Pain & Weight Part 1 – Summary

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Pain & Weight Part 1 – Article

Pain and adolescent and childhood obesity.

Sadly, it’s not just adults who suffer from increased prevalence of pain when carrying excess weight. Similar results have been shown in adolescents and children; basically, in all age groups. Obesity is significantly associated with the presence and extent of pain complaints in the young. As of 2011 there is reported to be ~43 million children worldwide under the age of five being reported as overweight.48

Unfortunately, that number doesn’t decrease as they get older. In Australia, obesity, as defined by WHO, continues to be a major public health problem with over 20% of school children being either overweight or obese49 and children from low socioeconomic areas being 70% more likely to be either overweight or obese.50

So, let’s see how this relates to pain and if it’s limited to certain age groups.

A study published in 2011 estimated overall and age-specific associations between obesity and musculoskeletal pain in children.51 It found a significant increase in pain in the lower extremities of extremely obese children across three age
ranges encompassing children aged between 2 and 19 years compared with normal-weight children.

Researchers examined whether obesity is associated with reporting of musculoskeletal pain.52 They looked at chronic regional pain (CRP) which is limited to a particular area of the body and chronic widespread pain (CWP) which is in multiple areas of the body. 3376 participants, with an average age of 17, were studied. 44.7% of participants reported any pain within the last month lasting 1 day or longer; 16.3% reported lower back pain, 9.6% shoulder pain, 9.4% upper back pain, 8.9% neck pain, 8.7% knee pain, 6.8% ankle/foot pain, 4.7% CRP, and 4.3% CWP.

Only 7.0% of participants were obese and obesity was associated with increased odds of reporting any pain. Compared with non-obese participants, those with any pain, knee pain, and CRP reported more severe average pain. Obese adolescents were also more likely to report musculoskeletal pain, including knee pain and CRP. Moreover, obese adolescents with knee pain and CRP had relatively high pain scores which can potentially lead to a worse outcome.

In another study 7,373 adolescents aged 13 to 18 years participated and overweight and obesity were associated with increased odds of pain.53 Pain was evaluated as chronic non-specific pain, chronic multisite pain, and chronic pain with high disability.

One study found that an increase in fat distribution across the body is related to foot pain, and yet this relationship is not evident with an increase in muscle mass.54 This means it is not due to increasing weight. Similarly, a Dutch study
identified that overweight and obese children self-reported ankle and foot problems.55 Another study examined orthopedic complications in overweight children and adolescents and found a significantly higher prevalence
of skeletal fractures compared with non-overweight subjects.56

More concerning is a study that reports the joint changes in obese children who had a BMI above the 95th percentile with significantly higher reports of pain when compared with normal weight children.57 These changes include a 55.1% higher frequency of genu valgum, commonly called ‘knock-knee’, and a 24.2% higher frequency of genu recurvatum (excessive extension of the knee-joint) in obese children compared with the 2% occurrence in the control group of normal-weight children.

These studies indicate a serious risk to the skeletal system of a child who is either overweight or obese as well as the pain associated with musculoskeletal dysfunction and deformity. There is a linear relationship observed as the odds of having joint pain increased by 10% for every 10-kg increase of weight and an increase of 3% for every unit increase in BMI.58,59

As you may have noticed, it’s my goal to provide some good news after reporting so much sobering data. Unfortunately, I was unable to find any research that has looked at weight loss in the young and how that weight loss affects pain. What I did find was overwhelming data that looked at weight loss strategies in the younger population.

There is a huge amount of research that has looked at how successful or unsuccessful weight loss strategies are; including risks and side effects of specific measures used for weight loss; such as medications. I could find none that looked at improved reporting of pain; however, there is a lot of data that shows weight loss in adults relates to improved pain issues. I would expect this would also occur in a younger population; it just appears that we haven’t looked into this specific outcome yet in the research world.

Obesity and pain sensitivity.

Does being overweight or obese lead to increased pain sensitivity? Let’s look at what the data shows.

I looked at mice and rat studies as those are quite common in the research world in an attempt to better understand human issues. I also looked at human studies since we are, in fact, human beings.

In the mice and rat study reviews it appears that physiological changes, not just weight gain, appear to be responsible for the changes in how the nociceptors (pain cells) respond to stimuli. Physiological changes that have been observed include inflammation levels, blood glucose levels, and A1C levels.74,75

In the human studies, which are more appropriate and useful, multiple body areas have been tested for increased pain sensitivity. and it appears certain body areas show increased sensitivity and others do not. In fact, some studies showed less sensitivity which does tend to confuse things.

One study looked at the pressure pain threshold (PPT) of two locations, triceps and inguinal (hip area) lines, using a digital pressure algometer.76 Men with central obesity and moderate leisure time physical exercise were seen to be more sensitive to muscle mechanical stimuli. Elevated PPT was also found among subjects with hyperglycemia both in triceps and inguinal line areas. Interestingly, those subjects exhibiting excess drinking; elevated PPT was reported only for triceps.

Obesity was related significantly to greater pain sensitivity to palpation of known tender points for fibromyalgia, particularly in the lower body areas.77 If you remember I shared a term called hyperalgesia which is when pain cells become hypersensitive to normal pressure or touch. When measuring tolerance to pressure and the first occurrence of pain obese subjects were significantly more pain sensitive.78 This sensitivity was assessed when pain first occurred with a 3-pound weight pressing on the index finger.

Obesity is seen to increase the risk of peripheral neuropathy which is a result of damage to your peripheral nerves, often causing weakness, numbness, and pain, commonly in your hands and feet.79 It can also affect other areas of your body.

On the flip side of this topic there are studies showing patients with more fat tissue have higher pain sensitivity thresholds than people of normal weight, as they were found to feel less pain to a needle placed on the forearm skin.80 There are also studies that show sensation to cold and warm are decreased in abdominal areas that have increased fat tissue.

Since there appears to be such discrepancy in these studies; some showing increased pain sensitivity and some showing decreased pain sensitivity; we will need to look at this data a little closer and sort it out somehow to better understand why.

A 2013 study published in the European Journal of Pain,81 I believe, helps to explain some of the confusion. This study looked at multiple areas of the body in both obese and normal weight subjects. What they found is that areas of excess
subcutaneous fat were the areas with decreased sensitivity. The areas where there was little fat, such as the forehead, confirmed no statistically significant difference in the reporting of pain sensitivity.

Obesity and post-operative pain.

The Obesity Paradox.
Have you heard of this? This is what is seen when looking at post-operative complications and a patient’s weight. While obesity alone is a significant risk factor for wound infection, more surgical blood loss and a longer operation time; it is the underweight patient who is most at risk of major postoperative complications, including long-term mortality.82

Being obese is associated, in some studies, with improved long-term survival, validating the obesity paradox as complication and mortality rates are significantly worse for underweight patients. Before celebration for being overweight begins; let me remind you of many important facts. Being obese is associated with an increased risk of a number of medical conditions and reduced life expectancy which are presented in other modules. Obesity also reduces quality of life which is covered later in this document. There are also studies showing morbidly obese patients had a higher mortality rate, prevalence of tracheal reintubation, and cardiac arrest.83

When looking at long term results from hip replacement surgery, there was found to be no statistically significant difference in the improvement in scores for quality of life between the non-obese and obese groups. It is interesting to note that the preoperative quality of life score for both groups was similar as well. I mention this because there has been research data that has influenced surgeons to refuse to perform joint replacements for obese persons. These reasons were mentioned earlier. Obesity is seen to be a significant risk factor for wound infection, more surgical blood loss and a longer operation time.

The majority of studies found were focused on complication risks. Obese patients are reported to have a significantly higher risk of postoperative myocardial infarction, wound infection, nerve injury, and urinary infection. This is an important issue; yet does not provide an answer for those requiring surgery who are unable to lose weight prior to surgery.

Of course, our focus here is the pain factor, so let’s see what is found in the literature about pain and how it affects post-operative recovery in the obese population.

Managing post-operative pain is found to be a serious challenge in the obese population for multiple reasons. The bodily changes in function such as other medical conditions and the high prevalence of obstructive sleep apnea (OSA) amongst obese patients make providing effective and safe pain management difficult.84

Advice to better and more safely manage post-op pain includes multimodal analgesic therapy which involves the use of different classes of analgesics and different sites of analgesic administration to provide superior dynamic pain relief with reduced analgesic-related side effects. Other recommendations are a preference for regional techniques, avoidance of sedatives, non-invasive ventilation with supplemental oxygen, early mobilization and elevation of the head of bed to 30 degrees. Post-op monitoring requirements show different needs for safety as well. Sedation scoring is very important as is a low threshold for continuous pulse oxymetry, arterial blood pressure measurement and ensuring overall close monitoring for the postoperative period.

For obese patients with OSA, sedatives, opioids, and anesthetics alter airway tone which increases the risk of chronic hypoventilation leading to elevated carbon dioxide (CO2) levels in the blood. There is also an increased risk for aspiration and acute airway obstruction after extubation. Airway obstruction and death has been reported in OSA patients with minimal doses of sedatives and anesthetics. This is a very serious issue, and it is critical to know these risks before going in for surgery. 

Obesity, sleep disturbance, and pain.

It is commonly known that chronic pain disrupts sleep. The National Sleep Foundation reports 1 in 3 persons loses more than 20 hours of sleep per month due to chronic pain.

Of those chronic pain patients who attend pain clinics 53% of them have clinically significant insomnia.85 Looking at it from the insomniacs’ viewpoint, over 40% report at least one chronic pain problem.

Let’s see how excess weight plays into these factors.

Aside from pain, a common sleep disturbance in obesity is obstructive sleep apnea (OSA).86 The strong relationship between obesity and OSA was already discussed in a previous chapter. This relationship is well documented, and the majority of those with OSA are obese. Considering pain, chronic pain patients with sleep apnea show reduced sleep duration and poorer sleep quality than those with sleep apnea without pain.87 Generally, obese patients are significantly more sleep disturbed than non-obese patients.

A substantial correlation between sleepiness and BMI is seen in obese women with fibromyalgia as compared to normal weight.88 Interestingly, sleepy women showed a greater weight gain after being diagnosed with fibromyalgia when compared to non-sleepy women.

There appears to be an interesting correlation between not getting enough sleep and gaining weight. Getting less than 6 hours per night is seen to increase the risk of becoming obese. To date, approximately 50 studies done in different geographical regions have examined the association between sleep and obesity in adults and children. The majority found a significant association between short sleep (generally <6 hours per night) and increased obesity risk.89-92

So, why does sleep loss matter?

Sleep is an important modulator of neuroendocrine function and glucose metabolism. This means sleep loss has been shown to result in altering metabolism and endocrine function. This includes decreased glucose tolerance, decreased insulin sensitivity, increased evening concentrations of cortisol, increased levels of ghrelin, decreased levels of leptin, and increased hunger and appetite.

To better explain how this affects weight gain, let’s look closer at these 3 hormones and how they are seen to relate to gaining weight:

Cortisol is a stress hormone that is known to promote fat storage.

An association between uncontrollable stress and abdominal fat distribution has been observed.93 Researchers investigated whether body fat distribution, determined by waist-to-hip ratio (WHR), is related to salivary cortisol levels in response to laboratory stressors.

Subjects were 41 overweight women with a Low or a High WHR. Multiple measures of cortisol and mood were obtained during a session of stressful tasks (eg., timed arithmetic) and during a time-matched, control rest session. Also, background life stress and psychological trait variables were assessed. Compared to Low WHR subjects, High WHR subjects secreted significantly more cortisol during the stressful session after 60 minutes of stress. This difference was not seen on the rest day. In terms of background and psychological measures, High WHR subjects were characterized by poorer coping skills and differences in mood reactivity.

Ghrelin is termed a hunger hormone because it stimulates appetite, increases food intake and promotes fat storage.

Your stomach makes ghrelin when it’s empty. Ghrelin is secreted primarily in the lining of the stomach, moves into the blood, crosses the blood-brain barrier, and ends up at your hypothalamus where it tells you you’re hungry.94,95 Ghrelin
levels are high before you eat and low after you eat.

Leptin inhibits hunger so decreasing this would seem to promote overeating and resultant weight increase.

Leptin is made by adipose tissue (fat) and is secreted into the circulatory system, where it travels to the hypothalamus. Leptin tells the hypothalamus that you have enough fat, so you can eat less or stop eating. Leptin may also increase metabolism, although there is conflicting research on this point.

Generally, the more body fat you have, the more leptin you make; the less food you’ll eat; and the higher your metabolic rate (possibly). Conversely, the less fat you have, the less leptin you have, and the hungrier you’ll be. Basically, for weight loss — the more leptin the better. Leptin was considered to be “the holy grail” of weight loss when it was first discovered in 1994 to turn fat mice into thin mice. The problem arose that it only helped in those who were genetically leptin deficient which was ~5% of obese subjects.

Closing this section about sleep disturbance with some good news requires me to share a meta-analysis of 18 studies.96

604,509 adults demonstrated a pooled obesity odds ratio of 1.55 for less than 5 h of sleep and a dose effect of sleep duration such that for each additional hour of sleep BMI decreased by 0.35 kg/m2. This means increasing the number of hours you sleep (if you are sleep deficient) could be a really good idea.

Obesity, function, quality of life, and pain.

Obesity is related to greater physical disability and psychological distress in chronic pain patients. 372 consecutive chronic pain patients seeking evaluation at a university pain clinic were divided into 3 weight categories based on body mass index (BMI). The categories were chosen to be normal (BMI < 25 kg/m2), overweight (BMI between 25 kg/m and 30 kg/m2), and obese (BMI > or = 30 kg/m2). Patients completed questionnaires to identify pain severity, disability, depression, anxiety, and quality of life.97

Pain severity and days per week with pain were similar among the weight groups; however, disability was related to increasing weight status, with increased BMI associated with more days per week with both reduced activity and complete disability. Physical function domain of quality of life was also reduced in relation to weight.98

Compared to non-obese patients, obese back pain patients appear to be more functionally impaired, have greater comorbid problems, and have more radicular symptoms than non-obese counterparts.99 Functional status was measured on 15,974 patients on an initial visit using a general physical health measure (SF-36 Physical Component Summary score) and a disease-specific measure (Oswestry Disability Index). General and disease-specific functional health status was significantly worse for patients with a higher body mass index. Obese patients also displayed more severe pain symptoms than nonobese spine patients.

A 7-year prospective cohort study of 34,754 employed men and women was conducted to determine the relative contribution of occupational risk factors, lifestyle factors, comorbidity, and psychological and social factors to the incidence of disability retirement because of back pain in the general working population.100

715 individuals (2.1%) were granted a back pain disability pension. BMI in the upper percentile was seen to be a predictor of back pain disability pension. To be fair the strongest predictors for future back pain disability were the occupational risk factor “physically demanding work” and the comorbidity factor “poor general health”. Factors other than BMI included “Feeling of being worn out” and current smoking.

Obesity is known to have various adverse impacts on people’s functional capacity and quality of life (QOL) in general.101 Mobility disability experienced by persons with obesity is also associated with reduced health related quality of life
(HRQOL) compared to persons without obesity.

In a 2007 JAMA report,102 researchers studied nearly 10,000 people ages 60 and older, measuring both functional limitations, such as the ability to stoop or kneel easily, as well as limitations in daily activity, such as being able to
carry a grocery bag or get dressed.

The study only looked at the disability risk from being obese, which means having a body mass index (B.M.I.) of 30 or higher. In the study, a person was considered to have functional limitations if they had trouble with four out of six tasks: walking a quarter of a mile; walking up 10 steps without resting; stooping, crouching or kneeling; lifting or carrying 10 pounds; walking between rooms on the same floor; and standing from an armless chair. A person was counted as having a daily limitation if they had problems with two out of three activities: getting in and out of bed, eating and dressing.

The extent to which individuals can function in daily life is central to their quality of life as they age. Simply being able to get in and out of bed easily or to stand up from a chair without assistance can sometimes mean the difference between living independently or needing to go to a nursing home. I worked in homecare and acute care for many years and there were many times it was necessary for someone to restore independent function after an illness or injury in order for them to be able to stay in, or return to, their own home.

Among obese individuals, the prevalence of functional impairment increased 5.4% between the 2 surveys, and ADL impairment did not change. At time 1 (1988-1994), the odds of functional impairment for obese individuals were 1.78 times greater than for normal-weight individuals.

At time 2 (1999-2004), this odds ratio increased to 2.75, because the odds of functional impairment increased by 43% among obese individuals during this period, but did not change among nonobese individuals. With respect to ADL impairment, odds for obese individuals were not significantly greater than for individuals with normal weight at time 1, but increased to 2.05 at time 2. This was because the odds of ADL impairment did not change for obese individuals but decreased by 34% among nonobese individuals.

Conclusions written were obese participants surveyed during 1999-2004 were more likely to report functional impairments than obese participants surveyed during 1988-1994, and reductions in ADL impairment observed for nonobese older individuals did not occur in those who were obese. Over time, declines in obesity-related mortality, along with a younger age at onset of obesity, could lead to an increased burden of disability within the obese older population.

Physical disability is a key indicator of morbidity and central to quality of life in aging. A substantial body of evidence from prospective investigations has confirmed that elevated BMI is a risk factor for physical disability among older adults.103 However, when the range of BMI has been sufficiently broad, being underweight poses as great a risk for physical disability as being excessively obese. The risk for physical disability from class I obesity remains inconclusive. (BMI 25 to 29.9)

The good news is weight loss plus exercise was seen overwhelmingly to positively affect physical disability of obese older adults; providing both higher self-efficacy and independence and lower reported pain experienced.

 References are available in the PDF download for this module.