Which of the following is an early sign of dehydration?

Dizziness is considered an early sign of dehydration due to its relationship with fluid balance in the body. When a person is dehydrated, the body loses fluids and electrolytes, which can reduce blood volume and affect blood circulation to the brain. This reduced circulation can lead to feelings of dizziness or lightheadedness, especially when standing or engaging in physical activity. Recognizing dizziness as an early sign allows for prompt action to rehydrate and restore fluid balance, preventing more severe dehydration symptoms from developing.

The other options, while associated with dehydration, are more likely to occur as dehydration progresses or becomes more severe. Headaches can occur due to insufficient hydration and changes in blood volume but often develop after other signs. Muscle cramps are typically associated with electrolyte imbalances that can arise from prolonged dehydration rather than being an early sign. Nausea is also a potential symptom of dehydration but usually indicates a more advanced state of fluid loss or electrolyte imbalance. Understanding these distinctions can help individuals identify and respond to dehydration more effectively.