Populations living at a latitude higher than 37° north of the equator in the Northern Hemisphere are at the greatest risk of developing vitamin D deficiency.
It's typically not sound itself that wakes us up or keeps us from falling asleep in the first place. Rather, it's the harsh changes in sound that wake us up -- think a slamming door, a barking dog, a crack of lightning. That's where sleep sounds come in. -The secret to better sleep: Pink, blue and brown noise - CNET