Yoga is a science that has been practiced for thousands of years. It is consists of Ancient Theories, observations and principles about the mind and body connection which is now being proven by modern medicine. Substantial research has been conducted to look at the Health Benefits of Yoga - from the Yoga Postures (Asanas), Yoga Breathing (Pranayama), and Meditation. The information on Yoga Poses & Benefits are grouped into three categories-physiological, psychological, biochemical effects. Furthermore, scientists have laid these results against the benefits of regular exercise.

Physiological Benefits of Yoga

Stable autonomic nervous system equilibrium
Pulse rate decreases
Respiratory rate decreases
Blood Pressure decreases (of special significance for hyporeactors)
Galvanic Skin Response (GSR) increases
EEG - alpha waves increase (theta, delta, and beta waves also increase during various stages of meditation) ...more

Source: http://www.abc-of-yoga.com/beginnersguide/yogabenefits.asp

A lot of people have questioned how yoga and their own spiritual beliefs can come together. Yoga actually pre-dates religion.

Blood Pressure decreases

Probbaly one has to make some experiments on EEG with Yoga to support its benefit.