Physical activity, exercise, and chronic diseases

Chronic diseases are the leading cause of death worldwide with increasing prevalence in all age groups, genders, and ethnicities. Most chronic disease deaths occur in middle-to low-income countries but are also a significant health problem in developed nations. Multiple chronic diseases now affect children and adolescents as well as adults. Being physically inactive is associated with increased chronic disease risk. Global societies are being negatively impacted by the increasing prevalence of chronic disease which is directly related to rising healthcare expenditures, workforce complications regarding attendance and productivity, military personnel recruitment, and academic success. However, increased physical activity (PA) and exercise are associated with reduced chronic disease risk. Most physiologic systems in the body benefit positively from PA and exercise by primary disease prevention and secondary disease prevention/treatment. The purpose of this brief review is to describe the significant global problem of chronic diseases for adults and children, and how PA and exercise can provide a non-invasive means for added prevention and treatment.

Keywords: Chronic disease, Noncommunicable diseases, Obesity, Diabetes, Cardiovascular disease, Cancer, Physical activity, Exercise

Introduction

A chronic disease is an illness that is not contagious, usually of long duration, progresses slowly, and is typically a result of genetics, environment, or poor lifestyle .In 1990, more than 28 million (57%) of all global deaths were caused by chronic disease. This number increased to 36 million (63%) of all global deaths in 2008 and 39 million (72%) of all global deaths in 2016. Even though life expectancy estimates have consistently risen for the last two centuries, current estimations support a potential decline in life expectancy for future generations due to an increase in various chronic diseases such as lower respiratory disease, obesity, cancer, cardiovascular disease (CVD), diabetes, and stroke. Presently, the literature supports that the incorporation of daily physical activity (PA) and exercise into one's lifestyle will reduce risk for chronic diseases and mortality while providing a means for primary disease prevention. Furthermore, once a chronic illness is diagnosed, treatment is better managed when PA and exercise are part of the disease medical management plan. In either case of disease prevention or treatment, PA and regular exercise provide a higher quality of life and perhaps increased longevity.

Although altering disease risk factors reduces overall chronic disease risk, modifiable risk factors such as sedentary behavior are associated with an increased risk for chronic disease. Non-modifiable risk factors are traits that cannot be changed such as age, ethnicity, and genetics. However even though not altered directly, genes are strongly influenced by the environment and lifestyle affecting gene expression.  Modifiable risk factors are positively influenced by lifestyle such as daily PA, regular exercise, healthy diet, social engagement, spirituality, and stress management. However, other modifiable risk factors exist that are not directly related to lifestyle but negatively influence chronic disease risk such as education level, socioeconomic status, and employment. PA and regularly practiced exercise positively influence risk factors for chronic diseases such as CVD, type 2 diabetes, obesity, and cancer.  Thus, the purpose of this brief review is to describe the global chronic disease problem for adults and children, describe the social-economic impact of chronic disease, and how PA and exercise can provide a non-invasive role for added chronic disease prevention and treatment. To achieve this purpose, a literature search was conducted using Pubmed, Medline, and Google Scholar databases. Search terms used were physical activity, exercise, multiple chronic diseases, chronic disease prevalence measures, and healthcare economy. In addition, the reference lists from systematic reviews incorporating PA and exercise and chronic disease were also reviewed.

The Rise of Chronic Disease

Diseases have always plagued humans. Infectious diseases remain a primary focus for prevention and treatment. Over time, the incidence and mortality rates for infectious diseases have dropped with advancements of vaccinations, antibiotics, sanitation, and the development of procedures for general infectious disease prevention. The reduction of infectious diseases is associated with decreased morbidity and mortality resulting in an increase in life expectancy. However, unanticipated consequences followed the gain in life years including a shift in the world's health burden from infectious to non-communicable diseases (NCDs) such as CVD.

Many developing countries now experience the burden of both infectious and chronic disease rather than seeing a replacement of infectious disease with chronic disease. For example, India has the highest number of diabetic cases in the world  while also having the highest number of certain infectious diseases such as tuberculosis every year. In this same regard, infectious diseases in South Africa account for almost the same number of deaths as chronic disease.

In the past, chronic diseases were usually considered a problem only in developed countries.  However, 80% of deaths in low- and middle-income countries are now caused by chronic diseases. Low- and middle-income countries are shown to have four times the mortality rate from NCDs than high-income countries. Ischemic heart disease and stroke represented 85% of CVD deaths and 28% of all-cause mortality in developing nations. Diabetes prevalence is expected to increase from about 400 million to 600 million globally by the year 2035 with most of this increase occurring in low-to middle-income countries. Cancer prevalence crosses all global economic gaps with 57% of the reported cancer cases occurring in low-to middle-income countries and 43% in developed nations. In China for example, cancer is the leading cause of death and is accounts for 25% of all deaths.

Another global trend, especially in low-to middle-income countries, is the rate at which obesity prevalence has increased in recent decades. Currently, about 2 billion adults globally (approximately 25–33% of the world's population) are overweight and another 33% are obese. Obesity is associated with negative health implications and is a well-established risk factor for chronic diseases including CVD, type 2 diabetes, and certain cancers. In the United States, obesity prevalence (BMI ≥30) has more than doubled in the last two decades as has severe obesity (BMI ≥40). These trends lead to future predictions of a 33% increase in obesity and a 9% increase in severe obesity by 2030. Similar trends are seen across the globe. For instance, obesity prevalence in North and South America more than doubled between 1980 and 2015 with a 64% prevalence of overweight.  In Europe, approximately 60% of the population are considered overweight and 23% are obese.

Countries once unaffected by increasing obesity now struggle with elevated obesity rates. For example, China has reported a significant increase in the number of obesity cases.  While the proportion of the Chinese population classified as obese is relatively low (5%), China currently is ranked as second in the world with 250 million adults classified as overweight and another 40 million obese. Furthermore, the prevalence of overweight and obese children in China has more than doubled in the last 20 years. India has 135 million people affected by obesity with prevalence rates varying between states from 12 to 31%. These rates are expected to increase especially in middle-to low-income countries. Other obesity-related NCD rates such as CVD, type 2 diabetes, and cancer will also continue to rise and present a significant global health problem.