Cancer is overtaking heart disease as the leading cause of death in the U.S., particularly in high-income counties, suggests a new analysis published in the Annals of Internal Medicine.
This shift has been forecast for some time, wrote Stanford University researchers led by Katherine G. Hastings, MPH. Cancer mortality exceeded heart disease mortality in only two states in 2000 but in 22 states in 2014, and the CDC has since projected that cancer would be the No. 1 cause of death nationwide by 2020.
To understand these trends at the socioeconomic level, Hastings and colleagues analyzed U.S. death records from 2003 to 2015, with individuals categorized by race/ethnicity and county-level median household income.
The researchers separately calculated age-standardized death rates per 100,000 residents for both cancer and heart disease on an annual basis. They found heart disease was the leading cause of death in 79 percent of U.S. counties in 2003 and 59 percent of counties in 2015. Meanwhile, the counties with cancer as the top cause of death increased from 21 percent to 41 percent over that time frame.
Both causes of death actually declined during the study period, but cancer mortality dropped slower than heart disease (16 percent decline versus 28 percent). Wealthier counties saw greater mortality declines for both conditions compared to low-income counties—30 percent versus 22 percent for heart disease and 18 percent versus 11 percent for cancer.
In general, groups with more socioeconomic advantages demonstrated an earlier shift to cancer as the leading cause of mortality.
“We show transitions occurring earlier in high- versus low-income U.S. counties and earlier for Asian Americans, Hispanics, and (whites) than for blacks and American Indians/Alaska Natives,” the authors wrote. “Our analyses suggest that this shift may arise from larger reductions in heart disease mortality than cancer mortality over time, particularly in high-income counties. However, the transition is complex because of the large overlap in risk factors for these chronic diseases, and it may also be explained by socioeconomic, geographic, demographic, and political factors.”
Other takeaways from the study include:
- The South, compared to other regions, had more counties with higher rates of heart disease mortality than cancer mortality.
- Blacks had the highest overall mortality of any racial group, but also made the greatest improvements from 2003 to 2015. “Our results reiterate the importance of continued efforts to bridge the health gaps among our diverse populations,” Hastings et al. wrote.
- American Indians/Alaska Natives were the only group with higher all-cause mortality from 2003 to 2015 across all income quintiles.
- The median age for heart disease death was 81 throughout the study period compared to 73 for cancer in 2003 and 72 for cancer in 2015.
- Greater proportions of college graduates and higher local government spending were correlated with longer life expectancy at the county level.
“Our findings may provide important insights into the role of geography and socioeconomic status in the continually evolving era of chronic disease mortality,” the researchers noted. “An important extension of this work will be to examine risk factor data (such as smoking, diet, and physical activity levels) using national databases to evaluate how current policies and public health interventions are directly influencing the transition from heart disease to cancer as the leading cause of death.”
The analysis relied on counties’ median household income levels as a proxy for socioeconomic status, rather than data from individuals. The authors also didn’t adjust for cost-of-living by geographic area, which they acknowledged “may also be an important factor when considering income.”
In an accompanying editorial, two Swiss researchers said evolving treatments and tests could further contribute to mortality gaps and must be monitored going forward.
“Novel and expensive cancer therapies are being introduced, and if they are effective, they might contribute in the near future to increasing social inequalities in cancer survival, with better-off persons having more rapid decreases in mortality,” wrote Silvia Stringhini, PhD, and Idris Guessous, MD, PhD, both with Lausanne University Hospital and Geneva University Hospital.
“Social disparities also exist in genetic testing and cancer screening, and this may also contribute to future trends in social inequalities in cancer mortality. … Further research examining the socioeconomic and demographic correlates of these new facets of the epidemiologic transition will help to refine mortality projections in the United States and around the globe.”