I found this to be a humourous article…
http://www.straightdope.com/classics/a3_221.html
Does saltpeter suppress male ardor?
16-Jun-1989
Dear Cecil:
As a lad I went to the same repressive boarding school that made George Bush what he is today. As a student I believed, as did we all, that the school authorities were mixing potassium nitrate, or saltpeter, into our food to control our sexual appetites. (The food itself controlled our regular appetites.) Is this true? Was it legal? Would it have had any lasting effect on me? I shudder to think what happened to poor George. –John Daniel, Santa Barbara, California
Dear John:
The official word is that potassium nitrate (KNO3), more commonly employed as an ingredient in gunpowder, has no therapeutic value as an anaphrodisiac, contrary to legend. Cecil of course believes this. Still, when you look at what the stuff does do, you can see where the idea got started. Saltpeter can cause relaxation of involuntary muscle fiber (for which reason it’s used to treat asthma) and it’s occasionally prescribed to lower body temperature in cases of fever. From there it’s not much of a leap to think that “niter,” as it was called in the old days, might cure “sexual fever,” and in fact a few doctors urged it for that purpose centuries ago.
From what I can tell the idea wasn’t taken too seriously, but apparently sailors in the British navy leapt to conclusions when they learned that potassium nitrate was being used to preserve the meat used aboard their ships. Ever since the inmates of almost any large all-male institution, ranging from boarding schools to the army, have been convinced that the higher-ups were slipping the stuff into the mashed potatoes (or whatever) to cool the jets of the rank and file. During the world wars, for example, it was widely believed that government-issue cigarettes were soaked in saltpeter.
The truth is that even the most tyrannical general wouldn’t inflict the stuff on his men if he expected them to be of any use–too many side effects. Among other things potassium nitrate can cause gastroenteritis (violent stomachache), high blood pressure, anemia, kidney disease, and general weakness and torpor. It also has an alarmingly depressive effect on the heart. Too strong a dose and not only would you not be able to get it up, chances are you wouldn’t be able to get up, period. All in all, there’s still no substitute for the cold shower.
–CECIL ADAMS