My colleague is pointing to some stats that could be helpful, so I'm going to quickly go to this page.
I have some statistics here. After retirement, if we ask people why they retired, the issue of health comes first again. Illness and disability were the most reported reasons provided by older workers ages 55 to 64; 17.2% tell us they had to retire due to health reasons. For seniors 65-plus, 9.3% say they left a job because they could not do their job. This is from a 2011 survey.
If we look at older adults ages 55 to 64, not in the workforce but who would like to work, 30% told us in 2011 that they did not look for work because they were sick. It was for a health reason. You would have to add that 30% of those who did not even look for work because they were sick to those who had to leave their jobs because they were sick. This is quite substantial.