I'm more inclined to believe that the 8 hours of sleep recommended has no basis on science; but as I said above, this study has many flaws. First of all the study subjects averaged 67.6 years of age. That makes the study hardly applicable for all the people on this forum. Second, they were all women, so it does not apply to men either. The data is adjusted which essentially mean they are not reporting what the investigators observed. And part of the data came from sleep questionnaires. That alone makes it very dubious since it relies on the memory of the subjects which extremely frequently fails. So don't take it so seriously. Apparently the studies on sleep are pointing to less sleep to be better; but those kind of studies are usually unreliable.