Many people are oxygen-deprived because they do not breathe deeply. Try to live in a place where the air quality is good. Many big cities have notoriously poor air quality. Consider a home air purifier if you live in a particularly bad area. Ten minutes of sunlight per day, even if only on exposed arms, is enough to encourage normal vitamin D production.
Sunlight has mood-elevating effects.
It destroys harmful bacteria and stimulates a cascade of positive hormone effects in the body. While excessive sun exposure can be harmful, so can inadequate exposure. Outdoor exercise will give the necessary sunlight without excess. Make it a point to get a modest amount of sunlight per day, whether by outdoor exercise or ten minutes of sunbathing. The human body is designed for movement.