The Pathway between Non-communicable Diseases and Socioeconomic status
Author:Amano Hoichi M.D.
Graduate School of Public Health, Teikyo University
Editor:Akihiko Ozaki M.D.
The number of non-communicable diseases, despite being able to be prevented, has been increasing around the world.
According to the World Health Organization (WHO), health burden caused by non-communicable diseases (NCDs) has been consistently on the rise. NCDs are defined as a spectrum of diseases which are caused by unhealthy lifestyles such as high sodium intake, high alcohol intake, smoking, lack of exercise, obesity and so on. In general, hypertension, diabetes, chronic kidney disease (CKD), stroke, coronary heart disease (CVD) and malignant tumors are considered as NCDs. In 2008, of the 57 million deaths worldwide, 36 million (63%) were caused by NCDs. WHO also predicts that the number of deaths due to NCD will increase to 55 million by 2030.
What is the term “SES”?
The term socioeconomic status (SES) refers to differences in possession of properties and resources between individuals and groups. Well-accepted indicators of SES are individual/household income, education, and occupation.
Recently, researchers have keenly investigated whether socioeconomic status (SES) is associated with metabolic unhealthy lifestyles, and the development of NCDs.
1. It is reported that “household expenditure” is associated with health. When household expenditure is divided into four groups, the lowest group of household expenditure has 1.3-1.5 times the risk of obesity, hypertension and a high level of blood glucose, compared with those in the highest group. In our study, which was performed in Japan, a smaller amount of income was associated with an approximately 30% increase in the risk for CKD.
2. Education is also associated with unhealthy lifestyles. In one study performed in Japan, junior high school graduates were three times more likely to smoke compared with those who graduated from postgraduate schools. There could be association between education and mortality as well. Junior high school graduates have about 1.3 times the risk of mortality than those who graduated from universities.
3. In England, mortality risk among the adults differed according to social class (based on occupation). It is reported that a mortality of blue workers is higher than that of white color workers.
Further, associations between occupational class and multiple conditions are observed, including metabolic disorder, the risk of CVD, cognitive function (before dementia) and self-perceived health.
Why different social positions cause the NCD? What is the pathway?
It is imperative to understand why above-mentioned social inequalities could cause many kinds of disorders. In order to explain their possible pathways, it could be useful to learn “autonomic nervous system” and “hypothalamic - pituitary - adrenal cortical pathway”. In one hypothesis, the mental stress induced by low SES, such as low-income and labor-intensive occupations, could activate sympathetic nerve system. As a result, the levels of adrenaline and noradrenaline and/or inflammatory cytokine could be increased. These changes can further induce increases in blood pressure and pulse, stimulation of blood coagulation factors, dysregulation of immune function, release of accumulated free fatty acid, insulin resistance, coronary spasm, microcirculation disorder and so on. These hormonal and inflammatory cytokine changes can trigger diverse and possible critical conditions.
Let us introduce our study.
In a recent article published in Journal of Atherosclerosis and Thrombosis,
We examined a possible association between work schedules and inflammatory markers among Japanese workers. We categorized the participants into four groups according to their working schedule: regular work; shift work without night work; shift work with night work; and only night work.
In our study, the night shift work was significantly associated with higher levels of IL-6. IL-6 is a well-known inflammatory marker, and our works suggested that this marker could be considered as a previously-unknown risk factor for CVDs. We also found that insufficient sleep and circadian rhythm disturbances were much more common among night shift workers compared with other workers. It has been recently reported that the level of stress hormones could be increased among the population affected by sleep restriction and circadian rhythm disturbances. Such relationships would explain for increased IL-6 levels among night shift workers. These observations may help us decipher underlying mechanisms of the association between work schedules and CVD development.
Relationships between social inequalities and NCDs remains to be elucidated. However, we are gradually capturing that stress hormones and inflammatory cytokine may play vital roles. A complete elucidation of such relationships could contribute to a prevention of NCDs in future.
1, Associations of household expenditure and marital status with cardiovascular risk factors in Japanese adults: analysis of nationally representative surveys. J Epidemiol. 2013;23(1):21-7
2, Interleukin-6 Level among Shift and Night Workers in Japan: Cross-Sectional Analysis of the J-HOPE Study. J Atheroscler Thromb. [Epub ahead of print]