Obesity Drives Increased Arthritis Rates in Younger Adults

Janis C. Kelly

March 15, 2017

The Centers for Disease Control and Prevention (CDC) recently published data showing that one in four Americans suffers from arthritis. Now, data from a major Canadian longitudinal study suggest that even those prevalence estimates might be too low.

In addition, the data show that arthritis prevalence is rising among younger cohorts, report Elizabeth Badley, DPhil, Professor Emeritus, from the Dalla Lana School of Public Health at the University of Toronto, Ontario, Canada, and colleagues.

They suggest that obesity is driving the increase among younger cohorts. "Projections which only take into account the changing age structure of the population may underestimate future trends. Our understanding of the impact of BMI [body mass index] on arthritis is likely an underestimate," Dr Badley and colleagues write.

Dr Badley​ told Medscape Medical News, "The CDC projections are based on an increasing proportion of the population who are older and therefore at risk for arthritis and other chronic diseases — and are grounded in the age and sex specific distribution of these chronic diseases taking into account the obesity as it is now. If the proportion of obese people (overall or differentially by age and sex) in the population changes then this could affect projections for chronic diseases that are associated with obesity (such as arthritis, diabetes heart disease) — either up or down.​" 

Four Cohorts Studied

In the study, published online March 8 in Arthritis Care & Research, Dr Badley and colleagues analyzed longitudinal data for 8817 subjects from the Canadian National Population Health Survey 1994-2011.

They studied four cohorts including persons born during World War II (born 1935-1944), older baby boomers (born 1945-1954), younger baby boomers (born 1955-1964), and Generation Xers (born 1965-1974). Unlike with other population-based studies that use repeated cross-sectional data collection, Dr Bradley and colleagues were able to follow the same individuals over time.

As expected, the team found that arthritis prevalence increased with age.

However, they also found that individuals in each successive cohort were more likely to report arthritis than those in older cohorts at the same ages. Modeling the effect of risk factors on the age-cohort model showed that only BMI and smoking were statistically significant.

"The odds of reporting arthritis increased with increasing levels of BMI," the authors write. "For example, those who were in the severe obese category were 2.5 times more likely to report arthritis than those of normal weight. Furthermore, non-smokers (OR: 0.57, 95% CI: 0.51; 0.66) were less likely to report arthritis than current smokers."

The authors note that arthritis age trajectories were shifted by obesity. Cohort differences were greater for obese individuals than for normal-weight individuals, and their age trajectories were steeper, suggesting that obese individuals developed arthritis years earlier than normal-weight individuals in the same birth cohort.

"In every cohort it seems that the benefits of societal changes in increasing income, education and smoking cessation on potentially reducing the prevalence of arthritis, have been largely off-set by the effect of increasing obesity over time," the authors comment.

"In other words, had it not been for the increasing prevalence of obesity over time, the prevalence of arthritis might have declined in all cohorts, with the corollary that our understanding of the impact of BMI on arthritis prevalence trends is likely to be an underestimate." They warn that current projections of arthritis prevalence based only on the age structure of the population may be too low for obese individuals.

The clinical implications of this analysis affect both the design of arthritis education programs and the care of obese patients. The authors explain, "The cohort differences also focus attention on the need to target arthritis management and education to young and middle-aged adults. Not only was the cohort effect of higher arthritis prevalence more marked in those who were obese compared to those of normal weight, in all cohorts the age of onset of arthritis in obese individuals was earlier."

This study was funded in part by a CIHR Operating Grant–Secondary Analysis of Databases (SEC 117113). The Statistics Canada Research Data Centres (RDC) Program provided access to the data file.

The authors disclosed no relevant financial relationships.

Arthritis Care Res (Hoboken). Published online March 8, 2017. Full text

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