Wikipedia says that you need around 120 micro-grams a day and is covered by usual meals.
One pill could easily contain 50 or even 100 times that amount, you can't eat enough to cover one pill a day (30 hours is already quite late)
But it could be those pills contain something else. After all, trying to resupply is a plot device that can be used 2 or 3 times in 24 episodes for example.