Which lifestyle choice can deplete the body's antioxidant levels?

The choice of smoking as the correct answer is based on the fact that smoking introduces a variety of harmful substances into the body, including free radicals, which are unstable molecules that can cause oxidative stress. This oxidative stress depletes the body’s antioxidant levels, as antioxidants are used up to neutralize these free radicals and protect the cells and tissues from damage.

In contrast, regular physical activity, adequate hydration, and maintaining a balanced diet are all considered healthy lifestyle choices that can actually promote the body’s antioxidant levels. Regular exercise has been shown to boost the production of endogenous antioxidants, hydration supports overall health and physiological functions, and a balanced diet rich in fruits and vegetables provides essential vitamins and minerals that are crucial for antioxidant defense. Thus, while smoking can lead to a decrease in the body's ability to fight oxidative stress, the other options support or enhance antioxidant levels.