Feeling sad? Sit in Lotus. Better yet, rise up into a backbend or soar royally into King Dancer Pose. While it’s not as simple as that, one study found that a consistent yoga practice improved depression and led to a significant increase in serotonin levels and a decrease in the levels of monoamine oxidase (an enzyme that breaks down neurotransmitters) and cortisol. At the University of Wisconsin, Richard Davidson, Ph.D., found that the left prefrontal cortex showed heightened activity in meditators, a finding that has been correlated with greater levels of happiness and better immune function. More dramatic left-sided activation was found in dedicated, long-term practitioners.

Move more, eat less—that's the adage of many a dieter. Yoga can help on both fronts. A regular practice gets you moving and burns calories, and the spiritual and emotional dimensions of your practice may encourage you to address any eating and weight problems on a deeper level. Yoga may also inspire you to become a more conscious eater.

An important component of yoga is focusing on the present. Studies have found that regular yoga practice improves coordination, reaction time, memory, and even IQ scores. People who practice Transcendental Meditation demonstrate the ability to solve problems and acquire and recall information better—probably because they’re less distracted by their thoughts, which can play over and over like an endless tape loop.