3 Answers

Many. Just a sample:

Lack of hygiene, unhealthy lifestyle, insufficient nutrition, intoxication (long term or short term), drug abuse, lack of exercise, exposure to radioactivity, massive exposure to ultraviolet rays, adverse climate, lack of sleep, genetic particularities, emotional/psychological stress, ignorance, ... 

and so on and so forth  

I believe decease has been pass on from generation before us and living in filthy and unsanitary,and uneducated life,more like animals.but time have change and we got better in prepare our food,and clean water,However we have now contaminate our genes with all kind of poisons,take pain killer to reduce our suffering only making matter worst.Now some of us are over educate bumb.

There are many, many.  Papitou has mentioned some of them.  For me, the main casue of my chronic disease is work.  I used to say, "I am sick of work!"