Smoking behavior and circulating vitamin D levels in adults: A meta‐analysis

To determine the effect of smoking on circulating vitamin D in adults, we performed a meta‐analysis. Literature before 9 May 2021 was retrieved from electronic literature databases such as EMBASE, PubMed, and Cochrane. The quality of the included studies was assessed by two researchers against the Newcastle–Ottawa scale and JBI Evidence‐based Health Care Centre criteria. All eligible studies and statistical analyses were performed using STATA 14. Twenty‐four studies with 11,340 participants meeting the criteria were included in the meta‐analysis. The results of meta‐analysis showed that the level of circulating 25(OH)D in smokers was lower than that in nonsmokers. A subgroup analysis based on vitamin D supplement use showed that both smokers who used vitamin D supplements and smokers who did not use vitamin D supplements had lower blood 25(OH)D levels compared with the control group. In addition, subjects were divided into different subgroups according to age for meta‐analysis, and the results showed that the serum 25(OH)D level in each subgroup of smokers was lower than that in the control group. This meta‐analysis revealed differences in circulating vitamin D levels between smokers and nonsmokers, with smokers likely to have lower circulating vitamin D levels.