Mortality statistics show that UC causes a reduction of only about
a few months in the average lifespan of an individual. We are talking days here, not years. So on average you might miss out on a few months aged 76.2! I'm not gonna worry about
Note that this is what happens on average. A small amount of people may develop a serious condition, others may even live longer than the national average. But on average the reduction in longevity due to UC is pretty small and will continue to get smaller with advances in medicine.
CD causes a larger reduction in longevity but still relatively small. I forget the stat quoted. I think it's something in the region of 1 year below the national average lifespan.
If you want more on this check out the World Health Organisations database. They have numbers and stats on almost ever disease known to man!