Christina M. Shay, PhD, FAHA, Director, Impact and Health Metrics, American Heart Association
In the past 100 years, Americans have gained approximately 25 more years of expectancy. These gains were due to significant declines in mortality that occurred as acute infectious diseases were replaced by chronic diseases as the predominant cause of morbidity and mortality. However, 2017 was the third year in a row where U.S. life expectancy fell, a rare event that has only occurred three times in the last century. One other three-year decline occurred in 1916, 1917 and 1918, when the worst flu pandemic in modern history eliminated nearly 7% of the US population. While this is a worrisome headline, let’s look at what we know and do not know yet from this recent report.
The annual report “Mortality in the United States, 2017” released by the CDC’s National Center for Health Statistics provided several important high-level updates to mortality-related statistics observed in the US between 2016 and 2017, including changes in life expectancy, mortality, and leading causes of death. However, this report is released prior to the release of complete US mortality data from 2017, which will allow a more comprehensive look at the main drivers of these changes. Here are a few highlights from the report (with a bit of interpretation) and a nod towards some still unanswered questions:
- Life expectancy at birth in 2017 (which is the average number of years a baby born at that time is expected to live) declined by approximately 1.2 months between 2016 and 2017. This is a similar decline in life expectancy observed between 2014, 2015 and 2016. Note: When discussing life expectancy, we often are referring to life expectancy at birth, which is the life expectancy of a baby born in that year. However, life expectancy is calculated for many different age categories. Based on 2017 data, the life expectancy at birth was 78.6, but life expectancy for 65 year-olds was 19.5 years. These groups have that many more years to live from 2017 (on average).
- Declines in life expectancy at birth were largely due to increases in mortality from unintentional injuries, suicide, diabetes, and influenza and pneumonia. Interestingly, unintentional injuries made the largest contribution. This is of interest since drug overdoses are commonly categorized on death certificates as poisoning as the cause of death, which is a form of unintentional injury. A separate CDC report with 2017 data focused on mortality from drug overdoses offered more insight on this issue. Age-adjusted mortality rates of drug overdose deaths increased on average by 10% per year from 1999 through 2006, by 3% per year from 2006 through 2014, and by 16% per year from 2014 through 2017. Life expectancy at age 65 increased by 1.2 months between 2016 and 2017, which may indicate that some factors leading to decreases in life expectancy from birth may not influence mortality that occurs at older ages. That may seem obvious for age-related causes of death (like heart disease) but it is suspected these differences in mortality by age are also partly due to the increasing rates of mortality from certain causes in younger age groups such as drug overdoses (i.e. unintentional injuries), which are more likely to impact younger adult/teenage populations. The CDC mortality report focused on drug overdoses confirmed this theory as mortality rates from drug overdoses continued to increase again in 2017 with the highest increases in adults ages 25-64 years.
- Increases in life expectancy in older adults is a favorable sign for the American Heart/American Stroke Association since these improvements may be due to declines in mortality from major cardiovascular-related causes, such as ischemic heart disease and stroke.
- The overall age-adjusted mortality rate increased between 2016 and 2017. This measure is an estimate of the number of deaths from all causes after accounting for: 1) changes in the total number of people, and 2) changes in the number of people by age group in the US population. If we were to only look at the total number of deaths, rather than an age-adjusted death rate, we would not know how much of the increases in the number of deaths are occurring simply because there are more people in the US or if the number of older adults (that have a higher risk of dying) are increasing. Knowing the total number of deaths is important, but age-adjusted mortality rates give us a picture of the population-level changes in mortality without the influence of these factors. The complete mortality data are needed to look more closely at the actual number of deaths by specific cause to determine the causes responsible for the greatest numbers of deaths.
- When looking at the leading causes of death in 2017, mortality rates from heart disease (HD) remained in the #1 position and stroke remained the #5 leading cause from the previous year. Mortality rates for HD decreased (-.5 deaths per 100,000) but mortality rates for stroke increased (+.3 deaths per 100,000). Since the late 1960s, very large declines in heart disease and stroke mortality rates occurred. In more recent years, these declines have greatly slowed or even slightly increased. These plateaus are likely due to the increasing rates of obesity in the US population, which have led to greater rates of diabetes, high blood pressure, and high cholesterol in the US population, which are all major risk factors for heart disease and stroke. It is important to note, the number of years lived with these risk factors further increases risk for heart disease and stroke. Since growing childhood obesity rates in the US are leading to earlier ages of onset for major cardiovascular disease risk factors, there is a concern that mortality rates for heart disease and stroke will more strongly begin to rise as today’s youth/young adults get to ages where heart attacks and strokes are likely to occur. The plateau we are observing in heart disease and stroke mortality may be the first sign of an upcoming trend.
The CDC’s National Center for Health Statistics collects, analyzes and reports data from all death certificated in the US, which is a tall and important public health responsibility. Since there is no national surveillance system for cardiovascular diseases, our best indication of the burden of heart disease and stroke in the US is based on death certificate data. The mortality information presented in this report is just the tip of the iceberg in regards to the extensive information made available when the complete 2017 mortality data are released in December. For more information about detailed mortality data in the US, or other types of health and vital statistics in the US, please visit the CDC WONDER website at https://wonder.cdc.gov/.