To provide examples of different approaches to preventing illness, we have chosen to discuss two serious health problems in the United States: coronary heart disease and breast cancer.
Coronary heart disease (CHD) is associated with four major risk factors: the eating of an unhealthful diet, elevated levels of serum cholesterol, cigarette smoking, and hypertension (Stamler, 1992a).
Primary prevention strategies are available for CHD because the causes of the disease are well understood. Primary CHD prevention involves risk factor reduction, including cessation of cigarette smoking, replacement of highly processed foods with fruits, vegetables, and whole foods, and control of hypertension. These strategies have been largely responsible for the large decrease in CHD death rates (Fig. 11-2).
Trends in age-adjusted mortality from coronary heart disease in the United States, 1980–2010. (Source: US Department of Health and Human Services. Health United States. 2013.)
Tobacco has been called the smallpox virus of chronic disease—a harmful agent whose elimination from the planet would benefit humankind (Fee & Krieger, 1993). Since the 1964 release of the first Surgeon General’s Report on the Health Consequences of Smoking, the smoking behavior of the US population has changed dramatically. Between 1965 and 2012, the age-adjusted percentage of adult men who were current smokers dropped from 51 to 21%; for adult women, the decline was from 34% to 16% (Fig. 11-3). These reductions in smoking prevalence avoided an estimated 3 million deaths between 1964 and 2000—a major public health achievement (Warner, 1989). However, rates of smoking are far higher among people with low educational levels and low income, e-cigarette use is increasing, and smoking continues to be the leading cause of death in the United States (US Department of Health and Human Services, 2013).
Cigarette smoking by persons 18 years and older in the United States in 1965 (light blue bars) and 2012 (dark blue bars). Percentages are age adjusted. (US Department of Health and Human Services. Health United States. 2013.)
Antismoking campaigns have been relatively successful for well-educated people, but less so for people with less education, who also tend to be poorer. Between 1974 and 2012, cigarette smoking declined 40% among the least educated persons, while it dropped 71% among the most educated. In 2012, 26% of the least educated persons smoked cigarettes, compared with only 8% of the most educated (US Department of Health and Human Services, 2013).
Since the 1969 ban on radio and television cigarette advertising, the tobacco industry has increased its advertising expenditures dramatically in the print media and through sponsorship of community events. In 2012, tobacco advertising expenditures exceeded $9 billion, with the principal target group young adults (Centers for Disease Control, 2013). The antismoking campaign of the past 30 years has merged the medical and public health models of prevention. Physician counseling can influence smokers to quit. In 2006, however, only 34% of low-income smokers had smoking cessation discussions with their health care provider (Cokkinides et al., 2009). Public health measures are more effective, including public education, cigarette taxes, and restriction of smoking in public places. A 10% increase in the price of cigarettes reduces cigarette consumption by 3% to 5%. Yet compared with other developed nations, the United States has relatively low taxes on tobacco (Cokkinides et al., 2009; Schroeder & Warner, 2010).
Dietary patterns in the United States are too low in vegetables, fruit, whole grains, and low-fat dairy, and too high in refined grains, saturated fat, added sugars, and sodium. This diet produces CHD in part by causing an increase in low–density-lipoprotein cholesterol. Lowering cholesterol levels reduces the risk of heart attacks caused by CHD.
In the late 1980s, a major national campaign was launched by the National Institutes of Health (NIH) to reduce serum cholesterol levels. This National Cholesterol Education Program is based on the medical model, with health care providers screening individuals for elevated cholesterol and aggressively treating hyperlipidemic patients with diet, cholesterol-lowering medications, or both (Grundy et al., 2004).
Public health analysts have criticized the NIH strategy as relying too heavily on a medical model of prevention that is expensive and of potentially limited effectiveness. The NIH approach targets more than 100 million people who need dietary changes and recommends drug treatment for many of these individuals. The use of statin drugs to treat hyperlipidemia in people with known CHD (secondary prevention) and without CHD (primary prevention) has been shown to reduce deaths from CHD, but the effectiveness of drug treatment is greater if it is used in secondary rather than primary prevention (Hayward et al., 2010).
The NIH cholesterol reduction strategy highlights the paradox of primary prevention: Prevention within a population of healthy individuals is better (and less expensively) served by broad public health efforts to reduce risk among the majority of people at moderate risk than by concentrating intensive medical interventions on the smaller number of high-risk persons (Rose, 1985). The traditional orientation of physicians toward individual patients (the medical model) has led the medical profession and the NIH to emphasize identification and treatment of high-risk individuals with elevated cholesterol levels. Pharmaceutical manufacturers also have an interest in promoting a medical model that relies on prescribing medications.
Currently, public health efforts to curb the consumption of unhealthy foods are failing; 69% of adults in the United States were classified as overweight or obese in 2012, compared with 56% in 1988 (US Department of Health and Human Services, 2013). The food industry spends billions of dollars on advertising, a substantial portion of which promotes high-fat fast foods. Proposals have been made to copy the strategy used by tobacco prevention campaigns in reducing the availability of high-fat foods; for example, taxing unhealthy foods, changing school lunch and food stamp programs to reduce their fat and sugar content, restricting food advertising directed at children, and eliminating school-based candy and soft-drink vending machines are primary preventive measures that are slowly gaining public acceptance (Frieden et al., 2010b; Basu et al., 2014). Attention is also being paid to the billions of dollars annually in federal subsidies to agribusinesses for growing corn, which contributes to the flooding of the nation with low-cost, high-fructose corn sweeteners and other high-calorie processed foods. Public health advocates have called for reforms to the federal farm bill to reduce subsidies for obesogenic foods and to provide more support for sustainable farming of healthful fruits and vegetables (Pollan, 2007; Wallinga, 2010).
Nearly half of deaths from cardiovascular disease (heart attacks and strokes) are attributable to high blood pressure (hypertension), which affects one-third of the US adult population. High sodium intake is a major risk factor for developing hypertension and reducing salt intake is effective in reducing blood pressure (Bibbins-Domingo et al., 2010; Coxson et al., 2013).
Most efforts at hypertension control are based on the medical model, treating individuals with medications. Yet, similar to the cholesterol situation, the greatest impact in reducing hypertension-related mortality rates will come from a reduction in the blood pressure of the large number of borderline hypertensives rather than from focusing solely on people with very high blood pressure (Stamler, 1992b).
Primary prevention of high blood pressure can be accomplished by a reduction in the daily intake of sodium from the current average level of 3,600 mg per day to the recommended level of 1,500 mg per day. Such a change would reduce the number of cardiovascular deaths by 280,000 to 500,000 over 10 years, far more effective than the medical model, The public health approach needed to accomplish this feat would require that food manufacturers be required to reduce sodium in processed and commercially prepared foods by 50% (Coxson et al., 2013), in addition to encouraging people to eat fewer processed foods.
Whereas mortality rates for cardiovascular disease declined since the late 1960s, cancer mortality rates continued to increase through 1990. Between 1990 and 2010, cancer mortality rates dropped by 20%, in part due to reductions in cigarette smoking. Breast cancer mortality rates have also decreased during those years, but are far higher for African American women than for white women (US Department of Health and Human Services, 2013).
The designing of effective primary prevention for a disease generally depends on an understanding of the epidemiology of that disease. In the case of lung cancer, the discovery of the link with cigarette smoking allowed a widespread primary prevention program to be developed. But the causes of many cancers are still unclear, meaning that preventive strategies must use secondary rather than primary prevention. Pap smears for early detection of cervical cancer, fecal occult blood testing and colonoscopy for early detection of colorectal cancer, and mammography for early detection of breast cancer are examples of secondary prevention.
Multiple risk factors for breast cancer have been uncovered, including age greater than 65 years, family history of breast cancer, atypical hyperplasia on breast biopsy, and more years of ovulatory menstrual cycles (American Cancer Society, 2015).
However, only one-third of breast cancer cases can be accounted for by known risk factors. The differences between high and low age-adjusted breast cancer risk in the United States are small compared with the huge differences between such high-incidence nations as the United States and low-incidence (generally underdeveloped) nations. Perhaps unknown agents related to modern industrialization are the primary causes of breast cancer, while such influences as female hormones are secondary promoters of the disease.
The age-adjusted incidence (new cases) of breast cancer fell sharply in 2003 compared with 2002 and continued to fall slightly through 2006, a phenomenon temporally related to the drop in the use of hormone replacement therapy by women in the United States, occasioned by the widely publicized report from the Women’s Health Initiative providing new data on the risks of hormone replacement therapy (Ravdin et al., 2007). This association suggests that estrogen is an important cause or facilitator of breast cancer.
From the 1940s to the 1980s, industrial production of synthetic organic chemicals rose from 1 billion to 400 billion pounds annually, and the volume of hazardous wastes also increased 400-fold during that period (Epstein, 1990, 1994). In 2010, the President’s Cancer Panel reported that “the true burden of environmentally induced cancer has been grossly underestimated.” Studies have linked breast cancer risk to organochlorine insecticides, polycyclic aromatic hydrocarbons, and organic solvents, but research on these environmental causes of breast cancer has been inadequate and inconsistent (Brody & Rudel, 2003). Until the main causes of breast cancer are known, public health has been forced to retreat to secondary prevention to reduce mortality rates in women with the disease. Periodic mammograms can reduce breast cancer mortality rates in women above 50 years of age. Yet many breast cancer activists decry the paltry sums going for basic epidemiologic research to determine the causes of breast cancer.
The examples of CHD and breast cancer illustrate different aspects of illness prevention. Primary prevention has been successful in reducing mortality rates for CHD. Both public health and medical approaches have been used, with far greater emphasis given to the latter strategy. Secondary prevention has had some success in reducing breast cancer mortality rates, but the incidence of the disease remains high and primary prevention is badly needed.