Relationship of Lifestyle Risk Factors to Sudden Death
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville.
Source: Chiuve SE, et al. Adherence to a low-risk, healthy lifestyle and risk of sudden cardiac death among women. JAMA 2011;306:62-69.
This paper presents data from the Nurses' Health Study. This is a large study that was begun in 1976 which surveyed nurses with initial ages between 30 and 55 and collected data on lifestyle and other risk factors and correlated these data with the development of cardiac disease. In this study, data from the 1984 survey were used as the baseline for analysis. The study collected data biannually that included smoking status, body weight, use of medications, menopausal status, and physician diagnosis of disease. Physical activity was assessed every 2 to 4 years using a validated questionnaire. Diet was assessed using a validated food frequency questionnaire that was filled out every 4 years. In this paper, the authors considered the relationship of four lifestyle factors: smoking, exercise, diet, and weight to the incidence of sudden cardiac death (SCD). Most of the data presented consider these findings in a binary fashion as either high or low. Low-risk categories included physical activity of 30 minutes per day or longer, a body mass index of 25 or less, an alternate Mediterranean diet score in the top 40% of the cohort distribution, and no current smoking. Mortality data were collected through medical records, autopsy reports, and interviews with next of kin. Cardiac deaths were considered sudden if the death or cardiac arrest occurred within 1 hour of symptom onset and was not associated with evidence of circulatory or neurologic impairment before death. Unwitnessed and unexpected deaths were considered to be sudden deaths.
During 26 years of follow-up, there were 321 cases of SCD. Nonsmokers, those who exercised regularly, and those adhering to a Mediterranean diet had a lower risk of sudden death. The association between BMI was J shaped with a nadir in sudden death risk among women with a BMI of 21 to 24.9. When the four risk factors (smoking, diet, exercise, and weight) were combined as binary values in a lifestyle assessment, the total score was inversely associated with the risk of sudden death. For women with no low-risk factors, the sudden death rate was 22 cases per 100,000 person years. With 1, 2, 3, and 4 low-risk factors, the rates were 17 cases (score 1), 18 cases (score 2), 13 cases (score 3), and 16 cases per 100,000 patient years (score 4). For the individual factors, the relative risk for nonsmoking was 0.5, for frequent exercise was 0.62, for the Mediterranean diet was 0.69, and for BMI less than 25 was 0.8. In the entire cohort, the percentage of population attributable risk for sudden death associated with these four lifestyle factors was 81%.
The authors acknowledge that their data can be strictly applied only to highly educated white female health professionals and may not be generalizable to men or women of other ethnicities or socioeconomic status. However, identifying these lifestyle factors provides the basis for a sudden death prevention strategy.
This paper identifies four potentially modifiable risk factors for sudden death in middle-aged women. These risk factors also are linked to the development of hypertension and ischemic heart disease and may not be specific for sudden death itself. However, these four factors are modifiable by lifestyle changes and reducing the total heart disease burden attributable to these factors would have a tremendous impact on public heath in general without the need for expensive medications or procedures. The challenge is to translate this knowledge into effective prevention strategies.