Among the 4549 participants at baseline, 42 participants had a history of stroke. The age- and sex-adjusted prevalence proportion is 1132/100,000. The prevalences for 45–54, 55–64, and 65–74 year-old groups were 450, 1130, 1870/100,000 respectively. Age-adjusted prevalences for men and women were 1625, and 695/100,000 respectively. Age- and sex-adjusted prevalence for Arizona, Oklahoma, and South/North Dakota - 741/100,000 (10 cases, 95% confidence interval: 0–1511.9), 1352 (18 cases, 0–2754.6) and 1193 (14 cases, 0–3091.9) did not differ significantly.
Incidence rate of stroke ()
From 1989 to 2004, 306 incident strokes occurred among the Strong Heart Study participants without a prior stroke, an age- and sex- adjusted incidence of 679/100, 000 person-years. The incidence increased with older age in both men and women in all three centers. The age-adjusted incidences for men and women were 707, and 653/100,000 person years respectively.
Age- and sex-specific incidence rates of stroke per 100,000 person years (1989–2004)
Stroke sub-types ()
Cerebral infarctions were by far the predominant sub-type of stroke, constituting 86% of incident stroke cases; 14% suffered hemorrhagic stroke, mostly intraparenchymal. Intraparenchymal hemorrhages were more common in the youngest age group (45 to 54 years olds).
Proportion of stroke sub-types by age (1989–2004)
Age of occurrence of first stroke
The mean age of occurrence of first stroke for all strokes and for cerebral infarction is 66.5 years. Arizona participants with strokes were younger than Oklahoma participants with strokes (mean ages 65 vs. 68 years respectively, p=0.048). The mean age of Dakota participants with strokes (66.4 years) did not differ from Oklahoma or Arizona. The average age of stroke onset was similar in men (66.2 years) and women (66.7 years) (p=0.60).
Overall 30-day case-fatality from first stroke was 18%, with a one-year case-fatality of 32% (). While the 30-day and one-year case-fatality rates for men and women did not differ, fatality rates were higher in Arizona than the other two centers.
Age-adjusted thirty day- and one-year mortality from first stroke (1989 – 2004)
Characteristics of participants with or without incident stroke ()
Participants with incident stroke were older, had higher systolic and diastolic blood pressures, triglycerides, fasting glucose, hemoglobin A1c, insulin, and two hour glucose, and lower high-density lipoprotein cholesterol levels and were less physically active at baseline than participants who remained stroke-free. Hypertension, diabetes, micro-albuminuria and macro-albuminuria were significantly more prevalent at baseline among participants with subsequent stroke, and those with incident stroke were more likely at baseline to be past alcohol users but less likely to be current alcohol users than those who remained stroke-free.
Comparison of baseline characteristics of the Strong Heart Study participants with and without incident stroke
Risk factors for stroke ( and )
Participants with elevated baseline levels of blood pressure, fasting glucose, HbA1c and albuminuria had significantly higher incidence of stroke than those with normal levels (). Participants with lower levels of HDL-C had significantly higher stroke incidence than those with higher levels. Baseline LDL-C levels were not significantly related to stroke incidence, nor were those of non-HDL-C (data not shown). Current smokers had significantly higher stroke incidence than past smokers and non-smokers as did participants with hypertension, pre -hypertension, diabetes, and impaired glucose compared to those who did not have those conditions.
In a Cox proportional hazard model for all strokes, age, diastolic blood pressure, fasting glucose, smoking, and albuminuria were risk factors of stroke incidence. Current and past smokers had 2.4- and 1.6-fold higher risks of incident stroke, respectively, than never smokers. Macro-albuminuria, and micro-albuminuria increased the risk 3.3 and 1.7 times, respectively. When hypertension and pre-hypertension were put in the model instead of systolic and diastolic blood pressures, the risks of incident stroke were 2.2 and 1.8 times higher than in normotensive participants. When HbA1c was put in the model instead of fasting glucose, each percent increase of HbA1c was associated with a 1.15-fold higher risk of incident stroke. When diabetes and impaired glucose metabolism were put in the model instead of fasting glucose, they increased the risk of incident stroke by 2.1- and 1.2-fold, though the effect of impaired glucose metabolism was not statistically significant. The results of the multivariable model for cerebral infarction only (data not shown) are similar to the results for all strokes. Although insulin levels were associated with incident stroke in univariable analyses, the association was not significant after adjusting for other covariates.
Stroke incidence (per 100,000 person-years) according to different risk factors (age and gender adjusted)
Cox proportional hazards model for all strokes