Risk factors for low back pain with special reference to current smoking

I greatly appreciate the study by Parreira et al., a systematic review on risk factors for low back pain (LBP) or sciatica [1]. The authors conducted an umbrella review and the following adverse risk factors were specified: older age, smoking habit, physical stress on spine by vibration and depression. I have a query with this study with special reference to smoking.
Source: The Spine Journal - Category: Orthopaedics Authors: Tags: Letters to the editor Source Type: research