title: New methods shed light on age of onset as a risk factor for nicotine dependence.
abstract: BACKGROUND
  Early onset of substance use is a risk factor for later drug use, abuse, and dependence. This study examines how the rate of nicotine dependence differs as a function of age of onset of regular smoking in continuous time, in order to identify critical age periods that are most predictive of later dependence for males and females.
  
  
  METHODS
  Time-varying effect modeling (TVEM) can reveal specific ages of onset that confer greatest risk for adult nicotine dependence. The rate of dependence in adulthood is modeled as a flexible function of age of onset using a subset of adults (N = 15,748) from the National Epidemiologic Survey on Alcohol and Related Conditions who ever smoked regularly.
  
  
  RESULTS
  The peak risk of adult nicotine dependence coincides with onset of regular use at approximately 10 years old, with an elevated risk persisting to 20 years. The risk of dependence is significantly higher for females compared to males for onset of regular use between ages 9 and 18.
  
  
  CONCLUSIONS
  Results suggest that the risk of adult nicotine dependence is highest when onset of regular smoking occurs at around 10 years, though the associated risk is high for ages of onset into young adulthood. Early onset of regular use is a relatively stronger risk factor for adolescent females than males. Smoking prevention programs should focus on late childhood through early adolescence, particularly among females. TVEM provides a more nuanced understanding of the risk associated with different ages of onset of health risk behaviors.
authors.affiliation: The Methodology Center, The Pennsylvania State University, University Park, PA, USA; Department of Biobehavioral Health, The Pennsylvania State University, University Park, PA, USA. Electronic address: SLanza@psu.edu.
authors.forename: Stephanie T
authors.initials: ST
authors.lastname: Lanza
authors.affiliation: The Methodology Center, The Pennsylvania State University, University Park, PA, USA; College of Health and Human Development, The Pennsylvania State University, University Park, PA, USA.
authors.forename: Sara A
authors.initials: SA
authors.lastname: Vasilenko
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012737:Sex Factors; D014029:Tobacco Use Disorder / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology; D055815:Young Adult
keywords: Age of onset; Cigarette smoking; Nicotine dependence; Sex differences; Time-varying effects