A combination of bladder pressure as well as testosterone levels contribute. Men have several nocturnal erections every night and it's one way of determining impotence caused by medical issues from the psychological. This is entirely normal. The time to worry is when nocturnal and morning erections no longer occurr.
The involuntary nocturnal erections are nature's way of keeping all of the vascular systems in peak running condition. if you do not have them you risk penile atrophy and fibrosis issues (which can be a problem for those of us who have had prostatectomies and for others with illnesses that might cause vascular problems). So don't discourage them .. ENcourage them by checking your patner frequently at night. o if you are having trouble and NOT getting them you can ask your doc for daily Cialis (5mg) or other ED meds.
It's because of the full bladder which puts pressure on whatever and causes the erection. Get up to pee at 4am and go back to bed and you will not wake up with morning wood.
With all due respect, this is incorrect. As the other posters have said, early AM erections are natures way of protecting the vascular system in the penis as T levels are at their highest early in the morning. The absence of early AM erections is almost always correlated to low T and / or ED. As "Just tell me" said, the time to worry is when they don't occur, not when they do.
My husband does not always get them , he is in mid 40's, but IF I touch him, the erection grows, so I am not too worried about it. He does have low -but normal levels of Testosterone as he was tested last year. He is not eligable for Test treatment.
I am wondering if -having sex daily, acheiving these full erections is JUST as good as getting a morning erection -for vascular health? We do have sex 4-6 times a week, but it is a rare thing for him to wake up with an erection these days. He even told me in his youth, he did not always get these morning erections. But it never failed if he would indulge in sexual thoughts in his youth. Then he was 100% erect. But not waking up that way.