| Summary: | Background and aimsSmoking cigarettes is a major global health problem that affects appetite and weight. The aim of this systematic review was to determine how smoking affected plasma leptin and ghrelin levels.MethodsA comprehensive search of PubMed, Scopus, Web of Science, and Ovid was conducted using a well-established methodology to gather all related publications.ResultsA total of 40 studies were included in the analysis of 11,336 patients. The overall effect showed a with a mean difference (MD) of −1.92[95%CI; −2.63: −1.20] and p = 0.00001. Subgroup analysis by study design revealed significant differences as well, but with high heterogeneity within the subgroups (I2 of 82.3%). Subgroup by sex showed that there was a significant difference in mean difference between the smoking and non-smoking groups for males (MD = −5.75[95% CI; −8.73: −2.77], p = 0.0002) but not for females (MD = −3.04[95% CI; −6.6:0.54], p = 0.10). Healthy, pregnant, diabetic and CVD subgroups found significant differences in the healthy (MD = −1.74[95% CI; −03.13: −0.35], p = 0.01) and diabetic (MD = −7.69[95% CI, −1.64: −0.73], p = 0.03). subgroups, but not in the pregnant or cardiovascular disease subgroups. On the other hand, the meta-analysis found no statistically significant difference in Ghrelin serum concentration between smokers and non-smokers (MD = 0.52[95% CI, −0.60:1.63], p = 0.36) and observed heterogeneity in the studies (I2 = 68%).ConclusionThis study demonstrates a correlation between smoking and serum leptin/ghrelin levels, which explains smoking’s effect on body weight.Systematic review registrationhttps://www.crd.york.ac.uk/ prospero/display_record.php, identifier (Record ID=326680).
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