Answer :Youre recalling the book Biomarkers: The 10 Determinants of Aging You Can Control by Tufts William Evans, PhD, and Irwin H. Rosenberg, MD. Dr. Rosenberg, who is the editor of the Health & Nutrition Letter, says, Yes, we still consider that exercise enhances the capacity for thermoregulation, which declines somewhat with age. As an older person, you have a reduced sensation of thirst and a lessened ability to sweat and shiver. While exercise probably wont alter your thirst mechanism for the better, it may still reduce your risk for dehydration injuries. Staying in shape, no matter what your age, helps you adjust to the heat. Thats because people who exercise have higher total body water content, sweat more when they work out in the heat, and lose fewer electrolytes.