Prolonged repetitive manual work that includes lifting heavy objects or bending increases the risk of developing rheumatoid arthritis, a new study has found.
Although work-related physical activity over many years is known to cause many cases of osteoarthritis (OA) in selected joints, this is the first study to show a link between physical workload and rheumatoid arthritis (RA).
To examine whether physical workload is a possible risk factor for RA, information on different types of self-reported exposure was analysed from a population of 3,680 RA patients and 5,935 matched controls.
To study whether some people are more susceptible than others, the risk was compared in subjects with and without a specific genotype (HLA-DRB1), and an analysis was performed in relation to the presence/absence of ACPA (anti-citrullinated protein antibodies) among RA patients.
"We found that some types of physical workload increased the odds of developing RA more than others," said Pingling Zeng from the Karolinska Institute in Sweden.
"There also appeared to be a significant interaction between genetic makeup, in terms of HLA-DRB1 genes, and the risk of ACPA-positive RA from specific types of physical workload," Zeng said.
The estimated odds ratio of developing RA in exposed vs unexposed subjects was greater than or equal to 1.5, with several repetitive types of manual work that would be common, for example, in the building trade: exposure to repeated vibration (1.5), carrying or lifting weights greater than 10kg (1.5), bending/turning (1.6), and working with hands either below knee level (1.7), or above shoulder level (1.8).