormone is doing more of the work.
Treatment trials in older men have found improvement in sexual function overall, with the desire component moving more than the mechanical one. If the machinery is the problem, the hormone is not the fix.
Morning erections are the useful question
Clinicians ask about them for a reason. They happen during sleep, outside conscious control, and outside whatever is happening in your relationship or your head. If they are still occurring, the machinery works, which points the investigation towards psychological and situational causes rather than vascular or hormonal ones.
If they have disappeared, that is the finding worth taking seriously, and it is one of the three symptoms the European study identified.
How this should be assessed
Properly, the question is not "is my testosterone low". It is "which of the several possible causes is operating in me, and in what proportion".
That means the three symptoms taken seriously as a group rather than one in isolation. It means cardiovascular risk assessed rather than assumed. It means every medication reviewed. And it means the hormone measured correctly, in the morning, confirmed, with LH and FSH alongside it.
Done in that order, the answer is usually clear. Done backwards, starting with the hormone, a lot of men end up treated for the wrong thing while the real cause carries on unexamined.
Which symptoms belong together is covered in the signs men actually notice. What the vascular side means for the rest of you is in low testosterone and your heart.
Wu FCW, et al. "Identification of Late-Onset Hypogonadism in Middle-Aged and Elderly Men." New England Journal of Medicine, 2010. doi:10.1056/NEJMoa0911101