The recommended daily limit for sodium intake is less than 2,300 milligrams
Marmite contains 490mg of salt per 8g serving, which could be approximately a teaspoon, but you can measure that yourself. This would bring the limit to 4 to 5 teaspoons a day to stay below the recommended intake.
The other component is Mono-Sodium Glutamate, which can lead to "increase in oxidative stress which could lead to alterations in the cardiovascular and renal function", per the NIH https://pmc.ncbi.nlm.nih.gov/articles/PMC9563186/
What would Americans know of the dangers of Marmite? I'm sure the British Heart Foundation have said that Marmite is perfectly safe at any amount. I'd provide facts, but I don't need to.
According to the linked research, for an 80kg person, problematic amount of Marmite from the MSG contents standpoint would firmly sit around 1,4kg daily consumption, in which case you will be also ingesting definitely lethal 140g of salt, and even worse, more than 11 standard size jars of Marmite.
My brother brought back Marmite for me to try when he was in the UK. I thought it was... weird, but it grew on me over time. Please start exporting this stuff, I miss it.