How to balance health issues with being a founder?

To be fair: some clinicians are hopeless at reading research documents. See, for example, Gerd Gigerenzer's book "Reckoning With Risk" where clinicians are asked to interpret some stats and they fail hard.

Having said tuat I tend to agree with you. Some health problems (and thyroidism is one) have large communities on the Internet and some of those communities are full of cranks.

There are most certainly conflicting interpretations: your interpretation of the document and the medical professional's interpretation of the document. It's just like how if both you and, say, a journalist or a firefighter read the same piece of code; you would have two wildly different interpretations.

Look, while I can't claim to know your situation, 9 times out of 10 it is a very bad idea to do self-diagnosis over the internet vs. taking professional advice. Even if you have a pretty good idea of what might be ailing you, there are subtle nuances to all kinds of diseases and conditions that doctors tend to understand. If you've already got second (maybe even third) opinions already, and you've come to the conclusion that none of the doctors in your area know what they're talking about, you should probably move. I don't see what other options you have here, particularly if you require prescribed medications. You might even be able to find other employment that way.

As for the startup, yes, it's unfortunate that it will tank without you, but the way you've described it, you're literally killing yourself slowly. It will end the same way regardless. You are doing NOBODY a favor by continuing on, least of all yourself.

PS Exactly how expensive are your Vitamin D supplements? They're ridiculously cheap in the US, maybe $15 for 90 capsules. International shipping might still come out cheaper.