Increased incidence of thyroid cancer among Norwegian women married to fishermen

The relationship between thyroid cancer in women and the occupation of their spouses was examined in a retrospective cohort study. Of the 2.9 million women registered in the Central Population Registry of Norway by the end of 1991, 1.2 million had a spouse registered with an occupation in one or more of the censuses of 1960, 1970 or 1980. These women were included in the study. Based on the first digit of their husbands' five-digit Nordic occupational code, the women were assigned to ten broad categories. A standardised incidence ratio (SIR) and 95% confidence interval were calculated for each occupational category. The women were further subdivided and analysed in 71 groups defined by the first two digits of their husband's occupational code. Among the women included in the study, a total of 2,409 cases of thyroid cancer were reported to the Cancer Registry of Norway during the period 1960-92. A significantly elevated risk of thyroid cancer was found only among women whose spouses belonged to the occupational category Agriculture, forestry or fishery (n = 208,279), with a SIR of 1.13. In the subgroup Fishing, whaling and sealing work (n = 40,839), the risk was even higher with a standardised incidence ratio of 1.91. Our data support the proposed relationship between increased risk of thyroid cancer and mode of living, more specifically dietary fish or other seafood.