there should definitely be more research done in this area. i know that hormone levels are affected by insulin balances, and since insulin is often affected in adult cf'ers, i have to think that there is some link.
of course, the simple answer is energy, perhaps even body chemistry, we are on drugs all the time, and those drugs have indirect effects on all of our body processes, it would be unreasonable to assume that sexual function is not at all affected. particularly drugs that affect the circulatory system, blood pressure, etc. low body salinity can affect blood pressure, which can in turn affect ability to achieve or maintain erection. many bronchodilators (albuterol, atrovent) have an effect on heart rate, which can also have an effect on wood. also, megace, a commonly prescribed, cf drug, is going to affect hormone levels, particularly in men. then there are the various ingredients in herbal and vitamin supplements, and a host of interactions thereof.
for me, personally, the meds have made it difficult to achieve orgasm, therefore many sexcapades turn into marathons, which my body 29 year-old body can't always keep up with. i have to really, really want it, or be hyper-turned on in order for sex to completed even within the normal half hour span. over the years, i think i have developed an aversion to sex because of this. cf cocktails only exacerbate this. i still like sex, but it is becoming an ever increasing source of frustration, continuing the spiral.
bottom line - sex is a psycho-chemical body process. anything that effects the psyche, or body chemistry (which is pretty much everything) is going to affect sexual response/functioning. being as cf care affects both, the situation is ripe for adverse sexual functioning.