Trends in mortality among California physicians after giving up smoking: 1950-79

A study was conducted to assess how lung cancer and other mortality trends among California physicians had been influenced by the high proportion who had given up smoking since 1950. Several sample surveys indicated that the proportion of California physicians who currently smoked cigarettes had declined dramatically from about 53% in 1950 to about 10% in 1980. During the same period the proportion of other American men who smoked cigarettes had declined only modestly, from about 53% to 38%. Using the 1950 American Medical Directory a cohort of 10 130 California male physicians was established and followed up for mortality till the end of 1979, during which time 5090 died. The information from follow up and death certification was exceptionally good. The standardised mortality ratio for lung cancer among California male physicians relative to American white men declined from 62 in 1950-9 to 30 in 1970-9. The corresponding decline in standardised mortality ratio was from 100 to 63 for other smoking related cancer, from 106 to 71 for ischaemic heart disease, and from 62 to 35 for bronchitis, emphysema, and asthma. The standardised mortality ratio remained relatively constant for other causes of death not strongly related to smoking. The overall ratio declined in all age groups at a rate of about 1% a year. The total death rate among all physicians converged towards the rate among non-smoking physicians. By the end of the study period physicians had a cancer rate and total death rate similar to or less than those among typical United States non-smokers. This "natural experiment" shows that lung cancer became relatively less common on substantial elimination of the primary causal factor, cigarette smoking. Other smoking related diseases also became relatively less common, though factors other than cigarette smoking may have contributed to this change.