Table 1. Studies reporting a negative effect of smoking on semen parameters.

Study No.	Author	Year	Study type	No. of participant	No. of smoker	No. of non-smoker	Study group	Association between semen parameters and smoking
								Motility	Concentration	Morphology
1	Osser et al [58]	1992	Prospective	350	186	164	Infertile smokers vs. infertile non-smokers	No	No	No
2	Künzle et al [10]	2003	Prospective	1,786	655	1,131	Infertile smokers vs. infertile non-smokers	Yes	Yes	Yes
3	Chia et al [59]	1998	Prospective	243	152	91	Healthy population	No	No	No
4	Dikshit et al [60]	1987	Prospective	626	219	288	Infertile smokers vs. infertile non-smokers	No	No	No
5	Dunphy et al [61]	1991	Prospective	330	135	195	Infertile smokers vs. infertile non-smokers	No	No	No
6	Gerhard et al [62]	1992	Prospective	225	136	89	Infertile smokers vs. infertile non-smokers	No	No	No
7	Hassa et al [63]	2006	Prospective	223	126	97	Infertile smokers vs. infertile non-smokers	No	No	No
8	Vogt et al [14]	1986	Prospective	333	150	183	Healthy population	No	No	No
9	Colagar et al [19]	2007	Prospective	101	53	48	Infertile smokers vs. infertile non-smokers and fertile smokers compared to infertile smokers	Yes	Yes	Yes
10	Jeng et al [64]	2014	Prospective	192	103	89	Healthy population	No	No	Yes
11	Lewin et al [8]	1991	Prospective	675	293	382	Healthy population	No	Yes	NA
12	Liu et al [65]	2010	Prospective	147	68	79	Infertile smokers vs. infertile non-smokers	Yes	Yes	Yes
13	Mak et al [66]	2000	Prospective	87	18	69	Infertile smokers vs. infertile non-smokers vs. fertile non-smokers	No	No	No
14	Merino et al [30]	1998	Prospective	358	197	161	Infertile smokers vs. infertile non-smokers	Yes	Yes	Yes
15	Ochedalski et al [67]	1994	Prospective	70	40	30	Infertile smokers vs. infertile non-smokers	Yes	Yes	No
16	Oldereid et al [68]	1989	Prospective	350	147	203	Infertile smokers vs. infertile non-smokers	No	No	No
17	Richthoff et al [20]	2008	Prospective	302	217	85	Healthy population	No	No	NA
18	Saleh et al [2]	2002	Prospective	65	20	32	Infertile smokers vs. infertile non-smokers	No	No	No
19	Sepaniak et al [69]	2006	Prospective	108	51	57	Infertile smokers vs. infertile non-smokers	No	No	No
20	Sergerie et al [12]	2000	Prospective	97	69	28	Healthy population	No	No	No
21	Trummer et al [3]	2002	Prospective	1,104	478	517	Infertile smokers vs. infertile non-smokers	No	No	No
22	Zavos et al [70]	1998	Prospective	40	20	20	Healthy population	Yes	Yes	Yes
23	Zhang et al [71]	2000	Prospective	362	191	110	Infertile smokers vs. infertile non-smokers vs. fertile non-smokers	Yes	Yes	Yes
24	Kiziler et al [72]	2007	Prospective	71	26	22	Infertile smokers vs. infertile non-smokers vs. fertile non-smokers	Yes	Yes	Yes
25	Shaarawy et al [73]	1982	Prospective	40	20	20	Healthy population	No	Yes	Yes
26	Shen et al [74]	1997	Prospective	60	28	32	Healthy population	No	No	No
27	Yu et al [75]	2014	Prospective	322	147	175	Healthy population	No	No	NA
28	Taha et al [76]	2012	Prospective	160	80	80	Healthy population	Yes	Yes	Yes
29	Martini et al [77]	2004	Retrospective	3,546	372	3,174	Infertile smokers vs. infertile non-smokers	No	No	No
30	Meri et al [78]	2013	Retrospective	960	396	564	Infertile smokers vs. infertile non-smokers	Yes	No	Yes
31	Pasqualotto et al [79]	2006	Retrospective	889	367	522	Healthy population	No	No	No
32	Ramlau-Hansen et al [80]	2007	Retrospective	2,542	1,052	1,490	Healthy population	Yes	Yes	NA
33	Zhang et al [1]	2013	Retrospective	1,512	737	775	Infertile smokers vs. infertile non-smokers	Yes	No	Yes

All studies evaluated semen parameters according to the World Health Organization guidelines at the time the study was conducted.

NA: not applicable.