Which of the following is a symptom of dehydration that could lead to heat-related illnesses?

Headache is indeed a symptom of dehydration that can contribute to heat-related illnesses. When the body loses fluids and electrolytes, it can lead to decreased blood volume and increased body temperature, which can trigger headaches. Dehydration affects the brain's ability to function optimally, resulting in discomfort and pain.

In the context of heat-related illnesses, headaches can serve as an early warning sign indicating that the body is struggling to maintain its internal balance. Recognizing this symptom is crucial for taking preventive measures, such as rehydrating and cooling down, before more severe heat-related conditions develop.

Understanding the relationship between dehydration and heat-related symptoms is essential, especially when training or working in hot environments where maintaining proper hydration is vital for overall health and safety.