Erectile dysfunction (ED) may affect a third of all men, including up to a quarter of men under 40 (estimates vary widely because of differences in the definition of ED), and the number of men with ED globally could reach 332 million by 2025. Although we think of ED as a sexual health issue, there is strong evidence that it is a flashing warning light for several other conditions, including insulin resistance, heart disease, dementia, and vascular disease. ED is more common in older men, but it’s not necessarily an inevitable consequence of aging; instead, it’s linked to other conditions, like diabetes or cardiovascular problems.
The connection between ED and glucose control is not surprising: We’ve known that men with diabetes are two to three times more likely to develop ED. But ED may appear even before a diabetes diagnosis. A study of men who had been recently diagnosed with ED found that more than 20% had undiagnosed prediabetes. If you develop ED under 45, it’s a good idea to have your doctor screen for early signs of elevated glucose and insulin resistance.
So how does high blood sugar become a sexual health problem? An erection is a complex physiological process, but it ultimately centers around vascular function: To oversimplify, the arteries relax and blood flows in; at the same time, veins close and effectively trap the blood. There are several places along that vascular cascade of actions that things can go wrong, and it turns out poor glucose control and insulin resistance play a role in many of those dysfunctions.
ED as a Metabolic Warning Sign
The link between metabolic disease and ED bears out in several studies around the world. One of the few longitudinal studies of nearly 1,500 men with Type 2 diabetes found that one-third of them had “frequent erectile problems” at the beginning of the study, and another 13% developed ED over the three years of the research. The men who developed ED during the study tended to be older, to have worse metabolic control, or to have had diabetes for a longer time.
Most studies in this space are cross-sectional, meaning that they look at a group of men at one point in time to tease out associations, rather than causation. One study in the U.S. showed that men with diabetes were more likely to have ED. Another research project, conducted in Italy, found that 19% of men with ED had impaired fasting glucose (IFG), and almost 22% had diabetes. The men with IFG were also more likely to have severe ED than the men with normal fasting blood glucose levels. Another study found that the more severe the metabolic disease, the worse the ED (as indicated by a commonly-used diagnostic questionnaire).
How Glucose Influences ED
To see how high glucose levels and insulin resistance connect to ED, it helps to understand the basic physiology of an erection, which involves a synchronized set of vascular, hormonal, neurological, and psychological mechanisms.
Sexual arousal sets off excitatory signals in the brain. This, in turn, causes the release of nitric oxide (NO) and acetylcholine, which act on the penile arteries, inducing them to relax and fill with blood, which leads to an erection. NO specifically is a crucial player, interacting with a protein called endothelin 1 to cause blood vessels to dilate or constrict.
ED is ultimately a vascular (blood vessel) malfunction—a well-known feature of insulin resistance or impaired glucose control—that can be caused by disruption of NO. Several different pathways can act on NO levels, and all have a relationship with metabolic dysfunction.
Testosterone is one hormone that can stimulate NO production in endothelial cells, the cells that make up the lining of blood vessels. Low testosterone can lower NO levels in the endothelial cells of the penis, which can ultimately lead to ED. Research suggests that insulin resistance is associated with reduced testosterone production by the testicles’ Leydig cells. Another review found that low testosterone is a risk factor for developing metabolic syndrome. Testosterone may also affect how the body takes in and uses glucose.
Testosterone treatment has been shown to improve insulin resistance in people with diabetes who suffer from hypogonadism (low testosterone). But studies on using testosterone to address ED in patients with diabetes have shown small effects. Still, given the relationship between testosterone, metabolic syndrome, and ED, some experts recommend people with ED check both glucose and testosterone levels.
High glucose levels may disrupt vascular function through substances called advanced glycation end products (AGEs), which form when glucose reacts with proteins or fats and sticks to them. AGEs are more abundant when blood glucose levels are high. They reduce NO levels and can cause micro- and macro-vascular abnormalities in diabetes. One study showed that people with diabetes displayed higher AGE levels in the penile tissue, which could reduce NO in the endothelium of the penis, resulting in ED
- Neurological dysfunction
High glucose levels can also disrupt erectile function by interfering with the normal working of the nerves in the penis. In an erection, these nerves are activated and use nitric oxide synthase (NOS) to produce NO, which then stimulates increased blood flow to the penis. However, high blood glucose seems to disrupt NOS production in endothelial cells, which creates conditions that reduce NOS and NO in the nerves (one factor in a well-known condition called diabetic or prediabetic neuropathy), and can lead to ED.
ED as an Indicator of Cardiovascular Risk
Since metabolic disease and heart disease are closely linked, it makes sense that ED is also strongly associated with heart disease. So much so that ED increased the risk of heart disease 1.5 to 2.6 times (compared with men without ED), about the same increase in risk associated with well-established factors such as smoking, high fat levels, or having a family member with heart disease. Strikingly, having ED increased the risk of heart disease in younger men (under 60) more than in older men. One also found that the more severe the ED, the higher likelihood of developing heart disease.
ED can also be an earlier warning sign of vascular disease than heart disease or diabetes. Problems in vasodilation in the arteries of the penis lead to less blood flowing through the penile arteries. Since the penile arteries are smaller in diameter than the arteries in the heart, for example, the reduced blood flow may cause ED before any problems show up elsewhere. Also, penile arteries are end arteries, meaning that they cannot branch out further to form subsidiary arteries, which could otherwise compensate somewhat for the reduced blood flow.
What Can You Do About It?
If you have ED or even ED risk factors, talk to your doctor about checking your blood sugar and cholesterol levels. If the results are high, your doctor may recommend changes to your diet and exercise, and perhaps medications as well. By taking steps to address risk factors such as high blood glucose, you could help prevent or delay nerve and blood vessel damage that can cause ED. It could also help prevent diabetes and heart disease and improve your overall health.