Whether dietary β-carotene and vitamin A intake protect against lung cancer risk is not clear. Therefore, we performed this meta-analysis to investigate the association between them. The related articles were searched using the databases PubMed and the Web of Knowledge up to May 2015. We used the random-effect model to estimate the relative risk (RR) and their 95% CI. Small-study effect was assessed using Egger’s test. In total, 19 studies comprising 10,261 lung cancer cases met the inclusion criteria. The pooled RR and their 95% CI was 0.855 (0.739–0.989) for higher category of dietary vitamin A intake and lung cancer risk, especially among Asian populations and in the cohort studies. Evidence from 18 studies suggested that higher category of dietary β-carotene intake could reduce lung cancer risk (0.768 (0.675–0.874)).The associations were also significant in American and Asian populations. In conclusions, higher category of dietary β-carotene and vitamin A intakes could reduce the risk of lung cancer. However, the dose-response analysis was not performed due to the limited data in each individual study. Due to this limitation, further studies with detailed dose, cases and person-years for β-carotene and vitamin A of each category are wanted to assess this dose-response association.

Hypoglossal motoneurons innervate genioglossus muscle, the contraction of which is critical in the maintenance of upper airway patency in patients with obstructive sleep apnea. As a potassium channel distributed in hypoglossal motoneurons, TWIK‐related acid‐sensitive K+ channel‐1 (TASK‐1) could be inhibited by 5‐HT. This study aimed to investigate if TASK‐1 expression in hypoglossal nucleus could be influenced by chronic intermittent hypoxia (CIH) and 5‐HT2A receptors antagonist. Two hundred twenty‐eight rats were exposed to CIH or normoxia (NO) in the presence and absence of 5‐HT 2A receptor antagonist (MDL‐100907) microinjected into the hypoglossal nucleus. The expression of 5‐HT and TASK‐1 in the hypoglossal nucleus were detected by immunohistochemistry and reverse transcription quantitative polymerase chain reaction on the 1st, 3rd, 7th, 14th and 21st day of CIH exposure. The mean optical density (MOD) of 5‐HT in the XII nucleus was significantly increased in the CIH and CIH + MDL group than the NO group on the 7th and 21st day ( p < 0.05). Compared with the NO group, the MOD and gene expression of TASK‐1 in the CIH group was significantly increased on the 7th and 14th day ( p < 0.05), then normalized on the 21st day. The TASK‐1 expression in the CIH + MDL group was significantly lower than the CIH + PBS and CIH group on the 7th and 14th day ( p < 0.05). The CIH‐induced transiently upregulation of the TASK‐1 expression in the hypoglossal nucleus could be reversed by 5‐HT 2A receptor antagonist, indicating that the modulation of the TASK‐1 expression in response to CIH involves 5‐HT and 5‐HT 2A receptors, and this CIH effect might be 5‐HT 2A receptor‐dependent.

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