6.4: Life Expectancy and Leading Causes of Death
One of the metrics used by epidemiologists to measure the overall health of a population is the average life expectancy. Life expectancy is simply how many years on average a person could expect to live at a given age. If a person was born in this year, how many years would it be expected that they would live? What if they are already 20 years old, or 45, or 65? This life expectancy changes over time depending on which diseases or conditions are the leading causes of death and what age group they tend to affect the most. We can compare life expectancy over decades and determine if we are moving toward longer average lifespans for the population of a specific country or region. We can also compare the life expectancy across different populations - such as gender, race, socioeconomic status, or geographical area etc. in order to identify health disparities that affect people of these different groups. This might help us identify the causes of those disparities, in order to come up with preventative measures that could extend the lifespan for everyone.
The most common diseases leading to death have changed over the last century. In the early 1900s the leading causes of death were infectious diseases like pneumonia, influenza, tuberculosis, and diarrheal diseases, with heart disease (a chronic disease) coming in at the 4th leading cause of death. Infectious diseases are spread between people and can cause death at any age, although the very young (under 5 years old) and older adults tend to be the most at risk. By 1940, this trend had shifted, putting heart disease and cancers at the top and infectious diseases further down - with pneumonia, influenza at #5 and tuberculosis at #7. In 2017, heart diseases, cancers, unintentional injuries (accidents), and chronic lower respiratory diseases were the top 4 leading causes of death. Chronic, noncommunicable diseases like heart disease, diabetes, cancers and COPD are not spread between people (you can’t catch this type of disease like a cold), and they tend to progress over a long period of time - even several decades - which also means that increasing age is a risk factor. Another key feature of chronic diseases is that there are often lifestyle behaviors like nutrition, physical activity, and smoking and environmental factors like exposure to toxins that contribute to their development. Although both chronic diseases and infectious diseases have been leading causes of death over the last century, chronic diseases have certainly begun to outpace infectious diseases up until the COVID-19 pandemic (PPI, 2016).
Average life expectancy takes into account all deaths - those at young ages, middle ages and advanced ages. Chronic diseases will be more likely a cause of death at advanced ages, since these diseases take a long time to develop and cause harm. In the early 1900s, the average life expectancy was around 47 years, but that average was likely skewed due to the high infant and child mortality rates experienced from infectious diseases like tuberculosis and pneumonia. Advances in nutrition, urban sanitation, vaccine and antibiotic development from the 30s to the 60s significantly changed the life expectancy of children and infants, thus also pushing the average life expectancy upward (PPI, 2016).
In 2021, the average life expectancy for all U.S. citizens was 76.4 years, which is a decline from 2020 (77 years) (Arias et al., 2023) and 2019 (78.8) (Arias, Ph.D & Xu, M.D., 2022). The major event causing this shift in average life expectancy was the COVID-19 pandemic, which was a major cause or contributed to 385,676 deaths in 2020 and 463,276 deaths in 2021 ( NVSS - Provisional Death Counts for COVID-19 , 2023). This made COVID-19 the third leading cause of death for both of those years ( FastStats , 2023).
In 2023, COVID-19 deaths dropped to the #10 leading cause of death. For many years heart disease and cancers have been the #1 and #2 leading causes of death for Americans. The list of top 10 causes of death as of 2023 is below, along with a chart in Figure 6.3 based on provisional mortality data from the NVSS.