李 祥明 ^* Huang guizhong HUANG Huang peixing HUANG

• lxm, 广东省汕头市, China

ousnhanes/default.aspx?BeginYear=2007). We kindly request clarification on how the authors accessed these data.In addition, while we recognize the authors' comprehensive approach in controlling for var ious covariates (e.g., smoking, depression, OSA, work status, work shifts, and VD collection se ason), we would like to point out some limitations of the study. As it is based on a cross-sect ional design, the study cannot establish causal relationships between VD levels, cotinine, and i nsomnia, nor can it conclusively determine the regulating role of VD in the association betwee n cotinine and insomnia.We also wish to highlight that the study's reliance on self-reported insomnia may introduc e recall bias. Although clinical guidelines suggest that insomnia is often diagnosed through pati ent history rather than polysomnography (PSG), self-reported data remain subject to inaccuracie s. Additionally, dietary intake information, collected via two 24-hour recalls, may further contri bute to recall bias. Furthermore, we would like to expand on the geographical limitations of the study. The fi ndings from a U.S.-based cohort may not be directly applicable to regions with different seaso nal and geographical characteristics. For instance, in tropical regions with only two distinct sea sons, factors like sunlight exposure, which affect vitamin D synthesis, may differ significantly f rom those in temperate climates. We would recommend the authors discuss this limitation and caution against extrapolating these findings to populations in regions with different climates and seasonal variations.Moreover, the U.S. population sample used in this study has specific dietary patterns that may not align with those of populations in other countries. As dietary habits can significantly i nfluence vitamin D levels, this study's conclusions may not be generalizable to other regions with different dietary patterns. We encourage the authors to discuss this limitation and suggest future studies that explore these relationships in populations with varying dietary intake pattern s.We encourage further prospective studies to better elucidate the causal relationship between VD and insomnia, as well as the potential role of VD in modulating the effects of tobacco smoke exposure on sleep disturbances.Once again, we appreciate the authors' valuable contributions and look forward to seeing further research on this topic. [1] Gao T. The roles of serum vitamin D and tobacco smoke exposure in insomnia: a cross-sectional study of adults in the United States [J]. Frontiers in Nutrition.