There are four categories of ED causes

DEAR DR. ROACH >> A friend has been suffering from persistent erectile dysfunction, whereby he can achieve (usually) an erection but has difficulty maintaining it. He is currently in rehab for a lower-back injury, so it could be physical rather than psychological in nature.

He has sworn to me that he is going to talk to his doctor. In the meantime, he doesn’t believe in the effectiveness of any home remedies he has researched. Can you help?

— P.L.H.

DEAR READER >> In general, there are four systems whose problems can lead to erectile dysfunction: blood flow, hormones, nerve supply and psychological. They work together closely, so that any one of them can cause problems in one of the others, which makes finding a single cause problematic.

Before trying therapy, his doctor ought to at least consider problems in all of these areas, especially blood flow, since occasionally erectile dysfunction is the presenting symptom of blockages in the arteries. Most docs also will take a look for hormone problems, especially testosterone and prolactin. Given his back injury, nerve problems are more likely in him than in others, although ED seldom is the presenting symptom of neurological disease.

Psychological factors, especially partner issues, are a dramatically underrecognized cause of ED. Once when I gently suggested the possibility to a patient, he replied that if I weren’t a doctor, he would hit me in the face for making the suggestion. I took that as evidence tending to confirm my hypothesis. Medications can be problematic, and his back problem may have him taking opiates, which can cause ED. Alcohol, thiazide diuretics and beta blockers often are causes.

Medications like sildenafil (Viagra) are effective for ED from any of these causes in many or most cases; however, the patient and clinician need to be aware that ED could be a first sign of disturbance in the four systems I mentioned.

DEAR DR. ROACH >> It seems like there has been an increased effort to make sports safer and prevent concussions. However, I do not hear about an increased effort to prevent head injuries in car accidents. It seems that this is an even more universal issue than sports injuries, since most people drive, but not all people play sports. Also, has there been research about the long-term effects of repeated concussions in car accidents over a lifetime, or does medical research think that because the concus- sions are spread over time, the body is able to heal?

— C.G.

DEAR READER >> The issue in contact sports is that repeated head trauma may lead to chronic traumatic encephalopathy. In the case of motor vehicle accidents, few people should have enough repetition to develop this complication, and modern seat belts and air bags greatly reduce trauma to the head and brain.

DEAR DR. ROACH >> In a recent column, you imply that taking folic acid in the presence of B-12 deficiency could be a problem. Please clarify this and explain exactly what you mean. I usually have a borderline B-12, and I take folic acid daily. Am I causing harm to myself?

— P.A.M.

DEAR READER >> In people with an undiagnosed B-12 deficiency who also have low folic acid, taking a folic acid supplement can cause the production of red blood cells to accelerate, which further depletes the B-12 stores. Very low vitamin B-12 can cause serologic and psychiatric complications, and many physicians check B-12 levels before starting on folic acid. If B-12 is low, supplementation of B-12 before starting folic acid should prevent this complication.