Age-related degenerative changes in the spine like lumbar spondylosis, bone spurs, and herniated disks are the most common causes of sciatica. 
Excess body weight can exert more pressure and strain on the spine, due to which you may develop spinal changes responsible for triggering sciatica.
People whose job requires them to twist their back, drive motor vehicles for long periods, and carry heavy loads are more vulnerable to develop sciatica. These activities cause more strain on the muscles in the back due to which their ability to withstand pressure or strain is reduced. This puts the person at a risk of developing nerve compression or the herniation of the disc while lifting heavy weights or during a heavy bout of cough.
People who live a sedentary lifestyle and have to sit for prolonged periods are more likely to develop sciatica as compared to the people who are physically active.
Diabetes can increase the chances of nerve damage due to which the risk of sciatica may increase substantially. 
What are the complications of sciatica?
- Loss of sensation in the affected leg
- Severe weakness or paralysis of the affected leg
- Loss of bowel and bladder functions
Ignoring the early warning signs of sciatica can lead to progressive nerve damage. Moreover, the pain and discomfort caused due to sciatica can interfere with your routine activities. It can prevent you from performing your daily activities efficiently and even deprive you of the things you love to do such as gardening, playing sports, cycling, swimming, and so on. This marks the importance of seeking timely medicinal intervention to relieve pain and prevent nerve damage.
- B W Koes, professor, M W van Tulder, professor of health technology assessment, and W C Peul, neurosurgeon, Diagnosis and treatment of sciatica, 2007 June, 334(7607): 1313–1317, doi: 10.1136/bmj.39223.428495.BE, PMCID: PMC1895638,PMID: 17585160
- D W Zochodne, C Cheng, H Sun, Diabetes increases sciatic nerve susceptibility to endothelin-induced ischemia, 1996 May, 45(5):627-32. doi: 10.2337/diab.45.5.627, PMID: 8621014