Objective: To evaluate the maximum benefits of dietary modification or smoking cessation to the life expectancy of North American adults.
Design: Using a computer model, we estimated the change in life expectancy for men and women following risk factor modification. We then estimated the total number of adults who would be targeted by national guidelines and the total person-years of life that would be saved.
Patients: Men and women aged 30 to 74 years who were free of coronary heart disease.
Interventions: Smoking cessation or serum cholesterol-reducing diets with 8% to 10% saturated fat and 240 to 300 mg of daily cholesterol, respectively.
Results: On average, dietary modification would reduce serum cholesterol levels from 0.45 mmol/L (17.4 mg/dL) to 0.75 mmol/L (29.1 mg/dL) in men and 0.12 mmol/L (4.6 mg/dL) to 0.55 mmol/L (21.4 mg/dL) in women, thereby increasing life expectancy by 0.03 to 0.4 year and 0.01 to 0.16 year, respectively. Smoking cessation would increase life expectancy from 2.59 to 4.43 years among men and from 2.6 to 3.68 years among women. Among adult Canadians, dietary modification would save 373,000 to 683,000 person-years of life. The majority of these benefits would occur among men who start dieting at ages 30 to 59 years. Smoking cessation would add more than 4 million person-years of life to the Canadian population. The relative impact of either intervention among American adults would be similar to these Canadian estimates.
Conclusions: Younger men, aged 30 to 59 years, might live slightly longer after dietary change, but among women and older men the average benefits would be negligible. The benefits of smoking cessation are more uniform across age and sex and are substantially greater than those predicted for dietary change.