Healthy lifestyle factors and prevention of coronary heart disease

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Hypertension and high lipid levels are modifiable cardiovascular risk factors. Although drug treatment can reduce these cardiovascular risk factors as well as the risk of coronary heart disease (CHD), improving lifestyle behaviors can increase the comparatively moderate (20%-30%) improvement achieved with medication.^1,2

Many lifestyle habits, such as eating a healthy diet, increasing physical activity, not smoking, and maintaining normal weight, also improve hypercholesterolemia and hypertension, in addition to improving other potential risk factors, such as increased homocysteine levels and glucose intolerance. Although each healthy lifestyle factor decreases the risk of CHD,³ the most benefit can be achieved by combining lifestyle factors, as has been shown in studies of elderly men and women⁴ and middle-aged women.⁵ However, few studies have evaluated the association between CHD and a combination of healthy lifestyle changes in middle-aged and older men.

In the Health Professionals Follow-Up Study (HPFS),⁶ we examined the effect of modifiable lifestyle factors on the risk of CHD among educated middle-aged and older men. We also examined whether a healthy lifestyle would further benefit men who were receiving drug therapy for increased lipid levels and hypertension, as well as the relationship between lifestyle modifications later in life and the risk of CHD.

Subjects and methods

We included 42,847 male health professionals in the HPFS.⁶ All men were 40 years of age or older at the start of the study in 1986 and free of known chronic disease, including cardiovascular disease, diabetes, and cancer. Information on medical conditions and lifestyle factors was collected through self-administered questionnaires.

Parental history of myocardial infarction (MI) and height were reported on the 1986 questionnaire. Every 2 years, we updated information on the participants’ smoking status, medication use, physician-diagnosed hypertension and hypercholesterolemia, body weight, and physical activity. A food frequency questionnaire, which was given every 4 years, was used to evaluate dietary information.

We defined a level that was considered to be low risk for each of the lifestyle factors: alcohol consumption, diet score, physical activity, optimal weight, and smoking. Moderate alcohol consumption was defined as an average of ½ a drink to 2 drinks per day. For diet, a diet score was computed from the Alternate Healthy Eating Index. A high score resulted from multivitamin use; a high intake of vegetable protein, fish, chicken, vegetables, fruits, cereal fiber, and polyunsaturated fats; and a low intake of trans fat and red or processed meats. A diet score in the top 40% of the cohort distribution was considered to be a low-risk diet. Thirty minutes or more of moderate-to-vigorous exercise per day was considered to be low risk. A body mass index (BMI) of < 25 kg/m², the usual classification for overweight, was considered optimal weight. Men who were not currently smoking were considered to be low risk. By adding the total number of low-risk lifestyle factors, we obtained a healthy lifestyle score, ranging from 0, which was the least healthy, to 5, which was the healthiest.

We used Cox proportional hazards models to assess the association between healthy lifestyle factors and the risk of CHD, defined as nonfatal MI and fatal CHD, occurring between 1986 and 2002. All models were adjusted for age, parental history of MI, history of hypertension and hypercholesterolemia, aspirin use, and antihypertensive medication use. We calculated the population-attributable risk to estimate the proportion of cases of CHD within the population that may have been prevented by following a healthy lifestyle.

Results

Over 16 years of follow-up, 2183 cases of CHD occurred. As shown in the

, each healthy lifestyle factor in the healthy lifestyle score showed a significant inverse relationship with risk of CHD, even when all 5 factors were modeled simultaneously.

Table

P

Figure 1 shows that there was an inverse relationship between the healthy lifestyle score and the risk of CHD ( for trend < .001). Compared with men with no low-risk factors, those at low risk for 1 or more factors had a markedly reduced risk of CHD; the lowest risk was seen in men at low risk for all 5 factors. In addition, among men who used antihypertensive or cholesterol-lowering medications, there was a marked inverse relationship between the healthy lifestyle score and the risk of CHD, as shown in Figure 2. A healthy lifestyle was associated with a lower risk of CHD among men who did not use medications as well (data not shown).

Only 4% of men were at low risk for all 5 lifestyle factors, with a population-attributable risk of 62% (95% confidence interval [CI], 49%-74%), meaning that most of the coronary disease in this group of men may be attributed to not following a healthy lifestyle. Men who were at low risk for all 5 lifestyle factors and who used antihypertensive and lipid-lowering medications had a population-attributable risk of 57% (95% CI, 32%-79%); the population-attributable risk among medication nonusers was 66% (95% CI, 49%-79%). Among middle-aged men (< 65 years of age), the population-attributable risk was 79% (95% CI, 61%-90%), which was higher than the population-attributable risk among the older men (population-attributable risk, 47%; 95% CI, 27%-68%).

Our repeated assessments of lifestyle factors and the long follow-up period permitted us to evaluate the association between CHD risk and changes in healthy lifestyle. Compared with men who did not implement healthy lifestyle changes, those who adopted at least 2 new healthy habits decreased their risk of developing CHD by 27% (95% CI, 7%-43%). Men who lowered their healthy lifestyle score by 2 or more factors, however, had a 48% (95% CI, 15%-88%) increased risk of CHD.

Discussion

If all subjects in this study had practiced low-risk lifestyle behaviors, more than half of all coronary events might have been prevented, even among those taking medication for coronary risk factors. This study also showed that improving lifestyle by adopting healthy lifestyle factors was associated with a lower risk of CHD.

The incidence of CHD continues to be elevated among individuals who use antihypertensives and lipid lowering medications, despite the known benefits of medication use. Compared with drug treatment alone, improving lifestyle by increasing physical activity and changing the diet, in addition to antihypertensive or lipid-lowering medication, has decreased coronary risk factors, including high low-density lipoprotein cholesterol levels and high blood pressure.^7,8 In our study, 57% of CHD cases among subjects who were using medication might have been prevented by adherence to this low-risk lifestyle beyond the benefits of medication use. This suggests that medications should not be used as a substitute for healthy habits, but should be used in addition to them.

Our results underscore the benefits of making positive lifestyle changes. Adopting additional low-risk behaviors, even during middle age or later in life, may lower the risk of CHD. The true benefits of healthy lifestyle changes were probably underestimated in our study because the healthiest subjects, who were already adhering to 4 or 5 factors, could not increase their score by 2 factors. This study shows that although it is important to encourage healthy lifestyle habits throughout a person’s lifetime, men can obtain significant benefit by making favorable changes during middle age and beyond. In other words, it is never too late to change.

Compared with older men, middle-aged men had a higher population-attributable risk resulting from lifestyle modifications. Among men younger than 65 years of age, the population-attributable risk was comparable to that seen in middle-aged women who participated in the Nurses’ Health Study⁵ and in studies of CHD mortality, which defined low risk using clinical measures.^9,10 But there was a significant association between healthy lifestyle factors and lower risk even among men aged 65 years and older. Among a population of elderly men and women aged 70 to 90 years, the risk of CHD mortality was 65% lower for individuals who adhered to 4 healthy lifestyle choices.⁴

To ascertain the effect of these lifestyle factors on the risk of CHD, a randomized clinical trial is the best approach. However, a clinical trial may not be ethical for certain factors, such as smoking and alcohol use. Furthermore, studying a combination of these factors, as was done in this study, would be challenging, if not impossible, in a trial with 16 years of follow-up. Although an observational study may have limitations, such as measurement error in self-reported variables, the repeated measures of lifestyle and diet and the observational design of this study permitted us to examine the results of lifestyle changes, which usually take place in free-living populations.

Conclusion

We evaluated the effects of adhering to healthy lifestyle changes among a population of male health professionals. Results of our study showed that the majority of CHD events may be prevented, even in those taking antihypertensive and cholesterol-lowering medications. These results highlight the importance of a healthy lifestyle in the primary prevention of CHD.

Acknowledgments

The authors would like to thank Walter Willett, MD, and Meir Stampfer, MD, PhD, for their comments and suggestions in the preparation of this article; Ellen Hertzmark for her statistical support; and Mira Kaufman and Betsy Frost-Hawes for their expert help.