Another completely logical and more reasonable assumption is that healthier people tend to be wealthier.
Well... sometimes the medical expenses can ruin you financially. I know once incident (one of my close friends) where the insurance company rejected a claim for Kidney transplant. It cost him around $300,000. He wasn't that wealthy, and his entire savings were blown away. Now he is in deep debt. Feeling bad for him.... as he is just 36 y.o.