Axial spondyloarthritis (axSpA) is a chronic inflammatory disorder that primarily affects the axial skeleton, including the spine and sacroiliac joints.1 It encompasses both nonradiographic axSpA (nr-axSpA) and radiographic axSpA (also known as ankylosing spondylitis [AS]), the latter characterized by radiographic evidence of sacroiliitis.2 AxSpA significantly affects the quality of life and physical functioning of affected individuals. Although the pathogenesis of axSpA is not fully understood, a combination of genetic, immunologic, and environmental factors contributes to its development. In recent years, obesity has emerged as an important factor influencing axSpA disease course and outcomes.

The global prevalence of obesity is staggering, with over 1 billion individuals affected, including 650 million adults, 340 million adolescents, and 39 million children.3 Further, this number continues to rise, and it is estimated by the World Health Organization that by 2025, approximately 167 million people, encompassing both adults and children, will experience compromised health due to overweight or obesity.3

Excessive weight gain and obesity are characterized by an abnormal accumulation of fat that can have detrimental effects on health.4 To classify overweight and obesity in adults, body mass index (BMI) is commonly used as a simple index of weight in relation to height. BMI is calculated by dividing a person’s weight in kilograms by the square of their height in meters (kg/m2). BMI was created as a practical and quantifiable estimate of body fat percentage. The National Institutes of Health has divided BMI into 3 categories for classification purposes: a BMI below 25 kg/m2 signifies a normal-weight status, a BMI between 25 and 30 kg/m2 indicates overweight, and a BMI exceeding 30 kg/m2 denotes obesity.5 In recent years, BMI in rheumatic diseases has received increased attention in research and literature and is seen as an important element in assessing the overall health and disease management of individuals with axSpA. A recent study from the Ankylosing Spondylitis Registry of Ireland examined the prevalence of central obesity in axSpA. Both BMI and waist:hip ratio (WHR) were used to compare classifications of obesity.6 The analysis included a total of 753 patients, among whom 29.6% (n = 223) were identified as obese based on BMI, whereas 41.3% (n = 311) were categorized as centrally obese using the WHR. The authors concluded that using WHR assessment should be used in conjunction to BMI to identify central obesity in patients with axSpA that may be missed using BMI measurement alone, which should allow for timely intervention and improved patient outcomes.6

Overall, the prevalence of obesity in different inflammatory rheumatic diseases is generally similar to or slightly higher than that observed in the general population.7 In patients with axSpA, it remains a frequently encountered comorbidity that seems to be more common than in the general population, with a reported prevalence of 14% to 27%.8-10 Notably, the prevalence of obesity in axSpA appears to be influenced by factors such as sex, sociodemographic status, and age across populations.6,10,11

The presence of excess fat in adipose tissues triggers the release of inflammatory mediators such as tumor necrosis factor and interleukins,12 promoting a proinflammatory state within the body.13 Obesity has been shown to be associated with increased disease activity,6,10,14,15 radiographic progression,16 and functional impairment in patients with axSpA.15 In addition to obese individuals with axSpA experiencing worse outcomes, including increased pain and reduced spinal mobility, obesity can significantly affect the response to treatment in patients with axSpA. Evidence suggests obesity may affect the efficacy of biologic agents such as tumor necrosis factor inhibitors (TNFi), which are used for the management of axSpA. Higher adiposity levels have been associated with lower drug levels, decreased clinical response, and an increased risk of treatment discontinuation.17-19 It is worth noting, however, that a study looking at patients with AS based on the biologic drug database in Turkey (TURKBIO) registry between 2018 and 2021, which suggested that obesity did not affect secukinumab treatment response and drug retention,20 with similar results in studies in psoriatic patients.21

Given the substantial effect of obesity on axSpA outcomes, it is crucial to address obesity as part of the management strategy. Comprehensive management of axSpA should include a multidisciplinary approach involving rheumatologists, physiotherapists, and nutritionists. Lifestyle interventions focusing on weight loss, physical activity, and healthy eating habits should be implemented. Additionally, tailored treatment strategies considering the effect of obesity on medication response and potential drug interactions are warranted.

In this issue of The Journal of Rheumatology, Micheroli et al highlight how obesity represents a persisting health issue in axSpA, particularly affecting socially disadvantaged patients.22 The economic burden associated with obesity, including healthcare expenses and reduced productivity, disproportionately affects individuals from lower socioeconomic backgrounds.23 Individuals in disadvantaged socioeconomic circumstances often face numerous obstacles that contribute to the development and perpetuation of obesity. Limited education regarding food choices and availability of affordable and nutritious food options creates barriers to maintaining a healthy diet. The effect of obesity in lower socioeconomic settings is multidimensional, with adverse health outcomes including an elevated risk of chronic diseases such as diabetes, cardiovascular disorders, and certain cancers.22 Addressing obesity in these settings requires comprehensive strategies that focus on structural, environmental, and individual factors aiming to improve access to healthy foods, promote physical activity, and provide education and support for healthy lifestyle choices.

The findings of this study by Micheroli et al in a Swiss cohort of patients with axSpA and obesity hold significant importance for both medical practice and public health interventions.22 The study provides valuable insights into the association between axSpA and obesity, demonstrating that patients with axSpA have a higher prevalence of obesity compared to the general population. This sheds light on the potential role of obesity in disease initiation and progression, as well as the need to address this risk factor. Identifying obesity as a prevalent risk factor in patients with axSpA opens up possibilities for risk reduction and disease prevention. Healthcare providers can focus on proactive measures to manage obesity, potentially mitigating the risk of developing axSpA or reducing disease activity in patients with existing axSpA. Recognizing that obesity is more common among patients with axSpA, despite Switzerland’s relatively low obesity rates, emphasizes the necessity for targeted public health interventions.22 These initiatives could include awareness campaigns, lifestyle interventions, and resources to promote weight management and physical activity.

Finally, Micheroli et al again highlight that obese patients with axSpA tend to experience higher disease activity, showing higher rates of arthritis, heel enthesitis, and elevated C-reactive protein levels compared to normal-weight patients.22 The rate of definite radiographic changes in the sacroiliac joints was also higher in obese patients, indicating more advanced disease progression. This highlights the importance of addressing obesity not only for its general health implications but also for its potential effect on disease severity and management.

Although this study provides valuable data, it also highlights the need for more extensive research to fully understand the relationship between obesity and axSpA. Further studies could explore causality, biomarkers, and the effect of weight reduction on disease outcomes in patients with axSpA. It also suggests that drug interventions for weight reduction could be beneficial for obese patients with axSpA who may have limitations in physical exercise due to elevated disease activity. This opens up avenues for exploring new therapeutic options in managing axSpA more effectively.

In conclusion, obesity represents a prevalent issue within the axSpA population. The higher prevalence of obesity in patients with axSpA compared to the general population underscores the need for healthcare providers to consider the impact of obesity on disease progression and treatment outcomes. Addressing obesity through comprehensive management strategies can play a crucial role in optimizing outcomes and improving the overall well-being of individuals with axSpA.

The authors declare no conflicts of interest relevant to this article.

See Obesity in axSpA, page 1587