ED is caused by vascular, hormonal, neurogenic, pharmacological, or psycho-genic factors. Performance anxiety where the person fears failing in a sexual scenario is a common psychogenic cause for ED.3 Neurogenic causes are related to diseases like Alzheimer's, Parkinson's, stroke or spinal cord injuries. Radical removal of the prostate (also called prostatectomy) is the cause of nerve-related ED as nerve injury is possible despite advances in surgical methods.4

For example, you’ll often hear that watermelon is a great remedy for ED.  This belief seems to come from a study done in 20075, which showed that consuming watermelon could raised levels of L-arginine in the bloodstream.  L-arginine is used in the production of nitric oxide (NO), which is a key to healthy erections (see our article, “How Do Erections Work“).  However, the study did not show that consuming watermelon actually improved erections.  Also, the subjects consumed the equivalent of three eight-ounce glasses of watermelon juice per day!
If you bike a lot and have a very narrow saddle on your bicycle, consider switching to a "no-nose seat" which is wider at the back than a conventional saddle, allowing more of your weight to be distributed to the sitting bones. Make sure the seat is level or angled slightly downward and at a height that allows your knee to be just slightly bent at the bottom of the pedal cycle. Raising the handlebars on your bike so that you're sitting upright may also help.
Other factors that “stress” the body can also increase your risk for ED. These include: substance abuse, using marijuana, smoking cigarettes, depression, anxiety and low self esteem. Cigarette smoking — or using nicotine — leads to constricted blood vessels, which has negative effects for sexual health. Other mental/emotional obstacles can cause less desire for sex and decrease testosterone. Several ways to help manage stress include:
Poor sleep patterns can be a contributing factor for erectile dysfunction, Mucher says. One review published in the journal Brain Research emphasized the intricate relationship between the level of sex hormones like testosterone, sexual function, and sleep, noting that testosterone levels increase with improved sleep, and lower levels are associated with sexual dysfunction. Hormone secretion is controlled by the body’s internal clock, and sleep patterns likely help the body determine when to release certain hormones. 
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