Aviation has some inherent risks, more than just flying close to the speed of sound.
when you fly you are exposed to Cosmic, Solar and Electromagnetic radiation.
The body can tolerate some limited amounts of radiation but increased Altitude, Latitude and Duration can impose high amounts of cosmic radiation. Some airlines monitor this to limit exposure.
Flying is not a Monday to Friday 9 to 5 job. its akin to shift work. working irregular schedules and and night shift. you loose sleep, working over night of hopping time zones. This can have negative health consequences. Get lots of Sleep
Working in an enclosed space with lots of people will often expose crews to lots of virus' and bacteria. so take your vitamin C.
If you get sick, book off, no one wants to work with someone who't sick and it spreads. If you have plugged ears, you set yourself up for major damage to your ears with pressurization changes over the flight.
Alcohol, while a little red wine might be good for the arteries, too much isn't good for the liver. In Canada it's 8 hours bottle to Throttle but in reality, its more like 12 to be safe. It's not worth your job.
If you need help there are AA groups and one called Birds of a Feather for aviators.
HIV, its a different world now and its not a death sentence. Transport Canada isn't so much concerned about the virus but the medications. It does need to be volunteered to your Canadian Aviation Medical Examiner. They are pretty good about it.
Anytime you start a new medication, you shouldn't fly in case you have any reactions.
Whenever you see your doctor, advise them if you are a pilot.
Sex Changes, It's been done before, so if you have sex reassignment you can get your documents changed to the new gender and Transport Canada will help you get your license back after surgery. Again, it's the drugs they worry about.