Age has been shown to influence drug metabolism but effects of aging could be due to other variables that influence metabolism and differ with age. Plasma half-life and metabolic clearance rate of antipyrine were studied in 307 healthy male subjects, aged 18 to 92. Half-life was 16.5% longer and metabolic clearance rate was 18.5% less in a group of the older than in the younger subjects. Both caffeine and cigarette use were positively correlated with the rate of antipyrine metabolism. Multiple regression analysis showed that the effect of smoking was partially responsible for the age differences in antipyrine metabolism. Smoking explained 12% of the variance in metabolic clearance rate and age explained 3%. Our results suggest that studies attempting to quantify the effects of aging on drug metabolism must also take into account other factors that differ with age.

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Prospective follow-up information obtained between 1976 and 1981 on mortality among 2539 individuals showed that pulmonary function impairment is a risk factor for short-term mortality, even when risk factors such as age, sex, and smoking are considered. Predicted risk curves for impaired individuals (those with forced expiratory volume in one second less than 68% of forced vital capacity) are consistently higher among all race-sex categories over all ages. Survival analysis using the proportional hazards model shows a steeper decline in estimated survival among individuals with poor pulmonary function compared to those with good pulmonary function, adjusted for age, race, and smoking effects. These observations are consistent with the concept that impairment of pulmonary function is a risk factor for morbidity and mortality from several nonrespiratory as well as respiratory diseases and that it acts by contributing to various pathogenic mechanisms in different organ systems.

The hypothesis that vitamin A, or foods rich in vitamin A such as milk, protects against the development of airway obstruction was tested in a subsample of data from the 1971-1975 National Health and Nutrition Examination Survey. The relative risk (estimated by relative odds) of having airway obstruction, defined as a FEV1/FVC less than or equal to 65%, was measured for different levels of nutrient and food group intakes after adjustment for age, sex, Quetelet Index, caloric intake, and cigarette smoking. Among the white respondents (never smokers or current smokers) whose recalled diet could be considered as typical of their usual diet, the relative odds of having airway obstruction was inversely related to vitamin A intake (x2 for trend = 7.2, p less than 0.01). In the analysis by food groups, the adjusted relative odds of airway obstruction for meat and poultry were 2.4 (95% confidence limits: 1.0 to 5.8) and for milk 1.6 (95% confidence limits: 1.0 to 2.5). The association of airway obstruction with lack of vitamin A or milk intake was clearer among smokers. These findings suggest that a diet poor in vitamin A increases the risk of airway obstruction, and are consistent with the previously reported association of chronic bronchitis, milk intake, and smoking.