Sunglasses prevent the critical natural UV light from the sun which is required for optimal body functions hormones mental health, circadian rhythm etc.

Learned about this through the work of Dr Jack Kruse and others:

“Proper UV light signaling to the brain helps synchronize hormonal release, optimize energy production, and protect mitochondrial health. Disruption of this light input—such as from chronic indoor living or artificial lighting—can impair mitochondrial efficiency and contribute to fatigue, mood disorders, and metabolic dysfunction.”