Obesity is independently associated with chronic pain interfering with activities of daily living in adults: A cross-sectional population-based study

The present study demonstrated a strong association between chronic pain and obesity/morbid obesity in the South Australian population.

In today’s era, chronic pain has become a very common suffering, affecting people of all age groups across the world. It is particularly rising in the adolescents with incidence between 14-24%. The episodic pain lasting for more than three months is termed as “Chronic pain”. The World Health Organization (WHO) has reported that more than 1.9 billion adults globally were considered overweight, while 600 million people identified as obese in 2014. The WHO has also stated that obesity is not only a problem in well-established countries, but has greatly impacted low and middle income countries as well. Recent research studies have confirmed the link between obesity and many chronic pain concerns like musculoskeletal dysfunction, headaches and neuropathic pain. Also, some studies have shown that reduction in weight is significantly linked to the pain relief. Recently, a 5-year longitudinal study has verified a connection between fat mass, body mass index (BMI) and possibility of experiencing pain. Fat mass and BMI both were found to be associated with variety of chronic pain, but only BMI was found to be associated with lower back pain. The results are consistent with an 11-year longitudinal study in the elder patients that established the strong connection between obesity, chronic disease, ageing and chronic pain. While the pathophysiology of chronic pain is not clear, many studies have established that patients with both obesity and chronic pain are expected to face disability and effect on their daily activities. However, the mechanisms by which this association is facilitated are complex and variable.

Rationale behind the research:

• Most studies seeking to define the link between chronic pain and obesity do so from the view point of people who have contact with health services or else the studies are limited by the age of cohort considered or studied
• The present study was conducted aims to evaluate the link between chronic pain and obesity across the adult population, having controlled for other key factors

Objective:

The aim of this study was to examine whether obesity is independently associated with chronic pain that interferes with day-to-day activities in adults, irrespective of their health service contact, controlling for socioeconomic status, and other demographic factors.

Study outcomes:

Self-reported pain: Each respondent was asked, over the last six months, if he/she had “an episode of pain that has lasted more than three months”. The following options on a prompt card were given:

1. No
2. Yes, I did get pain but it did not interfere with my day-to-day activities
3. Yes, I did get pain and it interfered a little bit with my day-to-day activities
4. Yes, I did get pain and it interfered moderately with my day-to-day activities
5. Yes, I did get pain and it interfered extremely with my day-to-day activities

• BMI: It was derived from self-reported weight and height with answers accepted in metric or imperial measures. It was calculated using the formula, kilograms/metres², and recoded into three categories (underweight/normal weight, overweight and obese) as defined by WHO. The classification was used for people aged 15 to 17 years and recoded into three categories (normal weight, overweight and obese).

• Socio-demographic measures: Demographic variables included age, sex, rurality (metropolitan/rural), country of birth, highest level of education, marital status, gross annual household income and current work status

Outcomes

• One quarter of the respondents (24.6%; n=664) experienced an episode of pain that lasted more than three of the last six months. Of those people, 54.3% had pain that did not interfere or only interfered a little bit with their daily activities and 45.7% had pain that interfered moderately (25.6% or 6.5% of the total population) or extremely (n=18.7% or 4.7% of the total population) with their daily activities.
• Chronic pain interfering with day-to-day activities peaked in the population over 75 years of age. Three pain groups were compared by socio-demographic indicators and health conditions. Generally, respondents experiencing pain but no interference with their daily lives were more likely to be females of older age groups, widowed, and diagnosed with co-morbid illnesses. Respondents experiencing regular pain interfering day-to-day lives were more likely to be: obese, older, separated, divorced or widowed, having lower educational qualifications, living in a household with lower incomes, and diagnosed with current comorbid conditions.

Figure 1. Severity of pain impacting day-to-day lives of patients from different age groups

• Obesity and morbid obesity was seen in 21.6% (n=564) of the population. By age group, obesity peaked in the 45-54 year old age group where one third of all respondents were obese or morbidly obese. In the adjusted multinominal logistic regression model, compared to those with no pain, there was a strong association between obesity and pain that interfered moderately or extremely with day to day activities.

This study demonstrated that obese people were likely to have two-fold pain that interfered moderately or extremely with day-to-day activities, having controlled for key socio-demographic factors.

A recently published cross-sectional population study of 2508 people from Germany demonstrated very similar rates of chronic pain interfering with day-to-day activities for an association with obesity. Most population studies in this field highlight trends that chronic pain is more likely to be reported in females, elderly participants and those in lower socioeconomic settings, reflecting these findings from South Australia.

The present study provides supporting evidence to the growing body of research on the prevalence of chronic pain in the Australian population associated with obesity. Furthermore, more detailed assessment of attributes of obesity i.e. waist circumference and calculation of fat mass/free fat mass may help to further understand the aetiology of this combination of symptoms. Clinically, given evidence that weight loss can improve the management of osteoarthritis and its pain, understanding the genesis of the combination of pain and obesity, and recognizing its presence early plays a crucial role for all medical practitioners.