A homeless patient with chronic alcoholism presents to clinic for confusion and ataxia. Which immediate nutritional intervention is highest priority and why?

Begin high-dose oral vitamin C to boost immune function and treat scurvy immediately, which is the most common cause of confusion in alcoholics.

Administer thiamine (B1) promptly before giving glucose, because alcoholics are at high risk for thiamine deficiency and glucose without thiamine can precipitate Wernicke encephalopathy.

Administer folic acid intramuscularly first, since folate replenishment will immediately reverse confusion and prevent ataxia in alcoholics.

Start high-dose niacin to correct pellagra, because pellagra is rapidly fatal and more common than thiamine deficiency in chronic alcoholism.