Remember, green plants purify the air and give us back more oxygen. Houseplants help purify indoor air. Practice deep breathing exercises. 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.