Here is the science:

Sirsasana stimulates and provides refreshed blood to the pituitary and hypothalamus glands. These glands are vital to our wellbeing, and are considered the master glands that regulate all other glands in the body (thyroid, pineal, and adrenals).

Sirsasana increases digestive fire and increases body heat. The intestines are cleansed by reversing the pull of gravity, while releasing congested blood in the colon.

Improved circulation occurs with a regular Sirsasana practice.