Association Between Physical Activity and Joint Symptoms Modified by BMI in Middle-Aged Women

Data collected over the course of a dozen years revealed that low-level physical activity (PA) is required to protect the joints of middle-aged women.¹ This protective effect was most prominent in obese women, indicating a modifying effect of body mass index (BMI) on PA affecting joint symptoms’ incidence and prevalence. There was no relationship found between menopausal or hormone therapy (HT) status and this protection.

Researchers used survey responses from the Australian Longitudinal Study on Women’s Health, collected every 3 years between 1998 and 2010, to assess joint pain and stiffness in relation to PA levels, HT and menopausal statuses, and BMI. Previous studies indicated complex associations between PA and osteoarthritis (OA)², prompting investigators to examine potential modifiers to further elucidate possible protective or damaging influences of PA on OA symptoms. Their approach accounted for PA behavioral fluctuations over time, something other studies had not examined.

 

A total of 6661 participants (mean age, 49.5 years; standard deviation, 1.5 years) were evaluated in this prospective cohort study. As opposed to those either meeting or nearly meeting guidelines, those who reported PA levels of “none or low” or “fluctuating” also reported much higher prevalence of joint symptoms (36.6% and 32.2% of each group, respectively, vs 19.9% and 21.2% for meeting or nearly meeting guidelines, respectively) at the conclusion of the study.

After adjusting for modifiers and confounders, the authors found that those in the “none or low” group (odds ratio [OR], 1.60; 99% CI, 1.08-2.35, P =.002) and the “fluctuating” group (OR, 1.34; 99% CI, 1.04-1.72; P =.003) had much higher odds of joint symptom incidence over time. However, BMI stratification revealed that only overweight (OR, 1.49; 99% CI, 1.22-1.84; P <.001) or obese (OR, 2.26, 99% CI, 1.78-2.86; P <.001) women experienced a statistically significant effect of PA level on joint symptom incidence and prevalence.

Higher PA levels in larger women appeared to have a protective effect on joint pain and stiffness. As the researchers stated, “This finding is particularly of importance as it counters the concern that [PA] may increase the risk of joint symptoms in obese people due to joint loading.”

Neither HT nor menopause appeared to significantly alter the effect of PA on joints, with the exception of those receiving long-term HT (significant incidence) and those in the “non/short-term” group (significant prevalence). In addition, women who had undergone oophorectomy and/or hysterectomy had increased risk for joint symptom incidence and prevalence.

 

Study strengths included large sample size and using repeated measurements over time, allowing for pattern detection. In contrast, a major weakness lies in self-reporting, making findings less objective. Also, although the goal was evaluation of PA on OA joint symptoms, it is likely that some reports were the result of nonarthritic pain.

The results clearly reveal that at least a low level of PA is beneficial and protective against joint symptoms in middle age, with the most pronounced effect seen in those with higher BMIs.

The investigators are hopeful that these results can offer etiological clarity and help clinicians guide their patients in the use of preventive behaviors and interventions aimed at reducing joint pain and stiffness among middle-aged women.

Reference

1. Peeters G, Edwards KL, Brown WJ, et al. Potential effect modifiers of the association between physical activity patterns and joint symptoms in middle aged women [published online December 6, 2017]. Arthritis Care Res. doi:10.1002/acr.23430
2. Lee R, Kean WF. Obesity and knee osteoarthritis. Inflammopharmacology. 2012;20(2):53-58.