S1 Raw data -

Objective
To compare the serum levels of brain-derived neurotrophic factor (BDNF) in type 2 diabetes mellitus (T2DM) patients with healthy controls (HC) and evaluate the BDNF levels in T2DM patients with/without cognitive impairment.
Methods
PubMed, EMBASE, and the Cochrane Library databases were searched for the published English literature on BDNF in T2DM patients from inception to December 2022. The BDNF data in the T2DM and HC groups were extracted, and the study quality was evaluated using the Agency for Healthcare Research and Quality. A meta-analysis of the pooled data was conducted using Review Manager 5.3 and Stata 12.0 software.
Results
A total of 18 English articles fulfilled with inclusion criteria. The standard mean difference of the serum BDNF level was significantly lower in T2DM than that in the HC group (SMD: -2.04, z = 11.19, P <0.001). Besides, T2DM cognitive impairment group had a slightly lower serum BDNF level compared to the non-cognitive impairment group (SMD: -2.59, z = 1.87, P = 0.06).
Conclusion
BDNF might be involved in the neuropathophysiology of cerebral damage in T2DM, especially cognitive impairment in T2DM.

研究目的
比较2型糖尿病（type 2 diabetes mellitus, T2DM）患者与健康对照（healthy controls, HC）的血清脑源性神经营养因子（brain-derived neurotrophic factor, BDNF）水平，并评估伴/不伴认知障碍的T2DM患者的BDNF水平。
研究方法
检索PubMed、EMBASE及Cochrane Library数据库自建库至2022年12月发表的关于T2DM患者BDNF的英文文献。提取T2DM组与HC组的BDNF数据，采用医疗保健研究与质量局（Agency for Healthcare Research and Quality）评价研究质量，使用Review Manager 5.3及Stata 12.0软件对合并数据进行Meta分析。
研究结果
共纳入18篇符合纳入标准的英文文献。与HC组相比，T2DM组患者的血清BDNF水平的标准化均数差（standard mean difference, SMD）显著更低（SMD=-2.04，z=11.19，P<0.001）。此外，T2DM伴认知障碍组的血清BDNF水平较非认知障碍组略低（SMD=-2.59，z=1.87，P=0.06）。
研究结论
BDNF可能参与T2DM患者脑损伤的神经病理生理过程，尤其是T2DM相关认知障碍。