The British-Norwegian migrant study: 5-year mortality differentials due to cigarette smoking.

Cigarette smoking and 5-year survivorship of 20,017 British and 10,016 Norwegian migrants to the United States were compared with 17,696 British and 26,155 Norwegian nonmigrants. The highest mortality ratios for 5-year age-adjusted death rates observed were of cigarette smokers to nonsmokers, ranging from 1.40 to 1.60 for men and from 1.18 to 1.36 for women. Mortality ratios of nonmigrants to migrants ranged from 1.07 to 1.19 for men and from 1.22 to 1.36 for women. Mortality ratios for British to Norwegian groups ranged from 1.13 to 1.27. Some differences in mortality ratios for cardiovascular diseases contrasted with mortality ratios for noncardiovascular diseases were noted. The most important of these differences was the apparent lack of any consistent difference between nonmigrants and migrants in their 5-year cardiovascular mortality rates, although there were consistent differences for noncardiovascular diseases.