Evidence for genetic influences on smoking in adult women twins.

The purpose of the present study was to examine genetic influences on smoking behavior in women twins, and to compare the results before and after adjusting for environmental covariates. Subjects were participants in the Kaiser Permanente Women Twins Study in Oakland, California. Exam 1 (1978-1979) included 434 pairs of women, and exam 2 (1989-1990) included 352 pairs of women. For comparison with a previous study in male twins, pairwise concordance ratios (OCR) for smoking status between monozygotic (MZ) and dizygotic (DZ) twins were calculated. Multivariate logistic regression analysis was also used to assess the association of smoking behaviors between co-twins, adjusting for age, education, and frequency of contact. At exam 1, OCR's were consistent with previous results in male twins, and supported genetic influences on smoking initiation (OCR = 1.6; 95% Confidence Interval (95% CI) = 1.0, 2.3) and maintenance (OCR = 1.8; 95% CI = 1.3, 2.4). In contrast to the males, however, no clear evidence for genetic influences on smoking intensity or never smoking were present. The adjusted logistic regression models appeared to confirm the findings from the pairwise comparisons. The results were similar for exam 2. These results are consistent with modest genetic influences on smoking initiation and maintenance. Differences between these results and those for the male twins suggest possible genetic-environmental interactions.