What should we do regarding a type 1 diabetic with mild dementia who is hiding insulin dosing?

With type I and a pump it is crucial to discuss this with an MD.
Go with your father to his doctor.
A failure to make the decision for more care (if needed) could result in death.

I wouldn't assume he's trying to "prove" anything. Early symptoms of dementia can be memory loss, confusion, "stubbornness" (diminished logic and reasoning skills), and paranoia.

He now cannot be trusted to manage his meds at all, so he either needs an appropriate person to do this for him (a qualified in-home aid and the meds not kept where he can find them) or he goes to AL and pays for meds management service (which often is an "a la carte" extra expense). IDK how it would all work with an insulin pump, maybe he doesn't use one any more so that he won't overdose himself.

He cannot have access to medications any longer. His caregivers must provide medications at the appropriate times and keep them secured from him at all other times

For starters, his insulin and all other medications should be kept in a locked strong box. People with dementia should not have any access to medications nor should they be reponsible for any. Someone should be giving him whatever medications he takes and doing his insulin for him.
Make his meds inaccessible and start administering them yourself or get homecare to come.

If he cannot control his diabetes may be time for an Assisted Living wherevhis medscwill be monitored by a Nurse.

Someone with dementia should not have access to medications and should not be medicating themselves. If he does not have people with him full time that can give his medications and test him as needed, he should move to a facility where they have staff to do that.

Memory care is needed in a place where all of his meds are handled by the nurses and med tech

I have had Type 1 Diabetes for over 30 years and use an insulin pump and a continuous glucose monitor. First, giving up control of his insulin dosing may be very difficult and scary for him and he may have never been able to trust others to help him with that. If he has made it to this point in life as a Type 1, he has had to be extremely vigilant in taking care of this aspect of his life and done a helluva job. As for the pump, all the ones I have used can be locked to require a password. His caregivers will need to become experts in insulin dosing, what to do if he gets too much or too little, etc. That last part happens no matter how vigilant we are...it is not an exact science. And finally, if he does not wear a continuous glucose monitor (like a Dexcom), medicare covers it, and he definitely should and have it monitored by a vigilant caregiver. It can help make dosing decisions, and may well save his life.

If he has been managing his pump for a long time there could certainly be some “proving” or hiding going on but there is very likely some fear of not having the control as well. As a type 1 diabetic he I’m sure is all too aware of what happens and what can happen if his blood sugar gets extremely high or extremely low and making himself so totally vulnerable to caregivers is a very scary thing. If he has a CGM (and he should) I know my Moms at least sent reports to her endocrinologist so they saw if she was having highs or lows and would contact us about that or at least discuss it at her 3 month visits so I would urge you to contact his endo and let them know your concerns so they can bring it up with him as their concern and maybe brainstorm another safeguard.

I can tell you what we did progressively with our mom. She was a type 2 so a little different but she managed her diabetics so poorly for years that she not only had other issues as a result but it became necessary for her to be treated as a type 1. When she first got the Dexicom our lives and her management got much better because we were able to see her blood sugar in real time as well and could set notifications for highs or lows while we could still contact her to correct them. For your dad it sounds like this would be more of a back up for now but it would be his children following his numbers and reminding him rather than a non related caregiver and if it got too far it sounds like there would be a caregiver with him who could give him glucose for example, at your direction, if he wasn’t able.

By the time Mom got an insulin pump she wasn’t able to get into her phone never mind figure out a bolus. The Omnipod, which is what she had, at least required a code to get into the app so that made it harder for her since she her dementia was such that she couldn’t remember the steps. The pump meant she needed someone with her even more of the time too which wasn’t a bad thing but because we had the Dexicom info all the time we could see things trending in the wrong way and that made it easier to work with caregivers for us as well. Her caregiver would always call (me mostly) when one of us wasn’t around to go over what she was eating and how many carbs or how much of a bolus to give her and she felt comfortable with the fact that we were overseeing it and making the decisions. Yes this required one of us to be available for inputs but it made all of us more comfortable and it allowed for multiple back ups, my brother and I often consulted on what to give her. Maybe you can start to work into consulting with your dad on it so he can “train” you for when he is no longer able to do it for himself. One thing that did sell Mom on the whole thing was not having to prick her finger and give herself shots (which started to often miss) anymore.

Good luck this push and pull between independence and letting go is never easy.

At the risk of sounding morbid, perhaps the father does not want to go to his death with dementia, becoming completely dependent on others, and is consciously or subconsciously letting high dose, too much, take him sooner than later. Forgive me; just a hunch. The suggestions to place him where his meds are monitored sounds best.