Please provide information regarding the effect of running on penile
function.  Specifically, could running three to five miles a day
without wearing any athletic support contribute to, if not cause,
erectile dysfunction?

Dear efuseler,

While there are several accepted causes of erectile dysfunction (ED),
including medical conditions (illness, hormone imbalances, especially
Diabetes), emotional/relationship issues and certain medicines, I
couldn't find any information linking running/jogging without an
athletic supporter with ED.

Running without an athletic supporter may lead to minor injuries
(depending on one's stride and speed and the size of one's
penis/testicles, general fitness, et cetera) that shouldn't have a
lasting effect because when they happen, the person immediately stops
the activity to deal with the discomfort and/or pain involved. If
someone is running 3-5 miles a day for a long period of time without
experiencing any pain, running would not likely be the cause of ED.

Athletic supporters mostly provide safety from contact injuries
(bruising and rupture) when worn with a cup, and discomfort otherwise.
"Some advertisemnents refer to preventing strain on the scrotum and
spermatic cord, but these may be overrated. European soccer players
seem to get along fine without athletic supporters." from:
http://www.infernosoft.com/community/hockey/jock/jockstraps/

It also notes that athletic supporters do not prevent hernias (related
to strain on the scrotum and spermatic cord). Although you didn't ask,
there was no evidence found supporting a connection between a hernia
and erectile dysfunction, though logic would indicate what if there is
an injury, obtaining an erection may be painful or impossible until
the injury has healed.

If this is your situation, you should talk to a urologist or your
family doctor about the situation, as there may be some underlying
cause that can be corrected with treatment or should be under medical
supervision. In these situations, the sooner the better. This answer
does not constitute medical advice, per the Google disclaimer below.

--------------
- REFERENCES -
--------------

General Information on Impotence/ED:

General: http://familydoctor.org/handouts/466.html
Specific: http://www.merck.com/pubs/mmanual/section17/chapter220/220a.htm
List of links: http://www.alt-support-impotence.org/info_frame.htm

Information on Athletic Supporters:
http://www.infernosoft.com/community/hockey/jock/jockstraps/

----------------------------
- SUPPORTING DOCUMENTATION -
----------------------------

Soccer 411
http://www.soccer-411.com/Soccer_Camps.html

European Soccer Equipment Rules:
http://www.fifa2.com/scripts/runisa.dll?S7:gp::67173+refs/laws (pdf
files, English version, page 15 (8th thumbnail) contains the list, no
athletic supporters needed)

------------------------------------
- Google Search Terms and Strategy -
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penile dysfunction contraindications running
cause erectile dysfunction
safety reasons wear "athletic supporter"
strain scrotum spermatic cord
erectile dysfunction hernia
cause hernia 
inguinal hernia 
soccer european rules safety (to verify European Soccer players don't
have to wear supporters)

While I was very impressed with the response made to the question, I
think I know where the person who asked it is coming from in this
matter.  From personal experience I have found that when I run great
distances with no support of any kind, my sexual desire decreases
dramatically.  If I refrain from running for a few weeks to "heal", I
find I am back to my normal self again.  My observations lead me to
believe that there is some small trauma done to the insides of the
testicles from all the bouncing.  Certainly this would be dependent on
many factors--temperature, for example, which would cause the scrotum
to either sag or contract, either giving more natural support or less.
 During this time, for me personally, I can force myself to achieve an
erection, and I can masturbate or have sex successfully.  However, my
body is not directing me as it norally does to do these things.  I do
not wake up with morning wood, in other words, and a twice a day
masturbation habit might cut down to every two or three days.  For me,
it is simple cause and effect.  This person may very well have an
excellent point, although studies and data collection would be
necessary to prove it.  I think the solution is obvious--that he wear
an athletic supporter while jogging.