ARIC: US stroke incidence, mortality rates declined from 1987 to 2011
The rates of stroke incidence and stroke mortality in the United States declined from 1987 to 2011, according to new data from the Atherosclerosis Risk in Communities study.
The decline was consistent across sex and race, but the decline in incidence was driven by those aged at least 65 years and the decline in mortality was driven by those younger than 65 years, according to the researchers.
“More successful control of risk factors in the last decades (mainly hypertension control starting in the 1970s and later hypertension treatment combined with smoking cessation, control of diabetes and dyslipidemia, and treatment of atrial fibrillation) may have resulted in lower stroke incidence and less severe strokes, which may account for the observed lower mortality rates,” Silvia Koton, PhD, MOccH, and colleagues wrote.
The Atherosclerosis Risk in Communities (ARIC) study was a prospective cohort study of 14,357 participants aged 45 to 64 years and free of stroke at baseline recruited from four US communities. Baseline interviews and examinations were conducted between 1987 and 1989, and researchers identified stroke hospitalizations and deaths for participants through 2011.
Koton, of the Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, and colleagues found that 7% of participants had incident stroke during the study period. Of the 1,051 participants who had a stroke, 929 had ischemic stroke and 140 had hemorrhagic stroke (18 had both).
Incidence decreased over time
According to the researchers, crude incidence rates were as follows: 3.73 (95% CI, 3.51-3.96) per 1,000 person-years for total stroke, 3.29 (95% CI, 3.08-3.5) per 1,000 person-years for ischemic stroke and 0.49 (95% CI, 0.41-0.57) per 1,000 person years for hemorrhagic stroke.
They found that stroke incidence decreased over time in white and black participants (age-adjusted incidence rate ratios per 10-year period, 0.76; 95% CI, 0.66-0.87; absolute decrease, 0.93 per 1,000 person-years overall).
The decrease in age-adjusted incidence was evident for those aged 65 years and older (age-adjusted incidence rate ratios per 10-year period, 0.69; 95% CI, 0.59-0.81; absolute decrease, 1.35 per 1,000 person-years) but not for those younger than 65 years (age-adjusted incidence rate ratios per 10-year period, 0.97; 95% CI, 0.76-1.25; absolute decrease, 0.09 per 1,000 person-years; P for interaction=.02), Koton and colleagues found. There was no difference by sex in the decrease.
Of those who had incident stroke, 58% had died by 2011, with the mortality rate being higher for hemorrhagic stroke than for ischemic stroke (68% vs. 57%), the researchers found.
Overall mortality after stroke decreased over time (HR=0.8; 95% CI, 0.66-0.98); absolute decrease, 8.09 per 100 strokes after 10 years per 10-year period), according to the researchers.
They found that the decrease in mortality was mainly attributable to those younger than 65 years (HR=0.65; 95% CI, 0.46-0.93; absolute decrease, 14.19 per 100 strokes after 10 years per 10-year period) and was consistent across race and sex.
Risk factors better controlled
Ralph L. Sacco
The study permits comparisons of time-varying vascular risk factors that can help explain reasons for the decline in stroke incidence in mortality, Ralph L. Sacco, MD, and Chuanhui Dong, MD, PhD, both from the department of neurology at the Miller School of Medicine, University of Miami, wrote in a related editorial.
First, they wrote, those who were aged 55 to 64 years between 1996 and 1998 were more likely to use cholesterol-lowering medications compared with those who were aged 55 to 64 years between 1987 and 1989 (12.9% vs. 3.8%) and had an average of 20 mg/dL lower LDL; this is important because of an association between cholesterol medication use and lower rate of incident stroke (RR=0.8; 95% CI, 0.68-0.93).
Second, participants were more likely to use antihypertensive medications between 1996 and 1998 compared with between 1987 and 1989 (43.4% vs. 29.5%), and the increase was mainly seen in those aged 65 years and older, which could explain the higher rate of decline in stroke incidence among older patients, Sacco and Dong wrote.
Third, participants were less likely to smoke between 1996 and 1998 than they were in 1987 to 1989, Sacco and Dong wrote. “Successes in the control of cholesterol levels, [BP] and smoking habits over the last decades are likely partially responsible for the decline in stroke incidence,” they stated.
However, they noted, “formidable challenges to address stroke disparities and successfully control risk factors and lifestyle behaviors across race, ethnicity and regions persist.”
For more information:
Disclosure: The study was funded by the NHLBI. The researchers, Dong and Sacco report no relevant financial disclosures.