Healthy Lifestyle Can Reduce Women's Heart Disease Risk

Summarized by Vicky Bourneuf
October 30, 2000 (Reviewed: February 2, 2003)

Introduction

Diet and lifestyle can affect the incidence of coronary heart disease (CHD). But typically, different risk factors and their effects on the risk for CHD are studied individually. Because people follow common lifestyle patterns, this study was designed to assess the effect of a combination of lifestyle practices, including diet, on the risk of CHD. Researchers estimated the proportion of coronary events that could potentially be prevented by adhering to a set of dietary and behavioral guidelines. Their effect on the risk for stroke was also assessed in a second analysis of the data.

Method

Researchers followed 84,129 women participating in the Nurses' Health Study. All participants were free of diagnosed cardiovascular disease, diabetes and cancer at the study's baseline in 1980. Participants completed follow-up questionnaires every 2 years. Each questionnaire asked for information about weight, cigarette smoking, menopausal status, physician-diagnosed hypertension and high cholesterol levels. Self-reports of these diagnoses were quite accurate when compared with medical records.

Information on physical activity was first obtained in 1980 and updated every 2 years in 1982 through 1992 using a previously validated questionnaire.
Diet was assessed using a food-frequency questionnaire that was previously validated in this population. The intake of six dietary factors was estimated. Participants reported how often, on average, they consumed common portions of foods during the previous year. Nutrient intake was calculated by multiplying the frequency of consumption by each food's nutrient content by a pre-determined common portion size. Six dietary factors were considered - trans fatty acids, glycemic load, folate, cereal fiber, n-3 marine fatty acids and polyunsaturated to saturated fat ratio. The women were allocated to groups based upon quintiles of nutrient intake.

Information on multi-vitamin supplements and single-vitamin supplements was obtained in addition to food intake data. Beer, wine and liquor intake were also recorded.

For variables other than diet and exercise, the most recent information was used. BMI and smoking status were updated every two years and alcohol intake in 1984, 1986 and 1990. To obtain the best estimate of long-term dietary intake and physical activity, a cumulative update method was used, which takes the average of all previous dietary and exercise data. For all other variables, the most recent information was used for statistical analysis.

A Low-Risk Category was established, using the following criteria:

• Those who had stopped smoking or had never smoked.
• Consumption of 5g of alcohol or more per day. Since only 1.2% reported consuming 45 g or more of alcohol per day, an upper limit was not established.
• An average activity level of at least a half-hour per day of vigorous activity - defined as activities requiring 3 or more METs per hour. This cutoff excluded walking at an easy or normal pace but included brisk walking.
• Body Mass Index 25 or less.
• A dietary score in the highest 40% (upper 2 quintiles) of a composite measure based on a diet low in trans-fat and glycemic load; high in cereal fiber, marine n-fatty acids, and folate, and with a high ratio of polyunsaturated to saturated fat. The cutoff point for the most favorable quintile was: 1.56% of energy from trans-fat; a polyunsaturated to saturated fat ratio of more than 0.43; consumption more than 4.2 g of cereal fiber per day, a glycemic load of less than 723 units per day, more than 0.1% of energy from marine n-3 fatty acids, and consumption of more than 525 microgram of folate per day.

Each 2-year interval was treated as an independent observation. Researchers simultaneously adjusted for age, time period (7 periods total), presence or absence of parental history of myocardial infarction before age 60, menopausal status and postmenopausal hormone use, presence or absence of hypertension and high cholesterol levels. Initial analysis included only diet, smoking and exercise. Body mass index and finally alcohol use was added to the analysis to examine all five factors simultaneously.

Results

During 14 years of follow-up, 1,128 heart disease events were documented - 832 nonfatal myocardial infarctions and 296 deaths from coronary heart disease. The number of strokes documented was 705.

The single most important factor was smoking, with a relative risk of 5.48 (95% confidence interval, 4.67-6.42) for those who smoked 15 or more cigarettes per day, as compared with non-smokers. Smoking 1 to 14 cigarettes per day had a relative risk of 3.12 (95% confidence interval, 2.50-3.90).

Each of the risk factors independently and significantly predicted risk, even after adjustment for family history, age, presence or absence of diagnosed hypertension, diagnosed high cholesterol levels and menopausal status. Individual components of the low-risk profile showed a significant and substantial association with risk, and each component of the dietary score was independently significant.

Women in the Low-Risk Category (who made up 3% of the population) for all five factors considered together, compared to all other women, had a relative risk of 0.17 (95% confidence interval, 0.07-0.41). The population-attributable risk was 82%, suggesting that 82% (95% confidence interval, 58%-93%) of the coronary events in the cohort might have been prevented if all women were in the low-risk group. Those in the category for four of the risk factors had a relative risk of 0.34 and a population-attributable risk of 64%, and those in the category for three risk factors had a relative risk of 0.43 and a population-attributable risk of 54%.

An analysis of the 78% of the women who were not currently smoking and in the low-risk category for the remaining four risk factors showed a relative risk of 0.25 (95% confidence interval, 0.10-0.60) compared to all other current non-smokers. The population-attributable risk was 74%, suggesting that among the nonsmokers, 74% of coronary disease events might have been prevented by compliance with the remaining components of the low-risk index.

Inclusion of stroke together with coronary artery events (i.e. analyzing the risk of any cardiovascular event) yielded a relative risk of 0.25, with a population-attributable risk of 74% - values not significantly different from those for coronary events alone.

Comment

The researchers concluded, "Among women, adherence to lifestyle guidelines involving diet, exercise, and abstinence from smoking is associated with a very low risk of coronary heart disease."

These results underscore the importance of looking at patient's "total lifestyle" and making sure that all physicians, dietitians, and other health professionals coordinate patient education efforts, which should include dietary instruction as well as an exercise plan, and smoking cessation education, if warranted.

Source

• Primary Prevention of Coronary Heart Disease in Women through Diet and Lifestyle. MJ. Stampfer, FB. Hu, JE. Manson,  et al., N Engl J Med, 2000, vol. 343, pp. 16--22

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