Why men wake up with erections

TheConversation: The morning penile erection, or as it is medically known, “nocturnal penile tumescence”, is not only an interesting physiological phenomenon, it can also tell us a lot about a patient’s sexual function. Morning penile erections affect all males, even males in the womb and male children. It also has a female counterpart in the less frequently discussed nocturnal clitoral erection.

What causes erections?

Penile erections occur in response to complex effects of the nervous system and endocrine system (the glands that secrete hormones into our system) on the blood vessels of the penis.
When sexually aroused, a message starts in the brain, sending chemical messages to the nerves that supply the blood vessels of the penis, allowing blood to flow into the penis. The blood is trapped in the muscles of the penis, which makes the penis expand, resulting in an erection.
Several hormones are involved in influencing the brain’s response, such as testosterone (the main male hormone).
This same mechanism can occur without the involvement of the brain, in an uncontrolled reflex action that is in the spinal cord. This explains why people with spinal cord damage can still get erections and why you can get erections when not sexually aroused.

What about erections while we sleep?

Nocturnal penile erections occur during Rapid Eye Movement (REM) sleep (the phase during which we dream). They occur when certain areas of the brain are activated. This includes areas in the brain responsible for stimulating the parasympathetic nerves (“rest and digest” nerves), suppressing the sympathetic nerves (“flight and fight” nerves) and dampening areas producing serotonin (the mood hormone).
Sleep is made up of several cycles of REM and non-REM (deep) sleep. During REM sleep, there is a shift in the dominant system that’s activated. We move from sympathetic (fight and flight) stimulation to parasympathetic (rest and digest) stimulation. This is not found during other parts of the sleep cycle.
This shift in balance drives the parasympathetic nerve response that results in the erection. This is spontaneous and does not require being awake. Some men may experience nocturnal penile tumescence during non-REM sleep as well, particularly older men. The reason for this is unclear.
The reason men wake up with an erection may be related to the fact we often wake up coming out of REM sleep.
Testosterone, which is at its highest level in the morning, has also been shown to enhance the frequency of nocturnal erections. Interestingly, testosterone has not been found to greatly impact visual erotic stimuli or fantasy-induced erections. These are predominantly driven by the “reward system” of the brain which secretes dopamine.

Since there are several sleep cycles per night, men can have as many as five erections per night and these can last up to 20 or 30 minutes. But this is very dependent on sleep quality and so they may not occur daily. The number and quality of erections declines gradually with age but they are often present well beyond “retirement age” - attesting to the sexual well-being of older men.
It’s also important to highlight the counterpart phenomenon in women, which is much less researched. Pulses of blood flow in the vagina during REM sleep. The clitoris engorges and vaginal sensitivity increases along with vaginal fluidity.

What’s its purpose?

It has been suggested “pitching a tent” may be a mechanism for alerting men of their full overnight bladder, as it often disappears after emptying the bladder in the morning.
It’s more likely the reason for the morning erection is that the unconscious sensation of the full bladder stimulates nerves that go to the spine and these respond directly by generating an erection (a spinal reflex). This may explain why the erection goes away after emptying one’s bladder.
Scientific studies are undecided as to whether morning erections contribute to penile health. Increased oxygen in the penis at night may be beneficial for the health of the muscle tissues that make up the penis.

What does it mean if you don’t get one?

Loss of nocturnal erection can be a useful marker of common diseases affecting erectile function. One example is in diabetics where the lack of morning erections may be associated with erectile dysfunction due to poor nerve or blood supply to the penis. In this case, there’s a poor response to the messages sent from the brain during sleep which generate nocturnal erections.
It is thought nocturnal erections can be used as a marker of an anatomical ability to get an erection (a sign that the essential body bits are working), as it was thought to be independent of psychological factors that affect erections while awake. Studies have suggested, however, that mental health disorders such as severe depression can affect nocturnal erections. Thus its absence is not necessarily a marker of disease or low testosterone levels.
The frequency of morning erections and erection quality has also been shown to increase slightly in men taking medications for erectile dysfunction such as Viagra.

So is all this morning action good news?

While some men will put their nocturnal erections to good use, many men are not aroused when they have them and tummy sleepers might find them a nuisance.
Since good heart health is associated with an ability to have erections, the presence of nocturnal erections is generally accepted to be good news. Maintaining a healthy lifestyle is important in avoiding and even reversing erectile dysfunction, so it’s important to remember to eat healthily, maintain a healthy weight, exercise and avoid smoking and alcohol.