Disease and Conditions

Measures of Human Disease and Condition

The term “cancer” refers to diseases in which abnormal cells divide without control, losing their ability to regulate their own growth, control cell division, and communicate with other cells. Cancer is the second leading cause of death in the United States (General Mortality indicator). More than one in three people in the United States will develop cancer and nearly one in four will die of it.¹

In response, scientists continue to explore the role that the exposure to environmental contaminants may play, along with other possible risk factors, in the initiation and development of cancer. Some environmental contaminant exposures are known risk factors for certain types of cancers. Examples include radon and lung cancer and arsenic and skin cancer.

Though many types of cancer are suspected of being related to ambient environmental exposures, associations are not always clear because the etiology of cancer is complex and influenced by a wide range of factors. Many factors can increase individual cancer risk, such as age, genetics, exposure to certain infectious diseases, and socioeconomic factors that can influence exposure and susceptibility.

Childhood cancers are dissimilar from cancers in adults and are therefore tracked separately. They affect different parts of the body and may be of embryonic origin. Though overall cancer incidence rates are lower in children than in adults, childhood cancers are the leading cause of disease-related death in children age 1 to 19 years.^2,3

Children may be particularly susceptible to exposures in utero or during early childhood because their bodies are rapidly developing and affected by changing hormone levels.⁴ As with many adult cancers, the causes of childhood cancers are unknown for the most part; environmental influences may be a factor and have been the subject of extensive research. Environmental exposures are difficult to evaluate because cancer is rare in children and because of challenges in identifying past exposure levels, particularly during potentially important time periods such as in utero or maternal exposures prior to conception.⁵

More than one-third of the U.S. adult population lives with a cardiovascular disease.⁶ Coronary heart disease and stroke, two of the major types of cardiovascular disease, rank as the first and fourth leading causes of death, respectively (General Mortality indicator), and are leading causes of premature and permanent disabilities.

Known risk factors include smoking, high blood pressure, high blood cholesterol, diabetes, physical inactivity, and poor nutrition. Outdoor air pollution and environmental tobacco smoke are also known risk factors for cardiovascular disease. Particulate matter, for example, has been demonstrated to be a likely causal factor in both cardiovascular disease morbidity and mortality.

Collective evidence suggests short-term exposures to particulate matter is associated with excess risk of hospital admissions or emergency department visits for cardiovascular effects.^7,8,9 Environmental tobacco (secondhand) smoke has been shown to be a risk factor for morbidity and mortality from coronary heart disease and possibly stroke.^10,11

Chronic obstructive pulmonary disease (COPD) and asthma are two prevalent chronic respiratory diseases. Chronic lower respiratory diseases represent the third leading cause of death in the United States (General Mortality indicator).

Epidemiological and clinical studies have shown that ambient and indoor air pollution are risk factors for several respiratory health outcomes, including reported respiratory symptoms (nose and throat irritation), acute onset or exacerbation of existing respiratory diseases (e.g., asthma), and deaths.^12,13,14

The relationship between environmental tobacco smoke and diseases of the respiratory tract has been studied extensively in humans and in animals; environmental tobacco (secondhand) smoke has been shown to produce a variety of upper and lower respiratory tract disorders, in adults and children.^15,16

COPD is a group of diseases characterized by airflow obstruction, resulting in breathing-related symptoms; it encompasses chronic obstructive bronchitis and emphysema.¹⁷ COPD is a leading cause of death and hospitalizations, particularly among older adults. It represents a major cause of morbidity, mortality, and disability.¹⁸ Although a large percentage of COPD deaths is attributed to smoking, air pollution and environmental tobacco (second-hand) smoke may be important contributors to COPD.¹⁹

Asthma continues to receive attention in both children and adults. Asthma prevalence grew nearly 74 percent during 1980–1996, and has held steady with more than 20 million people in the United States still reporting asthma each year.^20,21 Environmental exposures such as outdoor air pollution (e.g., particulate matter, ozone), environmental tobacco smoke, dust mites, pets, mold, and other allergens are considered important triggers for asthma.^22,23,24

Infectious diseases are acute illnesses caused by bacteria, protozoa, fungi, and viruses. Food and water contaminated with pathogenic microorganisms are the major environmental sources of gastrointestinal illness. Though well-established systems for reporting food- and waterborne cases exist, data reported through these largely voluntary programs must be interpreted with caution, because many factors can influence whether an infectious disease is recognized, investigated, and reported.

Changes in the number of cases reported could reflect actual changes in disease prevalence or simply changes in surveillance and reporting. In addition, many milder cases of gastrointestinal illnesses are not diagnosed or go unreported, making it difficult to estimate the number of people affected every year.

The discovery of bacterial contamination of drinking water as the cause of many cases of gastrointestinal illness represents one of the great public health success stories of the 20^th century.

Waterborne diseases such as typhoid fever and cholera were major health threats across the United States at the beginning of the 20^th century. Deaths due to diarrhea-like illnesses, including typhoid, cholera, and dysentery, represented the third largest cause of death in the nation at that time.

These diarrheal-related deaths dropped dramatically once scientists identified the bacteria responsible, elucidated how these bacteria were transmitted to and among humans in contaminated water supplies, and developed effective water treatment methods to remove pathogens from water supplies.

In addition to being of food- or waterborne origin, infectious disease can be airborne, arthropod-borne (spread by mosquitoes, ticks, fleas, etc.), or zoonotic (spread by rodents, dogs, cats, and other animals). Legionellosis can be contracted from naturally occurring bacteria found in water and spread through poorly maintained artificial water systems (e.g., air conditioning, ventilation systems). Arthropod-borne diseases, including Lyme disease, Rocky Mountain spotted fever, and West Nile virus, can be contracted from certain ticks and mosquitoes that acquire bacteria or viruses by biting infected mammals or birds.

Birth defects are structural or functional anomalies that present at birth or in early childhood. Birth defects cause physical or mental disability and can be fatal. They affect approximately one out of 33 babies born each year in the United States and remain the leading cause of infant mortality (Infant Mortality indicator). People with birth defects may experience serious, adverse effects on health, development, and functional ability.

Birth defects have been linked with a variety of possible risk factors that can affect normal growth and development. These include genetic or chromosomal aberrations, as well as environmental factors such as exposure to chemicals; exposure to viruses and bacteria; and use of certain medications, cigarettes, or alcohol by the mother. The causes of most birth defects are unknown, but research continues to show the possible influence of environmental exposures.²⁵

Low birthweight and preterm delivery are considered important risk factors for infant mortality and birth defects. Low birthweight and preterm infants have a significantly increased risk of infant death, and those who survive are more likely to experience long-term developmental disabilities.^26,27 Multiple birth babies have a low birthweight rate of more than 50 percent, compared to approximately 7 percent among singletons.²⁸ To eliminate the effect that multiple births may have on birth outcomes, the indicators in this report include data for singleton births only.

Environmental exposures are being investigated for possible associations with birth outcomes such as low birthweight, preterm delivery, and infant mortality. Some of the risk factors for low birthweight infants born at term include maternal smoking, weight at conception, and maternal nutrition and weight gain during pregnancy.²⁹

Specific examples of known or suspected environmental contaminant influences on birth outcomes include environmental tobacco (second-hand) smoke, lead, and air pollution. Second-hand smoke is associated with increased risk of low birthweight, preterm delivery, and sudden infant death syndrome.³⁰ Several studies have identified lead exposure as a risk factor for preterm delivery.³¹ Growing evidence shows exposure-response relationships between maternal exposures to air pollutants (e.g., sulfur dioxide and particulates) and low birthweight and preterm delivery.^32,33,34

Research continues, however, in establishing causal relationships between air pollution and low birthweight and preterm birth. Researchers also continue to examine possible associations between other contaminants as birth outcome risk factors, such as pesticides, polycyclic aromatic hydrocarbons, and others.

EPA selected indicators for human diseases and conditions with well-established associations of exposures to environmental contaminants. EPA recognizes that, in most cases, risk factors are multi-factorial, and that the development of a particular disease or condition depends on the magnitude, duration, and timing of the exposure. The diseases and conditions addressed in this ROE question may be associated with, but cannot be tied directly to the contaminant levels or other environmental conditions reported by national-level ROE indicators in Air, Water, and Land.

There are other diseases or conditions of potential interest for which no national-scale data are currently available, or for which the strength of associations with environmental contaminants is still being evaluated. Additional data are needed to enable EPA to track other diseases and conditions with potential environmental risk factors (direct or indirect), particularly those for which unexplained increases are being noted. Examples of diseases or conditions with suggestive or growing evidence that environmental contaminants may be a risk factor include behavioral and neurodevelopmental disorders in children, neurodegenerative disorders, diabetes, reproductive disorders, and renal disease.