Sunlight exposure, specifically ultraviolet light, stimulates nitric oxide production in the skin, which is essential for blood vessel health and dilation.

“well Sun on your skin makes nitric oxide”

“how about nitric oxide that's made in your skin in response to the ultraviolet light from the sun that is essential for the health of your blood vessels and their dilatation”

“release of nitric oxide in the skin cells induced by moderate exposure to UVA in sunlight may be especially beneficial for some demographic groups such as the elderly hypertensive patients or those with impaired nitric oxide function not only during exposure but many hours and days after that”

“release of nitric oxide in the skin cells induced by moderate exposure to UVA in sunlight may be especially beneficial for some demographic groups such as the elderly hypertensive patients or those with impaired nitric oxide function not only during exposure but many hours and days after that”