Introduction Insight in the impact of within-individual changes in working conditions, health behaviour and body mass index (BMI) on work ability and self-rated health is essential to develop effective policies aimed at prolongation of working lives.

Objectives This study assessed the impact of 1) within-individual improvements, and 2) within-individual deteriorations in working conditions, health behaviour and BMI on changes in work ability and self-rated health among workers.

Methods The Dutch Study on Transitions in Employment, Ability and Motivation (STREAM) was used to identify participants whose working conditions, health behaviour, and BMI improved (N=14,045) or deteriorated (N=14,066) at least once during seven year follow-up (2010–2017). The impact of within-individual improvements and deteriorations in health behaviour (moderate- and vigorous physical activity, smoking status), BMI, psychosocial (psychological- and emotional job demands, autonomy, social support) and physical working conditions in a given year on changes in work ability (0–10 scale) and self-rated health (1–5 scale) in the same year were analysed with fixed-effects regression models.

Results Workers with deteriorated physical or psychosocial working conditions decreased in work ability (β’s: -0.21 (95%CI: -0.25;-0.18) to -0.28 (95%CI: -0.33;-0.24)) and health (β’s: -0.07 (95%CI: -0.09;-0.06) to -0.10 (95%CI: -0.12;-0.08)), whereas improvements in working conditions were to a lesser extent associated with increased work ability (β’s: 0.06 (95%CI: 0.02;0.09) to 0.11 (95%CI: 0.06;0.16)) and health (β’s: 0.02 (95%CI: 0.00;0.03) to 0.04 (95%CI: 0.02;0.06)). Workers with increased BMI or decreased physical activity had reduced work ability and health. Likewise, decreased BMI or increased vigorous physical activity was associated with improved health. An increase in moderate or vigorous physical activity was modestly associated with a reduced work ability. Quitting smoking was associated with reduced work ability and health.

Conclusion Preventing deteriorations in working conditions, health behaviour and BMI could be of importance for sustainable employability.