Obesity, or adiposity, is on a rise in America, and with this rise has come the increase of inflammation. Many Americans face obesity, but obesity has been heavily correlated with lower socioeconomic status. This leads to the question of whether socioeconomic status could be the driving force of having higher Body Mass Index (BMI) and thus having increased levels of inflammation in the body. Research is limited on diet and socioeconomic status correlations, but there are ways to adjust for diet, like looking at antioxidant levels. When looking for literature on this topic focus on articles that focused on weight, adiposity, antioxidant level, and if found, diet. Through this literature review it was found that BMI and inflammation are directly correlated. It is also noted that socioeconomic status (SES) and inflammation were inversely correlated.
Key Terms: “Inflammation,” “Interleukin-6,” “CRP,” “Adiposity,” “Obesity,” “BMI,” “Waist Circumference,” “Diet”
There have many promising studies on inflammation and the risk factors it creates for the general public, but there is still research to be done on how socioeconomic status affects adiposity which in turn affects inflammation. Obesity, or adiposity, is one of the leading epidemics in America, and it is not going to slow down anytime soon. Adiposity is one of the known causes of inflammation in the human body; it causes major problems like cardiovascular disease, type 2 diabetes, and other severly life threatening health issues. One major factor, in obesity, is socioeconomic status, which plays a huge role in many Americans’ daily lives. It has been noted that lower socioeconomic status has been correlated with higher levels of inflammation in the body, but does socioeconomic status influence Body Mass Index (BMI) which then raises levels of inflammation? Investigating the role socioeconomic status has on BMI can help find ways to combat the rising levels of inflammatory markers being found in people of lower socioeconomic status. This is a huge knowledge gap in behavioral immunology, that if filled could help people of lower socioeconomic status combat diseases.Therefore this literature review will look at current studies that look at socioeconomic status, BMI, and adiposity, in hopes of finding a causal link.
Inflammation is a series of mechacisms the body creates to fight off wounds or infections. It is mainly indicated by red swollen skin, puss coming from a wound, or sickness symptoms, such as: runny nose, headache, fever, and others. Inflammation of the body without wound or infection can occur due to stress in the body, adipocytes, and other behavioral factors. Key terms used in this article are Interleukin 6 (IL-6), C-reactive protein (CRP), and Body Mass Index (BMI). IL-6 and CRP are both inflammatory cytokines that act as inflammatory markers in the blood stream. BMI is a measurement of adiposity, which takes a person’s height and weight to calculate how obese they are, consequently when we get a measurement of obesity we also get a measurement of adiposity. Adiposity has long been linked to diseases, such as cardiovascular disease, this pathway could be a major link to how.
Most of the literature found in this review were obtained from the database PubMed and recommendations from Dr. Anna Marsland, PhD. University of Pittsburgh. The advanced search method was utilized and the key words “Inflammation,” “Interleukin-6,” “CRP,” “Adiposity,” “Obesity,” “BMI,” “Waist Circumference,” “Diet” had to appear in the articles used in some combination. Articles were discarded if they were older than 10 years old, but I did not reject studies from different countries, because most countries have a lower class population. Many of the articles were picked solely off of the criteria mentioned above, after reading the abstracts I decided if the information was relevant to my research.
Several of the studies reviewed noted that socioeconomic status (SES), which is usually measured through years of education or household income, has been inversely correlated with inflammation. O’Connor et al. (2009) found that concentrations of CRP are much higher in patients that have a lower SES. Janicki-Deverts et al. (2009), noted that lower SES was correlated with increased levels of oxidation and decreased levels of antioxidant nutrients. Lower levels of antioxidants indicate that the patients were not eating a healthy diet, mostly that of processed food which is known to increase BMI. High oxidation levels indicate that most of the patients were smokers; smoking is another pathway to increased inflammation in the body that we will not be looking at. Therefore lower socioeconomic status is associated with lower levels of antioxidants which in turn results in a higher BMI and higher inflammation.
Most of the studies reviewed talked about adiposity and its role in inflammation. Adipocytes, fat cells, create adipose tissue and as a result causes adiposity, or obesity. Adipocytes have recently been discovered to have immune like characteristics, and in fact make macrophages–immune cells that cause inflammation. Most of the studies agreed that adipocytes have immune function and can create macrophages (Singh and Newman 2011), (Schlecht et al. 2016), (Mraz and Haluzik 2014), and (O’Conner et al. 2009). When there is an increase of adiposity in the body, there is an increased number of adipocytes making macrophages. These macrophages are also giving off inflammatory markers which stimulate an inflammatory response in the body–which has been associated with increased risk for cardiovascular diseases. Two studies focused on the different kinds of adipose tissue, visceral and subcutaneous, but for both types of fat tissue it was concluded that with an increase of adiposity there was an increase of inflammatory markers (Schlecht et al. 2016), and (Mraz and Haluzik 2014). Also in the O’Conner study it was seen that a decrease in BMI, whether it be from weight loss or liposuction, led to a massive decrease in inflammatory markers circulating in the blood.
All of the literature in this review defines inflammation as a cascade of mechanisms used to fight off infections and heal wounds. Mainly the studies were focusing on interleukin-6 (IL-6) and C-reactive protein (CRP), which are the most common inflammatory markers and indicators for future risk (Singh and Newman 2011), (Mraz and Haluzik 2014), and (Schlecht et al. 2016). These inflammatory markers are called cytokines and they are produced from immune cells in the body. In the studies looked at, it was conclusiley decided that inflammation was correlated inversely with SES and directly with adiposity (Mraz and Haluzik 2014), and (Schlecht et al. 2016). However there were some disparities on which inflammatory markers were affected by these different variables. CRP and IL-6 were seen to increase with lower SES and also with increased levels of adiposity.
Studies looking at diet seemed to agree that a diet high in antioxidants–such as a Mediterranean Diet–were associated with lower levels of inflammation. They included diets low in processed foods- Western diet is high in processed food- which could decrease BMI. It was correlated that people of lower SES were less likely to have a diet high in antioxidants than their counterparts with higher SES ( Kiecolt-Glaser et al. 2017), ( Kiecolt-Glaser 2010), (O’Conner and Irwin 2010), and (Mozaffarian 2015).
The studies all had different numbers of participants, the highest having 5000 participates. Regardless of size the correlations between SES and inflammation were still seen, along with the correlations between adiposity and inflammation. The O’Conner et al. (2009) article seemed to have the most reliable data, because it looked at the different kinds of adipose tissue to make the assertion that adiposity is in fact correlated heavily with inflammation. It also controlled the important variables that could have a huge impact on inflammatory markers- such as smoking and stress. While the others also controlled for these variables, they did not look closely at the different kinds of adipose tissue and how that could affect the levels of inflammation in the body. The studies seemed to all be in agreement that SES and inflammation are inversely related, and BMI (or adiposity) is directly related to inflammation. But most of the studies did not look at whether adiposity was the link between lower socioeconomic status and inflammation.
Increased levels of inflammatory markers are seen in the body when levels of adiposity are increased and level of SES is decreased. When in high concentrations, inflammatory markers can be used to predict the onset of disease and even mortality. But researchers are still not sure what is the causal link between SES, BMI, and inflammation–which is important to find because measures could be taken to prevent people of lower SES from food insecurity, and other factors that increase inflammation. Researchers understand that there are heavy correlations between SES, BMI, and inflammation, and have found that lower SES correlates with increased inflammation and higher BMI correlates with increased inflammation. This could mean that because people of lower SES have food insecurity and often eat meals high in processed food, they have higher BMIs than their counterparts with higher SES, and that because they have higher BMI they also have increased levels of inflammation in the body. One major limitation to this review is that there are very little accurate studies on diet, due to people not being able to recall what they have eaten, and the amount of food they have eaten.