The vertebrae in the neck are fragile. Although Sirsasana (Headstand) can be beneficial, you need to approach it with caution—preferably with an experienced teacher who can guide you to prevent injury. Women who are in any stage of osteoporosis can be especially vulnerable to injury in Headstand if they don't perform it correctly or don't have the necessary muscular strength.
If you aren't steady on your way into or out of Headstand, consider working toward it in stages. Your instructor can help assess your ability and guide you until you're ready to do it on your own. For additional instruction, take a look at Anatomy of Hatha Yoga by H. David Coulter (Body and Breath, 2001).
Have someone spot you until you can move into, hold, and come out of the pose with control. If you're misaligned or your weight is poorly distributed, you'll not only have an imperfect Headstand, you'll also put excess strain on your upper body or overcompress or overstretch the vertebrae, ligaments, tendons, and muscles in the neck, which can lead to serious injury.
Keep your neck in alignment and distribute your weight evenly between your head, elbows, and forearms to prevent yourself from falling. Place your weight on the crown of the head. To ensure a solid foundation, grasp opposite elbows on the floor to measure the distance apart before bringing your hands forward and together. Once you're up in Headstand, focus on one point in front of you, breathe, keep your head centered, and don't turn your face to either side.
Tony Sanchez is founder of the U.S. Yoga Association, established in 1984 to teach the health and fitness benefits of hatha yoga.