I would love to see real statistics on this as I am sure it is significantly higher.
In Hobart congregation sickness was a fashion. If the fashion was Candida everyone had it, next it was Chronic Fatigue, then allegies. Depression is probably the latest. One elder with an overbearing wife spent the last 20 years in bed with heart problems, and listened to the meeting by phone hookup, along with about 20 other people that were too sick to attend meetings. Managed to stay an elder somehow. His wife is very old and sick now and I have heard he is out and about now and got his vigour back now his wife is unable to control him any longer.
I have heard figures that 80% of illness can be related to stress, so it indicates to me JWs are stressed by the pressure of their beliefs, definitely not a case of "take my yoke for it is lowly and light"