T1 diabetes is a strange disease, my brother has it and he was not remotely over-weight although in college and after, his diet was terrible(he also was extremely vitamin D deficient from avoiding the sun). He developed it in his late 20's. Another friend has it and he got it as a kid, he said it came on after a very bad bout of pneumonia he had beforehand, and his Dr's think that is what may have triggered it but who can say. Perhaps either a extremely hard illness or a vitamin deficiency can bring it on, covid-19 seems to fit the bill with accounts of people with low vitamin D levels getting more severe cases, and the fact that it attacks the entire body looking for weaknesses.