Objective: To determine the role of genetic and environmental factors in the onset of smoking in Chinese male twins.
Methods: Retrospective data on initiation and age at onset of smoking, reported by 1,006 adult twin pairs [aged 18 year-old or more, 638 pairs of monozygotic (MZ) twins and 368 pairs of dizygotic (DZ) twins] were analyzed to calculate the heritability of smoking behavior and smoking initiation.
Results: Different from western culture, 66.8% of males in this Chinese sample are smokers or have the experience of smoking, but only 0.2% of females do so. In the MZ twins, 88.7% (566/638 pairs) of them are both smokers or have smoking experience or both non-smokers, while the number is 63.6% (234/368 pairs) in the DZ twins. The heritability of smoking in this Chinese twin sample is 69.0%+/-4.1%. The smokers usually started their smoking at the age of 20.4+/-5.3 years old. The correlation coefficient for age at onset of smoking in male MZ twin smokers is 0.393, compared to correlation coefficient 0.860 in male DZ twin smokers.
Conclusion: The moderate level of heritability shows that genetic factors have influence on smoking choice; when the smokers start their smoking, however, this depends more on individual environmental variation in our Chinese twin sample.