Color me completely unsurprised. Sleep deprivation has already been linked to heart disease, obesity and early stage Type 2 diabetes, due to its undermining functions like metabolic control. I would have been more surprised if it didn't affected our mental health.
Unfortunately, not only do we get a lot less sleep than evolution intended due to electric lights, but many of us (myself included) prioritize sleep after many other items on our to-do lists. Even if you get enough hours of sleep, any disruption can still undermine your efforts. A good night's sleep includes several cycles consisting of one REM (Rapid Eye Movement) stage and four non-REM stages. REM sleep has long been considered the most important stage, but each stage addresses a different brain function, so you need several complete cycles to maintain a healthy brain. So if your child, for instance, wakes up in the middle of the night and has to be put back to bed, you've already disrupted one of the cycles, even if you're only awake for five minutes.
I think it's possible that sleep deprivation has something to do with the fact that I've had depression since childhood. I have always been a very heavy sleeper, even as a child. In fact, I wet the bed to a relatively late age because of it, and I was an occasional sleepwalker. Until a couple of years ago, I assumed that this meant that I slept well. But I found out by doing some research that it apparently can mean that you sleep poorly, and consequently are so sleep deprived that it's hard for you to wake up because of a full bladder or other factors.
As a related aside, I've seen evidence recently that lack of sleep can change a child's personality. Overall, my five year old son is fairly easy-going, not aggressive and rarely hyper. Until I started working full-time in June, he went to bed at a relatively early hour and got at least ten or eleven hours sleep. Once I started coming home at 5:30, he was going to bed later and getting less than ten hours of sleep. After about two months of the later bedtime, his personality changed so much that he was getting daily time-outs at school due to shoving other children and calling them names (he also did some of this at home). In addition, despite having virtually no accidents since he was toilet trained, he started having frequent accidents at both home and school. Once I figured out what the problem was and got him to bed earlier, his personality went back to normal.
It seems likely that a healthy amount of sleep is essential for your mental as well as physical well-being. If the quality and/or amount of sleep you get is less than optimal, there are some things you can use to improve it. The first thing to do is to talk to your doctor. You may be suffering from an undiagnosed medical condition that is interfering with your sleep. If no obvious cause is found, there are a couple of things you can try on your own.