Obesity and Chronic Pain

New Zealand has the third highest rate of obesity in the OECD with one in three affected. Obesity has a dose-response relationship with chronic pain with low back and knee pain being the most common, as well as multi-site pain. In those with morbid obesity (BMI > 40) only a minority do not live with chronic pain. Weight loss through dietary intervention can improve pain, particularly low back and lower limb pain. 
== Rates of Obesity ==
The rates of obesity have been increasing in New Zealand. In the New Zealand Health Survey 2020/2021, 34.3% of people over aged 15 were obese. This is an increase from 31.2% in 2019/2020. Similarly childhood obesity has also been increasing and was 12.7% in 2020/2021Obesity statistics | Ministry of Health NZ
There are drastic differences between ethnicities. Obesity was found in 71.3% of Pacific, 50.8% of Maori, 31.9% of European/Other, and 18.5% of Asians. There was a 1.6 times higher rate of obesity in those living in socioeconomically deprived areas.
== Obesity and Chronic Pain Correlations ==
Several studies have found strong associations between obesity and chronic pain.
* A Danish population study found that chronic pain defined as greater than 6 months of duration was found in 22% of those with normal weight, 29% in overweight, and 40% in obesity.Dansie EJ, Turk DC, Martin KR, Van Domelen DR, Patel KV. Association of chronic widespread pain with objectively measured physical activity in adults: findings from the National Health and Nutrition Examination survey. J Pain. 2014 May;15(5):507-15. doi: 10.1016/j.jpain.2014.01.489. Epub 2014 Jan 23. PMID: 24462501.
* A USA study looked pain experienced "yesterday," and this was reported in 19% of those with normal weight, 22% of those overweight (OR 1.7 - 3.5), and 28-44% of obese (OR 1.7 - 3.5). (Figure 1)
* A CDC study found that doctor diagnosed arthritis was present in 16% of normal weight, 23% of overweight, and 31% of obese adults.US Department of Health and Human Services. National center for chronic disease prevention and health promotion division of adult and community health. https://www.cdc.gov/arthritis/data_statistics/arthritis-related-stats.htm
* A USA survey of 6796 subjects found that low back pain was present in 3% of those with normal weight, 5% who are overweight, and 7-12% of those with obesity.Smuck M, Kao MC, Brar N, et al. Does physical activity influence the relationship between low back pain and obesity? The Spine Journal : Official Journal of the North American Spine Society. 2014 Feb;14(2):209-216. DOI: 10.1016/j.spinee.2013.11.010. PMID: 24239800.
* A UK study of 5752 GP patients found an odds ratio of 1.5 for overweight and 2.21 for obesity. Underweight also had an increased OR of 1.27. For intensity, disability, and chronicity 30% was attributed to abnormal BMI, 40% to deprivation, and 57% to the combined effects of BMI and deprivation.Webb R, Brammah T, Lunt M, Urwin M, Allison T, Symmons D. Prevalence and predictors of intense, chronic, and disabling neck and back pain in the UK general population. Spine (Phila Pa 1976). 2003 Jun 1;28(11):1195-202. doi: 10.1097/01.BRS.0000067430.49169.01. PMID: 12782992.
* The very large Norwegian HUNT study looked at subjects with no pain at baseline and followed them up over 10 years. Obesity was found to have odds ratios of 1.26-1.29 for arm pain, 1.2 for neck shoulder and back pain, 4.37 for knee pain in women, 2.78 for knee pain in men, 1.4 for hip pain (no clear association), and 1.79 for fibromyalgia. Exercising in the presence of obesity did alter the risk of osteoarthritis.Mork PJ, Holtermann A, Nilsen TI. Effect of body mass index and physical exercise on risk of knee and hip osteoarthritis: longitudinal data from the Norwegian HUNT Study. J Epidemiol Community Health. 2012 Aug;66(8):678-83. doi: 10.1136/jech-2011-200834. Epub 2012 Apr 17. PMID: 22511797.
* An Irish study of 915 individuals with an average BMI of ~50 found a prevalence of chronic pain of 91%. Knee pain was seen in 58% and low back pain in 69%.
There have also been a number of meta-analyses
* A meta-analysis of 33 studies found an odds ratio of 1.5 for obesity and low back pain.Shiri R, Karppinen J, Leino-Arjas P, Solovieva S, Viikari-Juntura E. The association between obesity and low back pain: a meta-analysis. Am J Epidemiol. 2010 Jan 15;171(2):135-54. doi: 10.1093/aje/kwp356. Epub 2009 Dec 11. PMID: 20007994.
* A meta-analysis of 26 studies found an odds ratio of 1.4 for obesity and lumbar radicular pain. There was also increased rates of hospitalisation and surgery.Shiri R, Lallukka T, Karppinen J, Viikari-Juntura E. Obesity as a risk factor for sciatica: a meta-analysis. Am J Epidemiol. 2014 Apr 15;179(8):929-37. doi: 10.1093/aje/kwu007. Epub 2014 Feb 24. PMID: 24569641.
== Pathophysiology ==
There are several potential mechanisms for the pathophysiology of pain in obesity
* Direct mechanical effect on weightbearing joints such as the knees. For example each kilogram of weight loss results in 4 kilograms of less load on the knee per step.Messier SP, Gutekunst DJ, Davis C, DeVita P. Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum. 2005 Jul;52(7):2026-32. doi: 10.1002/art.21139. PMID: 15986358.
* Adipokines, leptin, and inflammatory proteins released by adipose tissue.
* Genetic clusters: depression, obesity, and chronic conditions with pain
* Poor general health
* Reduced physical activity
* Psychosocial and environmental factors
== Weight Loss Outcomes ==
Weight loss reduces both pain and disability in patients with knee osteoarthritis. For example, in the IDEA trial, an RCT of 399 overweight and obese adults with knee osteoarthritis, diet-induced weight loss of 10% or greater body weight plus physical exercise for 18 months was more effective than each intervention alone. Baseline pain scores were 6.1/10. The diet plus exercise group score was 3.6 with a mean weight loss of 11.4%, diet alone was 4.8/10 with weight loss of 9.5%, and exercise alone was 4.7/10 with weight loss of 2%.
A meta-analysis of 19 RCTs in patients with knee or hip osteoarthritis found that weight reduction results in a small to moderate improvement in pain and function.Robson EK, Hodder RK, Kamper SJ, O'Brien KM, Williams A, Lee H, Wolfenden L, Yoong S, Wiggers J, Barnett C, Williams CM. Effectiveness of Weight-Loss Interventions for Reducing Pain and Disability in People With Common Musculoskeletal Disorders: A Systematic Review With Meta-Analysis. J Orthop Sports Phys Ther. 2020 Jun;50(6):319-333. doi: 10.2519/jospt.2020.9041. Epub 2020 Apr 9. PMID: 32272032.
== Bariatric Surgery Outcomes ==
Bariatric surgery may be effective in improving chronic pain, at least in the short term. 
Short term data 
For example one study of 48 patients with mean post-surgical weight loss of 41 +/- 15kg found that musculoskeletal complaints reduced from 100% prevalence down to 23% at one year.
A study of 2458 patients with back and leg pain found that weight loss with bariatric surgery at one year resulted in 75% of patients having a clinically meaningful reduction in hip and knee symptoms, 50% had a reduction in bodily pain, and 75% had increased function. At three years 45% had reduced bodily pain and 70% had increased function. (Figure 2)
Another study of 2862 patients found that bariatric surgery resulted in 80% reporting improvement in hip pain, and 75% reporting improvement in knee pain. at one year The effect was greatest in those with moderate to severe symptoms. (Table 1)
Table 1. Degree of hip and knee symptoms at baseline and one year after Roux-en-Y Gastric Bypass for 1930 patients.
 	Hip Baseline	Hip One Year Post-op	Knee Baseline	Knee One Year Post-op
No Symptoms 	42.4% 	73.8% 	15.4% 	62%
Mild Symptoms 	23.2% 	15.8% 	26.7% 	24.6%
Moderate Symptoms	21.5% 	7.5% 	29.3% 	9%
Intense Symptoms 	12.9% 	2.9% 	28.5% 	4.4%
Longterm data
Longer term studies are less rosy for bariatric surgery as a treatment for pain. It appears that over time analgesic use steadily increases to levels above baseline by year 7. A New Zealand study found analgesic use steadily increased, reaching a 50% increase in prescribing at 5 years 
Another study looked at overall pain rates, and this did improve over the first 2 years, but then deteriorated from 2-5 years and then slightly improved from 5-7 years. The study found that greater pain was associated with less weight loss and greater weight regain over time.
A study 304,157 severely obese adults, including 6212 bariatric surgery patients, looked at overall disease rates over time following bariatric surgery. After 5 years with a median of 9.9 years, there were the following changes.
* Decreased prevalence: CKD (0.45), CVD (0.49), diabetes (0.51), IBD (0.75), asthma (0.79), cancer (0.79), CHF (0.79)
* Increased prevalence: peptic ulcer (1.99), alcohol misuse (1.55), frailty (1.28), severe constipation (1.26), sleep disturbance (1.21), depression (1.81), chronic pain (1.12).
However when looking at lower limb pain there does appear to be a long term benefit for pain.
== See Also ==
* Knee Osteoarthritis
* Hip Osteoarthritis
== References ==
Category:Lifestyle