Prevalence of Aspirin Use to Prevent Heart Disease -- Wisconsin, 1991, and Michigan, 1994

In the late 1980s, a series of secondary prevention trials documented that regular use of aspirin lowered the risk for myocardial infarction (MI) and nonfatal strokes in persons with cardiovascular disease (CVD) (1,2). Subsequently, a large randomized trial demonstrated that regular use of aspirin decreased the risk for MI by approximately half in healthy male physicians with no history of CVD (3), suggesting a potential role for aspirin in primary prevention of heart disease. In 1989, the U.S. Preventive Services Task Force (USPSTF) recommended that regular low-dose aspirin should be considered for men aged greater than or equal to 40 years who were at substantially increased risk for MI and who lacked contraindications to the drug (4). To assess the prevalence of self-reported, regular aspirin use to prevent heart disease among adults aged greater than or equal to 45 years, both the Wisconsin and Michigan state health departments collected information in their Behavioral Risk Factor Surveillance System (BRFSS) surveys (in 1991 and 1994, respectively). This report summarizes the results of these surveys, which indicate that a high proportion of adults in those states used aspirin regularly to prevent heart disease.

The BRFSS is a random-digit-dialed survey of the U.S. civilian, noninstitutionalized population aged greater than 18 years. In 1991, the Wisconsin BRFSS included the question "Do you take aspirin regularly to reduce your chances of having a heart attack?" In 1994, Michigan asked "Do you take aspirin daily or every other day to reduce your chance of a heart attack or stroke?" Responses were obtained from 548 and 1137 adults aged greater than or equal to 45 years in Wisconsin and Michigan, respectively. The overall prevalence of aspirin use was 19.5% in Wisconsin in 1991 and 25.3% in Michigan in 1994. Because univariate results in each state were similar, the data were combined for more detailed analyses using SUDAAN. Statistical associations between explanatory variables and aspirin use were tested using the chi-square test of association. For those variables with an overall statistically significant association with aspirin use (p less than 0.05), pairwise comparisons of age-adjusted prevalence estimates were performed (Table_1). Age-adjusted estimates were calculated using the pooled age distribution from both data sets. A composite risk-score variable also was constructed using a combination of three risk factors -- current smoking, overweight, and inactivity.

The overall prevalence of aspirin use in the combined data was 23.3% (Table_1). Prevalences increased directly with age from 16.0% of persons aged 45-54 years to 22.0%, 28.8% and 33.3% for persons aged 55-64, 65-74, and greater than or equal to 75 years, respectively. Age-adjusted prevalences were higher for men (27.7%) than women (20.1%), current (25.5%) and former smokers (28.8%) than respondents who never smoked (18.0%) (Table_1), and persons who engaged in regular leisure-time physical activity (26.3%) than persons who were inactive (20.8%). There were no statistically significant associations between aspirin use and race, education, income, overweight, or composite risk-score. Prevalences were similar when the analysis was stratified by sex.

Reported by: MJ Reeves, PhD, H McGee, MPH, AP Rafferty, PhD, Michigan Dept of Community Health, Lansing. P Remington, MD, E Cautley, MS, Wisconsin Div of Health and Family Svcs, Madison.

Editorial Note

Editorial Note: Approximately 40% of all deaths in the United States are attributed to CVD, and annual direct and indirect costs of CVD have been estimated to be $259 billion (5). In addition to population-based approaches to reducing CVD risk factors, prevention efforts should include efficacious and cost-effective therapies to both reduce the incidence of MI (primary prevention), and to prevent further cardiac events in persons who have had a CVD event (secondary prevention). Although the effectiveness of regular aspirin use for primary prevention has not been determined for the general population, aspirin use for secondary prevention has been documented to be effective and is widely recommended (6).

Although the 1989 USPSTF guidelines were specific to high-risk men, the findings in this report indicate that a high proportion of women reported taking aspirin regularly, despite the absence of any specific recommendations about prophylactic aspirin use in women. Some physicians may be prescribing aspirin for their female patients despite the USPSTF recommendations, and some women may be deciding independently to initiate aspirin use.

The proportion of adults in this survey who reported taking aspirin to reduce their risk for heart disease was higher than in a similar study in New York (7), possibly reflecting differences in physician practice patterns or differences in the age structure of the two populations. Other factors related to the prevalence of aspirin use for heart disease prevention include the underlying prevalences of CVD risk factors, of preexisting CVD, and variations in public awareness about prophylactic aspirin use.

Although this study did not distinguish between aspirin use for primary or secondary prevention, some of the findings suggest that aspirin use was more common among health-conscious persons. For example, the prevalence of aspirin use was higher among physically active persons. However, prevalence of aspirin use was higher among the elderly, men, and current and former smokers, suggesting that aspirin may have been used for secondary prevention.

The findings in this report are subject to at least three limitations. First, data about regular aspirin use for heart disease prevention was self-reported. As a result, respondents may have overreported aspirin use if they confused prophylactic use with the use of aspirin-like drugs (e.g., ibuprofen) for reasons other than CVD prevention. Second, because aspirin use for primary or secondary prevention was not distinguished, the extent to which the results represent use for primary prevention or for therapy initiated following important cardiovascular events (e.g., MI or stroke) could not be determined. However, based on National Health Interview Survey findings, the prevalence of ischemic heart disease was 6.1% for U.S. adults aged 45-64 years and 15.3% for adults aged greater than or equal to 65 years (8). By assuming that all patients with ischemic heart disease use aspirin regularly, most regular aspirin users in Wisconsin and Michigan probably were using this drug for primary prevention. Third, although the data were adjusted for age and separate analyses were performed for men and women, some of the findings may be confounded by unmeasured CVD risk factors (e.g., hypertension and high cholesterol).

Since collection of the BRFSS data in Wisconsin and Michigan, the second USPSTF report concluded that evidence was insufficient to recommend for or against prophylactic aspirin use for primary prevention of MI in asymptomatic men or women (9). Data were insufficient to determine whether the reduced risk for MI in low-risk men is outweighed by the potential risks for adverse effects associated with long-term aspirin use (e.g., gastrointestinal ulceration, hemorrhagic stroke, and sudden death) (3,9). The findings in this report indicate that substantial proportions of the populations in Wisconsin and Michigan used aspirin regularly to prevent heart disease, despite the lack of conclusive data on the relative benefits and harms when used for primary prevention. The state health departments in Michigan and Wisconsin are conducting studies to determine whether patients consult their physicians before initiating regular aspirin use for primary prevention of CVD and whether their prophylactic aspirin use is appropriate given their risk factor profile and possible contraindications.

References

1. Antiplatelet Trialists' Collaboration. Secondary prevention of vascular disease by prolonged antiplatelet treatment. Br Med J 1988;296:320-31.

2. Fuster V, Cohen M, Chesebro JH. Usefulness of aspirin for coronary artery disease. Am J Cardiol 1988;61:637-40.

3. Anonymous. Final report on the aspirin component of the ongoing Physicians' Health Study. N Engl J Med 1989;321:129-35.

4. US Preventive Services Task Force. Aspirin prophylaxis. In: US Preventive Services Task Force. Guide to clinical preventive services. 1st ed. Baltimore, Maryland: Williams and Wilkins, 1989.

5. American Heart Association. Heart and stroke facts: 1997 statistical update. Dallas, Texas: National Center, 1997; AHA publication no. 55-0524.

6. Smith SC Jr, Blair SN, Criqui MH, et al. Preventing heart attack and death in patients with coronary disease. Circulation 1995;92:2-4.

7. Murray JA, Lewis C, Pearson TA, Jenkins PL, Nafziger AN. Prevalence and population characteristics of aspirin use in the primary and secondary prevention of cardiovascular disease. Am J Epidemiol 1995;141:S71.

8. Adams PF, Marano MA. Current estimates from the National Health Interview Survey, 1992. Vital Health Stat 1994;10:189.

9. US Preventive Services Task Force. Aspirin prophylaxis for the primary prevention of myocardial infarction. In: US Preventive Services Task Force. Guide to clinical preventive services. 2nd ed. Baltimore, Maryland: Williams and Wilkins, 1996.

TABLE 1. Crude and age-adjusted prevalence* of aspirin use to prevent cardiovascular disease among adults aged >=45 years,
by selected demographics and risk factor groups -- Wisconsin, 1991, and Michigan, 1994, Behavioral Risk Factor Surveillance System
====================================================================================================================================
                                                            Crude prevalence                          Age-adjusted prevalence
                                                         ---------------------------             -----------------------------------
Category                             Sample size           %                  SE +                    %                     SE
------------------------------------------------------------------------------------------------------------------------------------
DEMOGRAPHICS
  State &
   Wisconsin                                 548          19.5                1.8                   19.1                    1.8
   Michigan                                 1137          25.3                1.4                   25.5@                   1.4
  Age group yrs &
   45-54                                     577          16.0                1.6                    --                     --
   55-64                                     434          22.0                2.0                    --                     --
   65-74                                     424          28.8                2.3                    --                     --
    >=75                                     250          33.3                3.2                    --                     --
  Sex &
   Male                                      684          26.7                1.8                   27.7 **                 1.8
   Female                                   1001          20.4                1.4                   20.1                    1.3
  Race ++
   White                                    1513          23.5                1.2                   23.4                    1.1
   Black                                     126          19.6                3.7                   20.4                    3.8
   Other                                      43          28.4                8.3                   34.2                    8.3
  Education
   Less than high school                     327          25.5                2.5                   24.5                    3.0
   High school graduate                      653          23.0                1.7                   23.1                    1.7
   Some college                              344          23.2                2.5                   24.5                    2.4
   College graduate                          361          22.0                2.4                   24.9                    2.7
  Income
          <$10,000                           226          29.8                3.4                   31.8                    3.9
   $10,000-$19,999                           379          25.4                2.4                   22.8                    2.4
   $20,000-$34,999                           396          23.9                2.2                   24.5                    2.3
   $35,000-$49,999                           206          18.8                2.9                   24.6                    3.9
         >=$50,000                           309          19.7                2.4                   27.9                    4.4
   Unknown/Refused                           169          22.9                3.4                   19.9                    3.1

RISK FACTORS
  Smoking status &
   Current &&                                349          21.1                2.3                   25.5 @                  3.0
   Former &&                                 590          29.5                2.0                   28.8 @                  1.9
   Never                                     741          18.8                1.5                   18.0 @@                 1.5
  Activity level &
   Active ***                                722          25.5                1.8                   26.3 @                  1.8
   Inactive                                  949          21.2                1.4                   20.8                    1.4
  Overweight +++
   No                                       1083          23.9                1.4                   23.5                    1.4
   Yes                                       576          22.7                1.8                   23.5                    1.8
  Risk-score &&&
   None                                      416          25.7                2.3                   25.3                    2.2
   One                                       679          24.5                1.8                   23.8                    1.8
   Two                                       478          19.2                1.9                   19.9                    1.9
   Three                                      67          21.8                5.4                   17.1                    4.1

Total                                       1685          23.3                1.1                    --                     --
------------------------------------------------------------------------------------------------------------------------------------
*   Age-adjusted using the pooled age distribution from both data sets.
+   Standard error.
&   Statistically significant chi-square test of association (p<0.05) between variable and aspirin use.
@   p<0.05.
**  p<0.01.
++  Numbers for races other than black and white were too small for meaningful analysis.
&&  Current -- persons who reported having smoked at least 100 cigarettes during their lifetimes and who
    smoke now. Former -- persons who reported having smoked at least 100 cigarettes and who do not smoke now.
@@  Reference group used for pairwise statistical testing of multiple level variable.
*** Persons who undertook leisure-time physical activity for at least 20 minutes three or more times a week
    during the previous month.
+++ A body mass index of >27.3 for women and >27.8 for men.
&&& The number of risk factors present where risk factors are current smoking, overweight, and physical inactivity.
====================================================================================================================================

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