Aim: To examine variation in nicotine dependence scores and covariation between different dependence symptoms.
Design: A 12-year, nationally representative, probability-based survey of adolescent health-related behaviors and their outcomes during young adulthood in the United States. The genetic contribution to nicotine dependence was evaluated in the sibling-pairs sample of the US National Longitudinal Study of Adolescent Health.
Measurements: Nicotine dependence (ND) was assessed using the Fagerström Test for Nicotine Dependence (FTND) and Heaviness of Smoking Index (HSI) in 1154 young adults, between the ages of 18 and 25 years, who were from twin, full sibling and half-sibling pairs.
Findings: Dependence in this sample was common and varied in degree. Total HSI scores evidenced moderate to large heritable contributions (61%, 95% confidence interval (CI): 0.46-0.72), as did the quantity of cigarettes smoked (52%, 95% CI: 0.39-0.63) and urgency to smoke (55%, 95% CI: 0.38-0.68). Multivariate modeling identified a highly heritable underlying factor (76%, 95% CI: 0.56-0.91) that influenced the covariation of dependence symptoms and loaded most heavily on how soon after waking a smoker uses his or her first cigarette. The quantity of cigarettes smoked per day also evidenced residual genetic influences that were not common to other dependence-related behaviors.
Conclusions: In this sample of young adults from the general population, both genes and individual-specific environments are important etiological factors in ND. The urgency to smoke, as measured by the time to first cigarette, may be the most informative measure on the FTND for genetic studies of nicotine dependence.