Depressive symptom mediates the association between the number of chronic diseases and cognitive impairment: a multi-center cross-sectional study based on community older adults oleh Li-Chong Lai, Dong-Mei Huang, Jie Peng, Xiao-Ying Cao, Xiao-Ling Feng, Pin-Yue Tao, Xiao Pan, Qi-Ni Pan, Deng-Jing Fan, Shu-Yu Lu, Cai-Li Li, Yan-Fei Pan, Peng-Xin Dong, Yi-Dan Chai, Ping- Huang, Hai-Chen Wu, Hui-Qiao Huang