Abstract
OBJECTIVE: In two randomized controlled trials, the Plants for Joints (PFJ) multidisciplinary lifestyle intervention reduced signs and symptoms of rheumatoid arthritis (RA), or metabolic syndrome-associated hip or knee osteoarthritis (MSOA) compared with usual care. This secondary analysis aimed to evaluate the effect of the PFJ intervention on stress-related parameters. METHODS: In two PFJ observer-blind randomized controlled trials (RCT), people with (1) RA with low-moderate disease activity or (2) MSOA were randomized to receive the PFJ lifestyle intervention or usual care. The 16-week PFJ intervention consisted of a whole-food plant-based diet, physical activity, and sleep and stress management. This secondary analysis investigated stress-related outcomes including heart rate, heart rate variability (HRV: root square mean of successive differences (RMSSD) and normalised high frequency (HFnorm), salivary cortisol, perceived stress (Perceived Stress Scale 10; PSS-10), and time spent on stress-reducing activities. An intention-to-treat analysis with a linear regression model (HRV) or linear mixed model (cortisol and PSS-10), adjusted for baseline values, was used to analyse between-group differences. RESULTS: 77 people with RA and 64 with MSOA completed the RCT. RA participants following the PFJ intervention showed a significant improvement in HFnorm (between-group difference: 6.6; 95 % CI 0.5, 12.6) and an improving trend in RMSSD (4.3; 95 % CI -1.5, 10.1) alongside non-significant reductions of heart rate (3.1; 95 % CI-3.9, 10.1), salivary cortisol (1.3; 95 % CI -0.6, 3.1) and perceived stress (-2.0; 95 % CI -4.4, 0.3), compared to usual care. In participants with MSOA, there were no differences in heart rate, HRV outcomes, cortisol, or perceived stress between the intervention and control group. Both RA and MSOA participants temporarily increased time spent on stress-reducing activities, yet no change from baseline was observed after 16 weeks. In RA participants increased time spent on stress-reducing activities was associated with increased HFnorm. CONCLUSION: This secondary analysis suggests the PFJ program may have a positive influence on stress-related parameters in people with RA, but not MSOA, compared to usual care.