Any dangers of excess? Quick search shows:
Vitamin B1 Overdose Symptoms
The B vitamins all work together in a complex. Taking too much of a single B vitamin, such as vitamin B1, can cause an imbalance in the other B vitamins. In severe cases, the imbalance may cause deficiencies in the other B vitamins, which can cause a wide variety of symptoms. Deficiencies in several of the other B vitamins, such as B3, B6 and B12, can cause feelings of fatigue and tiredness, along with skin irritations and rashes. Deficiencies in B6 and B12 can lead to anemia, causing very pale skin and muscle weakness. Vitamin B12 deficiencies can also cause neurological symptoms, including numbness or tingling in the hands or feet.
The dosages recommended are essentially 600-1500 x the daily recommended dose. Do you think it could put the other b-vitamins out of whack in dosages this excessive as the site above warns? Marmite is touted to have roughly 1500%, about 23mg, maybe a food source is safer?
The only issue I am aware of from high dose vitamin B1 is increased need for potassium. Also, high doses may drop sugar levels so that is another thing to watch out for. Taking a B complex with the high dose B1 should address the issue with potential deficiencies in other B vitamins caused by B1.