Obesity is a risk factor for worse overall health in people with ankylosing spondylitis (AS), and is associated with increased inflammation, disease activity, and cardiovascular risk, a Taiwanese study has found.
Therefore, preventing obesity in these patients is important to help improve their disease outcomes, researchers said.
The study, “Association of obesity with inflammation, disease severity and cardiovascular risk factors among patients with ankylosing spondylitis,” was published in the International Journal of Rheumatic diseases.
Obesity increases the risk for many disorders, such as diabetes and cardiovascular diseases. However, how obesity impacts AS severity has been rarely studied.
Researchers in Taiwan assessed the link between obesity and clinical manifestations in AS by evaluating total obesity using body mass index (BMI) and central obesity using waist circumference (WC) and waist-to-height (WHtR) ratio — two well-established measures of cardiovascular disease risk.
Patients were considered overweight if their BMI score was 24 kg/m2 to 27 kg/m2, and obese when BMI was 27 or greater. A WC measure of at least 80 centimeters (cm) for women and 90 cm for men was used to define central obesity. A WHtR of 0.5 or higher was the cut-off value for central obesity.
In total, the researchers evaluated 105 AS patients (92 men and 13 women, median age 48 years). According to BMI scores, 40 patients were considered normal weight, 36 overweight, and 29 obese. Sixty-seven patients were considered centrally obese, according to their WC, and 77 according to the WHtR.
A total of 11 patients (10.5%) had diabetes, and 19 patients (18.1%) had hypertension, or high blood pressure.
The scientists observed significantly higher levels of C-reactive protein (CRP) — a marker of inflammation — in the obese group across the different measures analyzed.
Disease activity, measured by the Ankylosing Spondylitis Disease Activity Score (ASDAS)-CRP, was also higher in obese patients across BMI, WC, and WHtR. For instance, patients who were not obese, according to BMI, had an ASDAS-CRP score of 1.91 vs 2.581 in the obese group.
The team also assessed physical mobility, using the Bath Ankylosing Spondylitis Metrology Index (BASMI), and damage to the spine and hip joints using the Bath Ankylosing Spondylitis Radiology Index and the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS), a four-point radiographic scoring system.
Across all three indices (BMI, WC, and WHtR), obese participants had significantly higher (meaning worse) scores in BASMI and m-SASSS than non-obese patients. Liver function, assessed by the levels of alanine aminotransferase, was also worse in the obese.
Taken together, these findings indicate that obese AS patients had worse mobility and higher spinal joint damage.
Higher CRP levels correlated with greater scores across the three obesity indices, while greater disease activity (ASDAS-CRP) correlated with WC and WHtR, but not with BMI. This suggests a weak positive correlation between inflammation and disease activity in AS patients, the researchers said.
Further analyses showed that obese AS patients, according to BMI, had significantly worse overall health status than non-obese participants, as shown by the Taiwanese version of the SpondyloArthritis International Society Health Index (ASAS-HI). The ASAS-HI ranges from 0 to 17, with lower scores indicating better health.
Blood pressure also correlated with all three indices, with the risk of hypertension increasing with obesity.
WHtR was the best parameter to predict high CRP levels, disease activity, physical mobility, and spine damage, as well as overall health status.
Also, all three obesity indices could predict risk of diabetes among AS patients, and WC and WHtR were significant predictors of hypertension.
A smaller analysis of 39 patients monitored for spine changes on X-rays showed that WC and WHtR were significantly associated with differences in m-SASSS, after adjusting for sex, spine change duration, and CRP.
Overall, these results show that “obesity was associated with higher inflammation, disease activity, physical mobility, radiographic damage, health index, liver function and cardiovascular risk factors in AS,” the researchers wrote. “Central obesity is a better predictor for high disease severity, and may participate in the inflammatory process of AS.”
As such, strategies to prevent obesity are important to improve patient outcomes, the team said, adding that larger and longer studies are needed to fully understand the association between obesity and AS.
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