Systematic review with meta-analysis of the epidemiological evidence relating smoking to type 2 diabetes

Table 4 Dose-response analyses for current smoking

Grouping1	Current vs never smoking		Current vs non-smoking
	n2	RR (95%CI)	n	RR (95%CI)
Using key values:
About 10 cigs/d	13	1.10 (1.03-1.18)	13	1.04 (0.98-1.10)
About 20 cigs per d	13	1.31 (1.19-1.44)	13	1.27 (1.16-1.39)
About 40 cigs per d	13	1.55 (1.39-1.72)	13	1.54 (1.37-1.72)
Low	23	1.17 (1.11-1.23)	22	1.13 (1.07-1.19)
Medium	23	1.30 (1.22-1.39)	22	1.26 (1.18-1.34)
High	23	1.53 (1.41-1.65)	22	1.48 (1.37-1.60)
1-19 cigs/d	18	1.32 (1.20-1.45)	17	1.20 (1.10-1.30)
20+	18	1.58 (1.42-1.76)	17	1.44 (1.31-1.59)

¹The key value analysis is based on all studies which provide estimates for each key value (i.e., for a range which included the key value and no other key value). The low/medium/high analysis is based on all studies which provide estimates for exactly three levels. The 1-19, 20+ analysis is based on those studies which reported results only for these two levels.

²Number of estimates combined. CI: Confidence interval; RR: Relative risk.