An in-depth investigation of the relationship between body fatness and pain sensitivity
Creators: name: Astita, Rehab
Publisher: name: Leeds Beckett University
Year: 2023
Subjects: Uncategorized

description: The aim of this PhD project was to investigate the relationship between pain sensitivity, body fat distribution and levels of pro-inflammatory cytokines. A systematic review of the literature retrieved 14 relevant articles from which 7 references were eligible to be selected for further consideration. There was a significant amount of heterogeneity across these 7 studies (Cochran’s Q=76; p=0.0001; I2=93.4%). There were only a small number of studies and those that existed were contradictory, had low methodological quality ratings and obesity measures were inadequate. It was concluded from the review that there was a need for more high quality studies using better obesity measures and more developed pain induction techniques such as quantitative sensory testing. The aim of the PhD’s project’s first experimental study was to compare the responses to experimentally induced thermal and mechanical stimuli between normal, overweight and obese individuals, categorised using their BMI, in the UK (n=74, 37 women). Repeated Measures Analysis of Variance (RM ANOVA) was performed on outcome measures using two sites of stimulation, the thenar eminence and suprailiac (waist) as a within subject factor, and sex and BMI groups as between subject factors. A regression analysis on sex, body fat percentage and BMI was also performed. The main finding of this experiment was that the pressure pain threshold of the obese group was significantly lower than normal weight and overweight groups. Obese individuals were also found to be less sensitive to thermal sensory detection thresholds. The aim of the second experiment was to investigate pain sensitivity response differences between obese and normal range BMI groups and correlate pain responses with four inflammatory biomarkers and body fat measurements obtained via a DXA scan method. In this study, measurements of pressure pain and cold pressor pain sensitivity response were taken from 38 participants (18 women). Biomarkers in venous blood were examined, and body composition (dual X-ray absorptiometry) was evaluated for each participant. It was found that pressure pain thresholds were significantly lower in the obese group compared with the normal BMI group, and forward regression suggested that high gynoid fat (g) was associated with lower pressure pain thresholds (β = -0.383, p=0.028), high lower limb fat (g) was associated with lower cold pain thresholds (β =-0.495, p=0.003), leptin was weakly associated with lower pressure pain threshold (r2=0.026) and counterintuitively high IL-6 was associated with higher cold pain tolerance (β=0.345, p=0.049). Women were also more sensitive to pressure pain (p=0.03). In conclusion, there is a need for high quality studies, using better obesity measures and more developed pain induction techniques that investigate the relationship between obesity and pain. The two experiments presented here contribute to knowledge by highlighting a possible correlation between obesity and pain sensitivity, suggesting that the pressure pain threshold of the obese group was significantly lower than normal weight and overweight groups. Obese individuals were also found to be less sensitive to thermal sensory detection thresholds. Furthermore, gynoid fat (g) and leptin were associated, albeit weakly, with pressure pain thresholds. All these relationships can be interpreted as a correlation between obesity and pain sensitivity rather than the view that one causes the other. The major contribution to knowledge of this thesis is that obese individuals categorized by their BMI are more sensitive to pressure pain, while subcutaneous fat is likely to affect pain sensitivity.