I think it's fair at this point to say there is a clear relationship. The earliest article I have in my (relatively cursory) research file on the metabolic relationship for AD is from 1994:
Fukuyama, Hidenao, Masafumi Ogawa, Hiroshi Yamauchi, Shinya Yamaguchi, Jun Kimura, Yoshiaru Yonekura, and Junji Konishi. “Altered Cerebral Energy Metabolism in Alzheimer’s Disease: A PET Study.” Journal of Nuclear Medicine 35, no. 1 (January 1, 1994): 1–6.
Here are some more recent reviews discussing the connection (recent reviews are good not just because they take into account the latest developments, but they also give you better references to go through for further research). Note, these reviews are from completely different/unrelated research teams from different countries:
Yoon, Ji Hye, JooHyun Hwang, Sung Un Son, Junhyuk Choi, Seung-Won You, Hyunwoo Park, Seung-Yun Cha, and Sungho Maeng. “How Can Insulin Resistance Cause Alzheimer’s Disease?” International Journal of Molecular Sciences 24, no. 4 (February 9, 2023): 3506. https://doi.org/10.3390/ijms24043506.
Rhea, Elizabeth M., Manon Leclerc, Hussein N. Yassine, Ana W. Capuano, Han Tong, Vladislav A. Petyuk, Shannon L. Macauley, et al. “State of the Science on Brain Insulin Resistance and Cognitive Decline Due to Alzheimer’s Disease.” Aging and Disease, August 17, 2023, 0. https://doi.org/10.14336/AD.2023.0814.
Kshirsagar, Viplav, Chetan Thingore, and Archana Juvekar. “Insulin Resistance: A Connecting Link between Alzheimer’s Disease and Metabolic Disorder.” Metabolic Brain Disease 36, no. 1 (January 2021): 67–83. https://doi.org/10.1007/s11011-020-00622-2.
