Trends in Mortality Among Females in the United States, 1900–2010: Progress and Challenges

Robert A. Hahn, PhD, MPH; Man-Huei Chang, MPH; R. Gibson Parrish, MD; Steven M. Teutsch, MD, MPH; Wanda K. Jones, DrPH

Disclosures

Prev Chronic Dis. 2018;15(3):e30 

In This Article

Discussion

During the past 110 years, mortality rates among females in the United States decreased substantially, particularly for younger females and nonwhite females. Mortality rates from infectious diseases decreased precipitously by mid-century. In contrast, heart disease mortality rates among females increased in the first half of the century; they then decreased during the second half. Mortality from respiratory system cancers and chronic respiratory disease among females also rose dramatically, starting in the mid-1960s. The early risk in UI-MV mortality quickly plateaued and then decreased.

Providing explanations for observed trends is challenging (Appendix III). Available data allow only ecological and retrospective analyses. Sources vary in accuracy, specificity, and consistency over time. Exposures commonly interact, but information on conjoint exposures is lacking. Racial categories and disease categories changed during the study period. Explanations are thus hypothetical and imprecise.

We divided potential explanations into social and environmental factors, such as education, employment, poverty, sanitation, housing, and transportation; biological and behavioral factors, such as hypertension, cholesterol levels, cigarette smoking, physical activity, and diet; and preventive and therapeutic interventions, such as measles vaccination, hypertension screening, and treatment of cardiovascular disease. Changes in ICD coding may also account for some trends observed. Overall, social and environmental explanations and biological and behavioral explanations predominate in the first half of the 20th century, whereas preventive and therapeutic interventions then gained importance.

Twenty years of the 30-year increase in female life expectancy from 1900 to 2010 occurred between 1900 and 1950,[1] affected principally by social and environmental factors. During the first half of the 20th century, sanitation improved substantially, with greater benefits for blacks than for whites.[5,6] Sanitation, the provision of clean drinking water and safe disposal of sewage and solid waste, affected rates of infectious and chronic diseases[6] and was associated with almost half the total decrease in mortality rates in major US cities between 1900 and 1940, three-quarters of the decrease in infant mortality rates, and almost two-thirds of the decrease in child mortality rates.[5]

Decreases in infectious disease mortality rates were also probably associated with improved housing, increased education and income, and reduced poverty.[7] From 1900 to 1940 the mean number of occupants per housing unit in the United States fell from 4.8 to 3.8, reducing infectious disease contagion.[8] The large decrease in major infectious diseases preceded deployment of antibiotics and immunization.

Education, an established determinant of health, increased substantially during this period. From 1900 to 1950, female high school graduation rates increased from almost 30% to approximately 80%.[9] Postsecondary education for females also increased.[10] Between 1940 and 1970, the median years of schooling increased for nonwhite and white females.[8]

There were increases in proportions of the workforce that was female, of married females working outside the home, of female compared with male earnings, and of black compared with white earnings,[10] all contributing to improved economic well-being for females and nonwhites and likely to have led to improved health.

Three major nonexclusive explanations for increased heart disease mortality rates are possible. First, as understanding of diseases improved, the apparent rise may have partly resulted from changes in classifying and assigning causes of death during the first half of the century. Examples include the shift from nonspecific causes, (eg, "ill-defined conditions") to specific causes (eg, ischemic heart disease) and the 1929 reclassification of diseases of the coronary arteries from "diseases of the arteries" to a new subcategory of heart disease, "diseases of the coronary arteries and angina pectoris".[11,12] Second, the rise has also been attributed to a reduction in "competing causes" of death, most notably the reduction of deaths due to infectious and diarrheal diseases.[13]

Third, cigarette smoking was a major influence on trends in female chronic disease mortality rates, particularly trends for heart disease, respiratory system cancers, and chronic lower respiratory disease.[14–16] The prevalence of cigarette smoking among females rose rapidly in the 1930s, peaked from about 1965 to 1975, and decreased thereafter.[15–18] This trend is consistent with the rise of cancer death rates among females in the 1960s. Smoking is also associated with particularly high relative risks for heart disease and stroke among females younger than 50.[15,16] It is plausible that the rapid rise of smoking in the first half of the century was also associated with much mortality, principally from heart disease.[19] Holford et al estimated that the decrease of smoking among females between 1964 and 2012 averted 2.7 million deaths from all causes.[19] However, the decrease in deaths predated the decrease in smoking among females by 5 to 10 years, suggesting that other factors contributed.[13,20] Investigators have called for additional research to explain the 20th century rise and decrease of heart disease.[13,20]

Other causes of heart disease and of stroke merit assessment. Estimates of blood pressure trends indicate that blood pressures decreased during the 20th century,[21] which is consistent with the decrease of stroke mortality rates during the study period. Nationally representative estimates of rates of hypertension in 1960 were 26.4% among white females and 43.1% among black females.[22] Between 1988 and 1991, rates had fallen to 16.7% and 28.1%, respectively.[22] Control of hypertension has increased.[23] Trends in hypertension control are consistent with the accelerating decrease in trends in stroke deaths after 1970.

Nationally, the mean number of kilocalories consumed (ie, acquired but not necessarily ingested) per capita per day (for males and females combined) increased from approximately 3,400 from 1909 to 1919 to 3,900 in 2000.[24] Nationally representative estimates of rates of elevated cholesterol blood levels — another risk factor for heart disease — are not available before 1960, after which mean levels among both black and white females slowly decreased.[25] Criteria for overweight have also changed since 1960, but trends indicate a substantial rise for both black and white females.[26] The prevalence of diabetes in the population — another risk factor for heart disease — rose from 1% in 1958 to 7% in 2011 (data not available for females alone).[27] During the 20th century, total physical activity decreased — a protective factor for heart disease and stroke.[28] Long-term trends in overweight, physical activity, and the prevalence of diabetes do not explain the trends in heart disease and stroke without considering the effects of improved medical care.[26–28] The decrease in saturated fat ingestion is consistent with declining heart disease and stroke mortality rates in the second half of the 20th century.[25]

In the last half of the 20th century clinical interventions were developed and deployed for the treatment of heart disease and stroke.[29] Ford and colleagues estimated that 47% of the decrease in heart disease mortality rates since 1980 are attributable to clinical treatments and 44% to changes in risk factor prevalence.[30] Conversely, increases in the prevalence of overweight and diabetes may have slowed the rate of decrease in heart disease mortality rates. Various screening tests (eg, mammography, Pap tests, colonoscopy) also affect mortality associated with specific cancers. Their use in the second half of the 20th century, along with advances in treatment, may be responsible for some of the decrease of age-adjusted cancer mortality rates.[31]

Since 1998, the anomalous increasing death rate among white females in certain age groups has been noted, particularly among those with a high school education or less. Deaths are largely attributed to drug and alcohol poisoning, suicide, chronic liver disease, and cirrhosis.[32] We found that these increases began earlier than previously reported and affected additional age groups.

The lack of large increases in UI-MV deaths during the 20th century is notable.[33] From 1900 to 1970, the number of automobiles rose from 4,100 to 6.5 million; from 1923 to 1970, the miles of federally supported highways grew five fold; miles driven per capita annually climbed almost six fold from 1930 to 2000; and from 1945 to 1970, average vehicle highway speed increased from 45 to 60 miles per hour.[8] Large increased exposure to risks for UI-MV deaths, is not, however, reflected in long-term trends in UI-MV mortality rates. Deaths per mile driven reached a low peak in 1930 and gradually decreased thereafter, probably in association with safety measures.[34] In the first 3 decades of the 20th century, many UI-NMV deaths were from falls, drowning, railroad injuries, and burns;[2] these causes decreased greatly after 1940. However, in recent decades deaths among females from drug overdoses have risen rapidly and since 2007 have exceeded deaths from UI-MV.

Much of the decrease in mortality rates among females in the past 110 years is attributable to improvements in major social and environmental determinants of health — education, income, housing, and sanitation. The rapid decrease in mortality rates from infectious by mid-century largely preceded the widespread use of antibiotics or immunization. The extent and specific causes of increased heart disease mortality rates among females in the first half of the century remain uncertain. The decrease of heart disease mortality rates during the second half of the century may be the result of multiple factors. The dramatic rise in mortality rates from respiratory system cancers and chronic respiratory disease among females is most likely due to cigarette smoking. The plateau in UI-MV mortality rates, despite the rapid growth of automobile use during the century, is probably a result of early safety measures.

Trends in mortality rates during the past century reflect major patterns of health determinants. Sanitary and safety improvements along with understanding of and therapies for infectious diseases led to great reductions in infectious causes of death. With increasing longevity and more sedentary lifestyles, chronic diseases increased as major causes of death. Although some of these causes, particularly heart disease and stroke, decreased as a result of behavior change and effective health care,[22] decreases in mortality rates are slowing. Ongoing and expanded efforts to control underlying determinants should accelerate decreases in mortality rates and reduce inequities.

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