Fifth Phase of the Epidemiologic Transition

Abstract

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. 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 in this issue of JAMA. The first stage, which dominated most of human history, was characterized by pestilence and famine, when infectious diseaseandmalnutritionkeptaverage life expectancyat about 30 years. In the second stage, occurring in the late 19th and early 20th centuries in the United States and Europe, industrializationandurbanizationledto increasingwealthandacorresponding 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 combinedwithbetternutritiondrovedowndeaths frominfectious diseaseandmalnutrition, leading todeclining infantandchild mortalityandan increased lifeexpectancy.The thirdstage,degenerativeandhuman-madediseases,characterizedbyincreasingmortality fromcardiovasculardiseaseandcancer, emerged in the mid 20th century. Smoking, decreased activity levels in theworkplaceandathome,andincreasedintakeofanimalproductsandfatsresultedinincreasingprevalenceofelevatedblood 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. 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 “preobesity” (BMI between 25.0 and 29.9), and 13.4% were obese. The latest prevalence and trends in obesity data from the National Health and Nutrition Examination Survey (NHANES), reported by Flegal and colleagues 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 inobesitywere tocontinueonthesametrack, researchers recently predicted that by 2020 almost half of US adults would meet the World Health Organization criteria for obesity. Compared with the previous 10-year period, the latestNHANESdatasuggest that thesteadyupwardtrendinoverweight and obesity may have slowed. Even though this finding is certainly good news, the statistics are still staggering— mostAmericansareoverweightandathirdareobese—asobering 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 andpoorerhealth-relatedqualityof life thansmokingorproblem drinking. 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. Excess weight carries not only an enormous personal burden but an economiconeaswell.Medicalspendingforobesity-relatedconditionsaccountedforanestimated10%oftotalannualUSmedi-