Peter Attia’s blog recently had an interesting article on the importance of hydrating well as we age. Research shows our thirst response becomes less reliable and we may not automatically drink enough based on thirst alone. So it is important to remember to hydrate more often. There is an opposite problem called hyponatremia, however, which can occur in people who drink a lot of fluid and also sweat a lot, but do not take in enough sodium. So it’s also important to watch your sodium intake, especially when exercising in the heat. This was first discovered by Professor Tim Noakes (reference here). It especially became a problem as more amateur athletes were doing events like marathons. This can make people sweat for several hours. Guidelines at the time were to drink on a schedule even when not thirsty, but adequate sodium intake was not emphasized enough.
I had a wake-up call about hydration in my late 50s. I went for a hard three-hour bike ride on a hot day. When I got home, I was headed for the shower, with my nice cold recovery drink in my hand, when I fainted and woke up on the floor. I was unhurt, fortunately, but have watched my hydration status on hot days ever since. I also take electrolyte tablets to prevent possible hyponatremia during long workouts.