This blog is a request of my Aunt who asked if I could post anything relating to obesity and extra wear and tear on the the joints (aka osteoarthritis). It’s considered common knowledge in medicine that obesity increases the risk for arthritis, and I hear my physical therapy patients frequently say that their knees or hips would feel better if they lost weight. So I thought it would be interesting to see exactly how much weight actually effects arthritis. Two relatively recent studies appeared to best answer the question being as follows:
Abstract
BACKGROUND:
Obesity is one of the most important risk factors for osteoarthritis (OA) in knee(s). However, the relationship between obesity and OA in hand(s) and hip(s) remains controversial and needs further investigation. The purpose of this study was to investigate the impact of obesity on incident osteoarthritis (OA) in hip, knee, and hand in a general population followed in 10 years.METHODS:
A total of 1854 people aged 24-76 years in 1994 participated in a Norwegian study on musculoskeletal pain in both 1994 and 2004. Participants with OA or rheumatoid arthritis in 1994 and those above 74 years in 1994 were excluded, leaving n = 1675 for the analysis. The main outcome measure was OA diagnosis at follow-up based on self-report. Obesity was defined by a body mass index (BMI) of 30 and above.RESULTS:
At 10-years follow-up the incidence rates were 5.8% (CI 4.3-7.3) for hip OA, 7.3% (CI 5.7-9.0) for knee OA, and 5.6% (CI 4.2-7.1) for hand OA. When adjusting for age, gender, work status and leisure time activities, a high BMI (> 30) was significantly associated with knee OA (OR 2.81; 95%CI 1.32-5.96), and a dose-response relationship was found for this association. Obesity was also significantly associated with hand OA (OR 2.59; 1.08-6.19), but not with hip OA (OR 1.11; 0.41-2.97). There was no statistically significant interaction effect between BMI and gender, age or any of the other confounding variables.CONCLUSION:
A high BMI was significantly associated with knee OA and hand OA, but not with hip OA.
Abstract
Osteoarthritis (OA) is a leading cause of pain and disability and leads to a reduced quality of life. The aim was to determine the current evidence on risk factors for onset of knee pain/OA in those aged 50 and over. A systematic review and meta-analysis was conducted of cohort studies for risk factors for the onset of knee pain. Two authors screened abstracts and papers and completed data extraction. Where possible, pooled odds ratios (OR) were calculated via random effects meta-analysis and population attributable fractions (PAFs) derived. 6554 papers were identified and after screening 46 studies were included. The main factors associated with onset of knee pain were being overweight (pooled OR 1.98, 95% confidence intervals (CI) 1.57-2.20), obesity (pooled OR 2.66 95% CI 2.15-3.28), female gender (pooled OR 1.68, 95% CI 1.37-2.07), previous knee injury (pooled OR 2.83, 95% CI 1.91-4.19). Hand OA (pooled OR 1.30, 95% CI 0.90-1.87) was found to be non-significant. Smoking was found not to be a statistically significant risk or protective factor (pooled OR 0.92, 95% CI 0.83-1.01). PAFs indicated that in patients with new onset of knee pain 5.1% of cases were due to previous knee injury and 24.6% related to being overweight or obese. Clinicians can use the identified risk factors to identify and manage patients at risk of developing or increasing knee pain. Obesity in particular needs to be a major target for prevention of development of knee pain. More research is needed into a number of potential risk factors.
My comments:
The two papers look at the issue of osteoarthritis, obesity and other risk factors and come to similar but somewhat different conclusions, which is the norm for medical research. The first paper found that obesity defined as a BMI of >30 increased the risk of developing knee arthritis 2.81 times. The risk of hand arthritis was increased almost the same at 2.59 times, while the risk of hip arthritis was increased only 1.11 times (which surprised me) and was not statistically significant. So it’s interesting to note that obesity over the 10 year study period had little to no effect on the hips, but considerable effect on both the knee and hands. In this paper the researchers did note that other studies did associate obesity with hip arthritis and with an odd ratio of ~2.0 which indices double the risk.
The second paper pooled the results from a number of other studies looking directly at the knee, and found being overweight (defined as a BMI between 25-30) increased the risk of developing knee arthritis 1.98 times, obesity (BMI >30) 2.66 times. Female gender increased the risk 1.68 times and a previous knee injury increased the risk 2.83 times, with hand arthritis increasing the risk of having knee arthritis 1.3 times, the latter of which was not significant.
So there is still some question regarding quantifying effects of obesity on the development of osteoarthritis and with researchers generally measuring inputs, outcomes and time frames a little different. The take home seems to be that obesity increases the risk of knee arthritis 2-3 times, hand arthritis ~2.5 times and hip arthritis somewhere between no effect and maybe 2 times. The results were given with in the form of odds ratios, which implies association but not causation. Obesity might cause knee arthritis first making you move less, lessening the effects on the hips, but making getting up and out of chairs more difficult stressing the hands as you push off. While that explanation is logical sounding, and potentially correct, it’s something I just made up off the top of my head as I write this but according to the CDC knee replacements outnumber hip replacements by more than 2 to 1 so maybe I guessed right. Still from your joints perspective, it seems good to eat less and exercise more.
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