Fifth Phase of the Epidemiologic Transition: Title and subTitle BreakThe Age of Obesity and Inactivity

In 1900, Henry Ford unveiled the first car made in Detroit, the International Ladies' Garment Workers Union was founded in New York, and San Francisco was placed under a federal quarantine to prevent the spread of bubonic plague. Infectious disease was a major concern, and the most common causes of death in the United States and in many parts of the world at the time were pneumonia and tuberculosis. Today, most individuals die of cardiovascular disease or cancer. This dramatic shift in the illnesses that cause the majority of death and disability has been divided into 4 stages known as the epidemiologic transition.^{1 - 2} In the last 2 decades, however, a fifth stage, marked by an alarming increase in overweight and obesity and continued decreases in physical activity, has emerged. This ongoing trend is addressed by 2 articles^{3 - 4} in this issue of JAMA.

The first stage, which dominated most of human history, was characterized by pestilence and famine, when infectious disease and malnutrition kept average life expectancy at about 30 years. In the second stage, occurring in the late 19th and early 20th centuries in the United States and Europe, industrialization and urbanization led to increasing wealth and a corresponding increase in the availability of food, an era termed receding pandemics. As the century continued, public health systems and cleaner water supplies and sewage systems combined with better nutrition drove down deaths from infectious disease and malnutrition, leading to declining infant and child mortality and an increased life expectancy. The third stage, degenerative and human-made diseases, characterized by increasing mortality from cardiovascular disease and cancer, emerged in the mid 20th century. Smoking, decreased activity levels in the workplace and at home, and increased intake of animal products and fats resulted in increasing prevalence of elevated blood pressure and cholesterol levels. Age-adjusted cardiovascular disease and cancer rates were at their peak.

By the mid 1960s, the United States had entered the fourth stage of delayed degenerative diseases. Cardiovascular disease mortality declined, related to preventive strategies such as smoking cessation programs and effective blood pressure control, acute coronary care units, and technological advances that included coronary artery bypass surgery.⁵

Despite the many advances in preventive medicine and treatment that reduced cardiovascular disease, the new stage of the epidemiologic transition, the age of obesity and inactivity, emerged to threaten the progress made in postponing illness and death to later in adult life spans. The steady gains made in both quality of life and longevity by addressing risk factors such as smoking, hypertension, and dyslipidemia are threatened by the obesity epidemic.

Over the last 40 years, the proportion of the US population considered to be overweight (body mass index [BMI] ≥25.0) and obese (BMI ≥30.0) has steadily increased. In the 1960-1962 National Health Examination Survey, an estimated 31.6% of men and women met the definition for “pre-obesity” (BMI between 25.0 and 29.9), and 13.4% were obese.⁶ The latest prevalence and trends in obesity data from the National Health and Nutrition Examination Survey (NHANES), reported by Flegal and colleagues³ in this issue of JAMA, show that in 2007-2008, 68.0% of US adults were overweight, of whom 33.8% were obese. More men than women were overweight or obese, 72.3% compared with 64.1%.

If the increase in obesity were to continue on the same track, researchers recently predicted that by 2020 almost half of US adults would meet the World Health Organization criteria for obesity.⁷ Compared with the previous 10-year period, the latest NHANES data suggest that the steady upward trend in overweight and obesity may have slowed.³ Even though this finding is certainly good news, the statistics are still staggering—most Americans are overweight and a third are obese—a sobering situation, given the wide variety of deleterious health effects strongly linked to excess weight. These include increased risk of coronary heart disease, ischemic stroke, hypertension, dyslipidemia, type 2 diabetes, joint disease, cancer, sleep apnea, asthma, and a host of other chronic conditions.

Analyses from a national survey of almost 10 000 US adults suggest that obesity is associated with more chronic disorders and poorer health-related quality of life than smoking or problem drinking.⁸ If left unchecked, overweight and obesity have the potential to rival smoking as a public health problem, potentially reversing the net benefit that declining smoking rates have had on the US population over the last 50 years.⁷ Excess weight carries not only an enormous personal burden but an economic one as well. Medical spending for obesity-related conditions accounted for an estimated 10% of total annual US medical expenses in 2008, or $147 billion, according to the Centers for Disease Control and Prevention (CDC).⁹

These adverse lifestyle habits apparently have been passed on to the next generations. The prevalence of overweight and obesity in children and adolescents has increased in parallel with that in adults, and obese children often become obese adults. Based on the 2007-2008 NHANES data, the report by Ogden et al⁴ indicates that almost 17% of school-aged children and adolescents are obese, defined as BMI for age at or above the previously established 95th percentile, and almost 32% are categorized as at or above the 85th percentile of BMI for age, the lowest CDC cut point. It appears that the prevalence of high BMI among children and adolescents reached a plateau between 1999 and 2006. However, 1 group, the very heaviest boys (≥97th percentile) aged 6 through 19 years, has not followed this trend but rather seems to be getting heavier over time.

Early obesity strongly predicts later cardiovascular disease, and excess weight may explain the dramatic increase in type 2 diabetes, a major risk factor for cardiovascular disease. A large Swedish study found that being overweight in late adolescence was comparable with light smoking (fewer than 11 cigarettes per day) in increasing the risk of premature death.¹⁰ In that study population, being obese in late adolescence was as hazardous as heavy smoking in increasing the risk of dying over a 38-year period. Efforts such as revamping school lunches to be healthier and ensuring daily physical activity as part of the school curriculum are under way in some areas, but much more needs to be done to stem the tide of childhood obesity.

Even the developing world is seeing dramatic increases in obesity in children as well as adults. Many countries may experience the obesity “epidemic” the United States currently faces earlier in their epidemiologic transitions. For instance, more than 20% of Chinese children between the ages of 7 and 17 years living in large cities are now overweight,¹¹ and 1 in 5 Chinese adults is overweight or obese.¹² Other data indicate that as many as 60% of South African women may be overweight or obese.¹³

Unlike cigarette smoking, hypertension, and dyslipidemia, there is little consensus on the ideal approach to weight management. Numerous safe and effective therapies are available to lower blood pressure and cholesterol levels, and various over-the-counter products as well as prescription-only medication can be used for smoking cessation. These interventions have contributed to the decline in rates of cardiovascular disease events. In contrast, no large-scale, longer-term trials have demonstrated reduction in clinical events through any weight management strategy. Recent clinical trials suggest that pharmacotherapy and bariatric surgery may hold some promise in promoting weight loss, but long-term success and long-term risks as well as cost-effectiveness have not been fully evaluated.¹⁴ Thus, the centerpiece of weight management is lifestyle changes; however, promoting lifestyle changes to encourage weight reduction has been disappointing.

Although 25% of US men and 43% of US women may attempt to lose weight in any given year, failure rates are exceedingly high. Effective treatment strategies generally involve a multifaceted approach, including dietary counseling, behavioral modification, increased physical activity, and psychosocial support that promotes long-term changes rather than fad diets that offer short-term weight reduction, only to return the individuals to their previous habits after the short-term goal is achieved.

The reports by Flegal et al³ and Ogden et al⁴ in this issue of JAMA offer a glimmer of hope that in the United States at least, the steady, decades-long increases in overweight and obesity may have slowed or perhaps reached a plateau. But even if these trends can be maintained, 68% of US adults are overweight or obese, and almost 32% of school-aged US children and adolescents are at or above the 85th percentile of BMI for age. Given the risk of obesity-related major health problems, a massive public health campaign to raise awareness about the effects of overweight and obesity is necessary. Such campaigns have been successful in communicating the dangers of smoking, hypertension, and dyslipidemia; educating physicians, other clinicians, and the public has yielded significant returns. Major research initiatives are needed to identify better management and treatment options. The longer the delay in taking aggressive action, the higher the likelihood that the significant progress achieved in decreasing chronic disease rates during the last 40 years will be negated, possibly even with a decrease in life expectancy.