An extra layer of fat won't provide a cushion against pain -- in fact, obese people are more sensitive to pressure pain than those who are not overweight, and they are equally susceptible to extremes of hot and cold.
A new study, carried out at Leeds Beckett University, highlights the differences in pain response between different groups of people. The results could reinforce the argument for weight loss programmes being part of pain management plans for obese people suffering from chronic pain.
The team investigated 74 volunteers, categorised as obese, overweight or normal according to their body mass index (BMI) -- a standard way of measuring if a person is at a healthy weight for their height.
Volunteers in each group had pressure, cold and heat applied to two different areas of the body. The first experiment tested the hand, at the base of the thumb, an area that has little body fat. The second measured responses near the waist, in an area where extra fat is stored. Volunteers were asked to report at what point the pressure, cold or heat first felt painful.
Each volunteer was also asked to report their experience of cold pain by putting their hands into icy water. Again, they were asked to report the point at which they felt pain.
In the obese group, volunteers reported feeling pain from pressures equivalent to around 4.3kg per square centimetre, while those in the group with normal BMI reported pain at about 8.6kg per square centimetre. Interestingly, the middle group, those classed as 'overweight', had a slightly higher pressure pain threshold than the 'normal' group, with pain being reported at 10kg per square centimetre.
In terms of response to hot and cold temperatures, there was no significant difference across any of the groups, when tested at the waist. Only a small increase in sensitivity was reported in tests on the hand, suggesting that an extra layer of fat is no protection against extreme temperatures.
"Obese people are more likely to experience pain from factors such as the mechanical impact of increased weight on joints than people with a normal BMI," explains Dr Osama Tashani, a senior research fellow at the Centre for Pain Research at Leeds Beckett University. "But our study suggests that even in areas of the body which are not bearing weight, obese people are more susceptible to pressure pain."
"The overweight group had the highest pressure pain threshold, which might be because there were more people in this group taking part in physical activities, which could also affect how a person feels pain," says Dr Tashani.
The results, published in the European Journal of Pain, show that obese people are likely to have the lowest pressure pain threshold -- but it could also suggest that those with a low pressure pain threshold are more likely to become obese. "It could be the case that a person who is more sensitive to pain is less likely to do physical activity and therefore more likely to gain weight and become obese," says Dr Tashani.
The team plan to carry out further research into the factors that make people more susceptible to pain. This includes examining the chemicals secreted by fatty tissues in the body which could affect the response of pain receptors.
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Tashani, O. A., Astita, R., Sharp, D., & Johnson, M. I. (2017). Body mass index and distribution of body fat can influence sensory detection and pain sensitivity. European Journal of Pain. DOI: 10.1002/ejp.1019