There are interesting challenges with data collection (and I don't think the survey paper discussed in the OP really solves this problem), but to be clear, somewhere between 10-30% of Americans average fewer than 6 hours of sleep per night, which increases your risk of catching colds by 450%.
So getting less sleep than you need is definitely harmful, the questions become: a) how much do we really need, b) how much are people actually getting, and the jury still seems to be out on both of these.
So getting less sleep than you need is definitely harmful, the questions become: a) how much do we really need, b) how much are people actually getting, and the jury still seems to be out on both of these.