Why the penis is a barometer of men's health - and we need to wake up to its warnings - BBC

Erectile dysfunction can be an early warning of a heart attack, stroke, diabetes and dementia. It's time that patients and doctors alike started taking notice, according to researchers.

You could describe erectile dysfunction as a silent epidemic. According to multiple surveys, it afflicts more than half of adult men over 40. Few, however, are willing to discuss the issue with the people they love.

If the topic does come up in conversation, it's often seen as the subject of banter – rather than an early warning sign of impending illness. Yet, according to reams of new research, the penis is often a barometer of a man's overall health, with erectile dysfunction acting as a harbinger of many serious conditions, including diabetes, heart attack, stroke and dementia.

It is a "canary in the coalmine", according to sexologist Emmanuele Jannini at the University of Rome Tor Vergata, who recently edited a scholarly book reviewing the evidence to date. With better screening for erectile dysfunction, doctors could therefore diagnose some serious threats to men's health before they have progressed too far.

But many men's reluctance to talk about their sexual health means that they are missing these valuable opportunities.

Here's what you need to know about this extremely common complaint and the reasons it should ring alarm bells for your doctor.

Like many medical conditions, the precise prevalence of erectile dysfunction depends on how you define and measure it. As a result, studies report its global prevalence among adult men spanning from just 3% to 76.5% – a huge range. But one of the largest and most nuanced surveys examined around 1200 subjects using detailed questionnaires and found that 39% of men aged 40 regularly experienced some level of impotence, rising to 67% at age 70.

In many ways, erectile dysfunction is a plumbing problem.

Along the length of the penis run two spongy structures called the corpora cavernosa, which are typically flaccid. When a man becomes aroused, the brain sends signals to relax the muscles around the penis's arteries, creating an influx of blood into both of those cylinders. As they expand, the corpora cavernosa start stretching, and they compress the veins ushering blood outside the penis, trapping it inside.

Like a balloon filling with air, the organ expands and stiffens. Anything that reduces the build-up of blood through the penis's pipes will impair a man's capacity to achieve or maintain that erection.

The issue is often psychological. A stress response involving adrenaline and cortisol can lead our blood vessels to contract, preventing the corpora cavernosa from stiffening. Heightened levels of stress can also interfere with the production of testosterone, which can reduce libido and dampen arousal. (Importantly, people with glandular conditions like hypogonadism also have reduced production of testosterone, so this can play a role.)

That's not to mention that stress often comes with a general state of mental distraction that may make it hard to stay focused on sex.

There would have been a good reason for this in our evolution: if stress halts arousal, it ensures the body preserves its resources for survival in moments of danger. "If the environment is risky, it's important not to reproduce," says Jannini.

In the modern world, however, there are many non-life-threatening reasons we experience stress, so this protective mechanism might be called into action more often than necessary.

In many cases, erectile dysfunction may also reflect far broader health problems. For one, it can arise from atherosclerosis – a condition in which blood vessels harden and narrow, leading to a major risk of heart disease. Since the penis's arteries are among the smallest in the body, they are often the first to fail, so cases of erectile dysfunction can act as a harbinger for this type of heart failure.

Analysing data from 154,794 individuals, one recent paper found that men with erectile dysfunction were 59% more likely to suffer coronary heart disease, and 34% more likely to have a stroke.

"A good measure of vascular health is having a good erection," says Michael Carroll, an expert in reproductive science at Manchester Metropolitan University in the UK, and author of the forthcoming book Your Nuts: The Science of How They Work and What It Means For Your Fertility, which is set for publication this summer.