What are the causes of erectile dysfunction?

Many things: This problem can only be solved by seeing your doctor and being evaluated face-to-face. After a thorough examination, your doctor should be able to tell you what's wrong and what to do about it.

Not likely . . .: Erectile dysfunction is not so much a result of vitamin deficiency as it is stress (whether due to relationship, partner, family, friends, money, job, etc), poor lifestyle choices (smoking, drinking to excess, etc) & bad health (high blood pressure & cholesterol + diabetes, etc) plus medications used to treat said conditions. Good nutrition & regular exercise are key to regaining health.

Many reasons: There are many factors that can cause erectile dysfunction. A urologist can help you figure out if something medical is going on. Feeling stressed, anxious, or conflicted in a relationship can also be some possible reasons. Of course it could be a combination of several things. I would recommend getting things checked out medically first. Then consider seeing a therapist.