# Exercise as it relates to Disease/Obesity and the rise in the incidence of Rheumatoid Arthritis

This is a critique of the research article: Cynthia S. Crowson, Eric L. Matteson, John M. Davis III, and Sherine E. Gabriel for 'The Contribution of Obesity to the Rise in Incidence of Rheumatoid Arthritis': An inception cohort study. Arthritis Care & Research. American College of Rheumatology. Vol.65, No.1, January 2012, pp. 71–77.
The critique was written as an assignment in the unit: Health, Disease and Exercise at University of Canberra, September 2019.

## Background to this research

Rheumatoid Arthritis (RA) is an autoimmune disease where the body's immune system attacks the tissue around joints and other parts of the body, mainly affecting small joints such as the hands and feet but can also be seen to affect the hip and knee joints. About 458,000 Australians (1.9% of the total population) are affected, while 41 out of every 100,000 people in the US are diagnosed with RA every year.
Obesity is thought to be an under recognised risk factor of RA. Obesity and RA prevalence have both been on the rise, therefore it is thought that there may be a relationship between the two diseases. These diseases exhibit similar characteristics as both involve high inflammation in the body, obesity involves inflammation of adipose tissue while RA involves chronic systemic inflammation. Further research and a growing understanding of Adipokines have explained their important role as negotiators of inflammation and immune response, which are also involved in the pathophysiology of rheumatic diseases, in which RA is one.
The aim of this study was to assess the influence of obesity on the risk of developing RA, and to determine whether obesity could explain the increasing incidence of RA.

## Where is the research from?

This study was conducted and completed by four authors; Cynthia S. Crowson, Eric L. Matteson, John M. Davis III and Sherine E. Gabriel. All of which were involved in the writing of the article or revising intellectual content. All authors have previously and since been involved in multiple research and scholar articles. The authors own claims correspond with the results and were all appropriate to this research topic. Therefore, we can assume that they are reliable sources.
The research was completed by the American College of Rheumatology in 2012, a professional organisation based on improving the care/understanding of rheumatic disease and improving the rheumatology subspecialty.

## What kind of research was this/ What did the research involve?

This was an inception cohort, retrospective, population-based study. The study was conducted using resources of the Rochester Epidemiology Project.
Conditional logistic regression was used to assess the influence of Obesity on developing RA. Population attributable risk was used to estimate the incidence of RA in the absence of obesity.
Participants included:
* 813 residents of Olmsted County, Minnesota.
* Aged ≥18 years.
* Who fulfilled the 1987 American College of Rheumatology criteria for RA in 1980-2007.
* They were compared to population-based controls (Matched on age, sex and calendar year).
* The mean age of both groups was 55.9 years.
* 68% were women.
* Obesity was defined as a BMI ≥30 kg/m².
The method for this study was appropriately chosen. The Rochester Epidemiology Project (REP) is a collaboration of medical facilities in Minnesota and Wisconsin, and allows for shared medical records for research. REP has been a reliable information source for hundreds of research articles, not just the article in this critique. However the size of the Olmsted County population creates a limitation as REP only accounts for 502,820 individuals (As of 2012), the small population that would then meet the needs of this particular study may affect the reliability of the results, a bigger study would be more accurate. A cohort study is also an appropriate choice as it allows the researchers to look at groups of people, possible risks and disease in relation to them.
This study has been supported by a number of reliable references, the study results can also be supported by a number of other scholar articles/research studies in the same field. A report conducted by Jennifer M. Hootman et al. found "Arthritis is common among U.S. adults with obesity (35.6%)". Another study conducted by Lynda F. Voigt et al. found "Women in the highest quartile of body mass index had a risk of 1.4 (95% CI = 1.0-2.0) relative to women with lowest body mass index" in terms of being diagnosed with RA. Bing Lu et al. also found "Risks of seropositive and seronegative RA were elevated among overweight and obese women, particularly among women diagnosed with RA at earlier ages".

## Results:

A history of obesity was somewhat more common in cases than in controls (40% verses 36%, P=0.052), whereas obesity at the incidence/index date was similar in cases and controls (30% versus 28%, P=0.41).
The cases had a higher BMI at the incidence/index date on average (mean 28.2 versus 27.2 kg/m², P=0.004), with 95% of cases and 85% of controls categorised as over-weight at the incidence/index date.
Conditional logistic regression models revealed that history of obesity was a significant risk factor for the development of RA (OR 1.24, 95% confidence interval (CI), P=0.046), whereas obesity at the incidence/index date did not reach statistical significance (OR 1.10, 95% CI).
Association between obesity and developing RA was similar for both sexes.
Table 2. Prevalence of obesity in patients with and without RA according to sex, age, and calendar year of the index date* (1) :
| RA: | 1980-1989 | 1990-1999 | 2000-2007 |
| Female: 18-39yrs: 40-59yrs: ≥60yrs: | 8/15 19/33 13/37 | 12/24 34/41 23/33 | 32/38 54/62 35/46 |
| Male: 18-39yrs: 40-59yrs: ≥60yrs: | 22/22 32//32 17/31 | 10/10 32/38 36/48 | 23/46 40/42 33/51 |
| Non-RA: | | | |
| Female: 18-39yrs: 40-59yrs: ≥60yrs: | 19/27 19/21 10/22 | 24/32 33/39 16/38 | 24/24 46/54 44/46 |
| Male: 18-39yrs: 40-59yrs: ≥60yrs: | 11/11 15/25 14/26 | 0/10 20/20 27/33 | 42/42 35/40 49/65 |
*Values are the percentage of patients with obesity at the index date/percentage of patients with history of obesity prior to the index date.Association between history of obesity and development of RA was somewhat stronger among patients aged <60 years at the incidence/index date (OR 1.32, 95% CI versus OR 1.15, CI 95%).
However, results also show that obesity could explain 52% of the increase in the incidence of RA among women from1995-2007. Sensitivity analyses were performed, the estimated OR being 1.24 (95% CI 1.01-1.53). If the relative risk (RR) for obesity on the development of RA was only 1.01, then only 18% of the increase in RA incidence could be explained, while if the RR was as large as 1.50, 82% could be explained among women.

## Conclusions

The conclusions that can be drawn from this article is that a moderate risk for developing RA is associated with obesity, especially among women.These findings suggest that unless the obesity epidemic is controlled, prevalence of RA will continue to rise. With this rise also comes the demands for increased funding and rheumatologic care.
More research would need to be completed to further confirm these findings. This study was published in 2012, since then there has been an even greater rise in the prevalence of obesity and RA. This studies results may now be out of date/irrelevant, a similar updated study with a greater population would be suggested. Although the study was conducted with appropriate methods, and results did show a relationship between obesity and RA, the percentages were low in areas and the relationship between the two diseases was not confirmed for men. In conclusion this study was very well organised, with great sources of information and qualified authors. The results confirmed the hypothesis for certain population groups, however the age of the study and the small amount of participants affects the reliability of the results.

## Practical advice

To avoid the risk of Obesity and Rheumatoid Arthritis:
* Maintain physical activity guidelines: 150–300 minutes of moderate intensity, or 75–150 minutes of vigorous activity.
* Eat a healthy balanced diet.
* Avoid/Quit smoking.
* Be consistent in your healthy lifestyle, create a healthy routine and GET HELP EARLY!!
* More on RA.
* More on obesity.

## Further readings/insights

For further information/interesting readings, follow the links below:
* Evolving concepts of Rheumatoid Arthritis.
* Obesity in rheumatoid arthritis
* Association of obesity with worse disease severity in rheumatoid arthritis as well as comorbidities.
* Obesity and inflammation.

## References

* 1 2 3 4 5 Crowson C, Matteson E, Davis J, Gabriel S. Contribution of obesity to the rise in incidence of rheumatoid arthritis. Arthritis Care & Research. 2012;65(1):71-77.
* ↑ Rheumatoid arthritis, Impact of rheumatoid arthritis - Australian Institute of Health and Welfare [Internet]. Australian Institute of Health and Welfare. Available from: https://www.aihw.gov.au/reports/chronic-musculoskeletal-conditions/rheumatoid-arthritis/contents/who-gets-rheumatoid-arthritis
* ↑ Rheumatoid Arthritis by the Numbers: Facts, Statistics, and You [Internet]. Healthline. Available from: https://www.healthline.com/health/rheumatoid-arthritis/facts-statistics-infographic#1
* ↑ Wood I, Trayhurn P. Signalling role of adipose tissue: adipokines and inflammation in obesity. Biochemical Society Transactions. 2005;33(5):1078.
* ↑ American College of Rheumatology [Internet]. Rheumatology.org. Available from: https://www.rheumatology.org
* 1 2 St Sauver J, Grossardt B, Yawn B, Melton L, Pankratz J, Brue S et al. Data Resource Profile: The Rochester Epidemiology Project (REP) medical records-linkage system. International Journal of Epidemiology. 2012;41(6):1614-1624.
* ↑ In the News | Rochester Epidemiology Project [Internet]. Rochesterproject.org. Available from: https://rochesterproject.org/in-the-news/
* ↑ MacGill M, Timothy J. Legg C. Cohort study: Finding causes, examples, and limitations [Internet]. Medical News Today. Available from: https://www.medicalnewstoday.com/articles/281703.php
* ↑ Arthritis as a Potential Barrier to Physical Activity Among Adults with Obesity --- United States, 2007 and 2009 [Internet]. Available from: https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6019a4.htm
* ↑ Lynda F. Voigt, Thomas D. Koepsell, J. Lee Nelson, Carin E. Dugowson and Janet R. Daling. Smoking, Obesity, Alcohol Consumption, and the Risk f Rheumatoid Arthritis. Epidemiology, Vol. 5, No. 5 (Sep., 1994), pp. 525-532.
* ↑ Lu B, Hiraki L, Sparks J, Malspeis S, Chen C, Awosogba J et al. Being overweight or obese and risk of developing rheumatoid arthritis among women: a prospective cohort study. Annals of the Rheumatic Diseases. 2014;73(11):1914-1922.