F2RL3 Methylation as a Biomarker of Current and Lifetime Smoking Exposures

http://dx.doi.org/10.1289/ehp.1306937

Table 2. Smoking characteristics and F2RL3 (CpG_4) methyla­tion intensity of the study population.
Characteristic Current smokers (n = 654) Former smokers (n = 1,136)
na Methylation intensity [median (Q1–Q3)] p‑Valueb na Methylation intensity [median (Q1–Q3)] p‑Valueb
Q, quartile.
aSum does not always add up to total due to missing values; information on age at initiation and duration of smoking was missing for 66 former smokers and 35 current smokers; information on pack-years was missing for 165 former smokers and 73 current smokers; information on intensity of smoking was missing for 83 current smokers; information on time since cessation of smoking was missing for 14 former smokers. bKruskal–Wallis test for group differences. ­cCategories for former smokers are: 10–14/15–19/20–24/25–56. dCategories for former smokers are 1–9/10–19/20–29/30–60. eCategories for former smokers are 0.5–9/10–19/20–29/30–101.
Age at initiation of smoking (years)c            
10–14 25 0.58 (0.51–0.61)   40 0.76 (0.63–0.81)  
15–19 287 0.60 (0.52–0.71)   583 0.77 (0.70–0.82)  
20–24 174 0.62 (0.53–0.72)   273 0.78 (0.71–0.82)  
25–62 133 0.65 (0.56–0.75) 0.008 174 0.77 (0.67–0.82) 0.18
Lifetime duration of smoking (years)d            
1–19 17 0.68 (0.54–0.75)   107 0.82 (0.78–0.85)  
20–29 57 0.64 (0.56–0.72)   300 0.80 (0.76–0.84)  
30–39 279 0.62 (0.53–0.72)   320 0.77 (0.71–0.82)  
40–60 266 0.61 (0.52–0.70) 0.13 343 0.70 (0.63–0.78) < 0.0001
Cumulative dose of smoking (pack-years)e            
0.2–9 43 0.72 (0.68–0.80)   243 0.81 (0.77–0.84)  
10–19 68 0.69 (0.56–0.76)   256 0.78 (0.74–0.82)  
20–29 127 0.62 (0.54–0.71)   208 0.74 (0.67–0.80)  
30–147 343 0.59 (0.51–0.68) < 0.0001 264 0.71 (0.64–0.78) < 0.0001
Current intensity of smoking (average number of cigarette/day)            
1–9 89 0.72 (0.61–0.79)        
10–19 153 0.62 (0.52–0.69)        
20–29 235 0.60 (0.53–0.69)        
30–60 94 0.56 (0.48–0.64) < 0.0001      
Time since cessation of smoking (years)            
1       40 0.66 (0.59–0.74)  
2–4       99 0.70 (0.62–0.79)  
5–9       145 0.72 (0.65–0.79)  
10–19       335 0.76 (0.69–0.82)  
20–50       503 0.80 (0.75–0.84) < 0.0001