The key is to go outside, get some natural light and sun on your skin. Most of us reading this are vitamin D deficient year after year.
Covid has had an advantage on anyone lacking proper vitamin levels.
That's at least 10 hours of sleep per day, for a large part of the year.
It's also no sleep at all, in some parts of the year, for some countries.
So 9am and 5pm respectfully for me I guess.
That being said the key to it all for a relatively healthy person is mental and physical fatigue and lack of stress.
On the other hand... my wife used to live near loading-unloading train station and worked at 2 jobs for some time. Takes her 10 minutes to fall asleep regardless.
Try doing the same in New York, to say nothing of places like Stockholm.
Getting outside a bit is a great advice most everywhere, though. It's not always going to produce a lot of vitamin D, when you wear clothes mostly covering your skin, but it has other advantages.
At winter time it get really dark really fast and usually there is only sunlight for a couple of hours per day.