It's also true that as the body ages, the discs slowly dry out. This process affects the disc strength. The discs don't bounce back under pressure like they used to. Poor posture along with incorrect body mechanics stresses the lumbar spine. All these factors affect its normal ability to carry the bulk of the body's weight. An extra 50, 100, or more pounds increases the stress or load even more.
Now add daily wear and tear, injury, incorrect lifting, or twisting and the risk of disc herniation increases. For example, lifting something incorrectly can cause disc pressure to rise to several hundred pounds per square inch!
To summarize, risk factors include poor posture and poor body mechanics. Weak abdominal muscles, smoking, and obesity can also increase risk. Start now to change your habits and help your body preserve the discs for many years to come.
Lars Ekström, BS, et al. In Vivo Porcine Intradiscal Pressure as a Function of External Loading. In Journal of Spinal Disorders. August 2004. Vol. 17. No. 4. Pp. 312-316.