Some forms of abnormal kyphosis can be prevented. Postural kyphosis, for example, is entirely dependent on posture, so if you maintain good posture, you will prevent this type of kyphosis from developing. To develop good posture, you need to be aware of how you're standing or sitting. Read the article Posture and Kyphosis for tips on how to have good posture.
Kyphosis caused by osteoporosis and spinal fractures is also preventable. You need to keep your bones strong and healthy to avoid osteoporosis. By doing things such as eating foods rich in calcium and other vital nutrients, you will be doing your body—and bones—good. There are many other things you can do to prevent osteoporosis; it's one of the most preventable diseases. Osteoporosis Prevention is full of more tips on how to have healthy bones.
You can't prevent Scheuermann's kyphosis or congenital kyphosis because they're caused by structural defects that develop no matter what you do. However, with Scheuermann's kyphosis, the earlier you catch it, the better. If you notice that your pre-teenager or teenager has poor posture, make an appointment with your doctor. He or she will be able to determine if it's postural kyphosis—which is correctable by re-learning good posture—or it it's Scheuermann's kyphosis.
If you catch structural kyphosis early enough and follow your doctor's treatment plan, you may be able to prevent the abnormal kyphosis from having an extreme effect on your spine.