I used to be vegan and vegetarian in the past and ended up with very low iron and vitamin deficiencies, despite taking supplements. So now I am back to eating a more varied diet that includes the occasional red meat. One size does not fit all, and rather than having to have iron infusions, I prefer having some animal products now and again. My blood tests look much better since I reintroduced animal products in my diet. I do not make an excess of them, but in my case vitamin B12 and iron are assimilated better from food than from supplements.
I hope your doctor is going to help you. They should most likely test both vitamin B12 and homocysteine, for good measure.

A healthy diet is a very individual thing, and we should choose what works best with us.
Diet culture now morphed into "healthy eating," "clean eating," and other such trends, and if people want to follow them for themselves, that is fine, but the reality is that they are just trends.
A variate diet has more chance of meeting all the needs of the body.

Go for it, Janice!!

I will look at the suggested articles. When asked, my doctors tend to say they don't know much about supplements. I think the MPN specialist said B12 was probably OK due to excreting any that was too much, rather than building it up in the body. I'll ask about a blood test next time I see him. I definitely feel better with more B12. Also, although some here will never do this, I feel better by adding back a little red meat in my diet. I don't think an occasional hamburger will kill me, plus it gives me happiness as a treat, but of course I'm also watching cholesterol.

Probably you need to discuss this with your doctor, as ET and vitamin B12 levels have a complex relationship. The doctor most likely should check your vitamin B12 levels and probably other biomarkers. Apparently normal levels of B12 alone in ET do not exclude occult vitamin B12 deficiency.

These are two articles on the matter:
"Our data suggest that 27.27% of the total enrolled patients had occult vitamin B12 deficiency despite normal to elevated vitamin B12 levels on regular serum vitamin B12 testing."
https://www.sciencedirect.com/science/article/a...

"In the literature, it is reported an increased incidence of arterial and venous thrombotic events in patients with associated vitamin B12 or vitamin B9 deficiency with chronic myeloproliferative syndromes since the latter are characterized by thrombocytosis while vitamin B9 and B12 deficiencies are responsible for hyperhomocysteinemia (accumulation of homocysteine) which is a risk factor for thrombosis [8]. Our patient presented an ischemic stroke three months after the vitamin B12 administration."
https://doi.org/10.30574/wjarr.2023.18.3.1095

Essential thrombocythemia masked by vitamin B 12 deficiency megaloblastic anemia: A case report

https://doi.org/10.30574/wjarr.2023.18.3.1095

The blood test showed I have over 2,000 mg of B12, which isn't surprising, as I had taken that amount of B12 with usual morning meds, a few hours earlier. Happily: Adding a fourth day of two Anagrelide, with one Anagrelide on other days of the week, has in one month reduced platelets from 582 to around 512. My digestion is normal and my red blood cells are normal instead of too low. Medicated blood pressure is normal. Difficult to be sure of cause and effect. My blood specialist says I'm doing "great" and should continue doing what I'm doing.