A synergistic effect of secondhand smoke with vitamin D deficiency on cognitive impairment in older adults: a cross sectional study - Li, Yan; Shen, Qianqian; Chen, Chengyu; Yin, Xueru; Wang, Xinru; Yang, Xiyue; Zhang, Xueqian; Chen, Lei; Xu, Jian; Gong, Guifang (Frontiers in Nutrition, 2025)