The overdose mechanic including vitamins is ridiculous, to say the least. The whole point of vitamin junkie in even more traits IS to take multiple vitamins so your strength, fitness, sprinting xp is boosted, but this will kill you in Dynamic Traits due to overdose. This should be reworked, especially since you can't feasibly overdose on vitamins, at least not in a single day/week. From the Even More Traits wiki:

Vitamin Junkie -6
Taking vitamins grants a scaling buff to your Endurance gain and loss
Each Vitamin you take adds 1 to a hidden counter.
At levels 1-2 you have a 110% Endurance regen rate and 90% consumption rate. You also get a 40% bonus to Strength, Fitness, and Sprinting XP each tier lasts 360 in game minutes minutes at this stage
at levels 3-4 you have 120% Endurance regen rate and 80% consumption rate. 80% bonus to Strength, Fitness, and Sprinting each tier lasts 180 minutes
at levels 5-6 you have 130% Endurance regen rate and 70% consumption rate. 160% bonus to Strength, Fitness, and Sprinting each tier lasts 90 minutes
at levels 7 and above you have 140% endurance regen rate and 60% consumption rate. 320% bonus to Strength, Fitness, and Sprinting each tier lasts 45 minutes