It's possible, but not likely in healthy people who let their thirst guide them. If your body retains water because of congestive heart failure, hypothyroidism, or long-term use of certain medications-notably non-steroidal anti-inflammatory drugs such as ibuprofen, ketoprofen, and naproxen-you need to be careful not to exceed recommended fluid intakes.
When you over hydrate, sodium concentrations can drop precipitously low, allowing water to leak into brain cells causing headache, confusion, personality changes, and even seizures, coma, or death. In the last few years athletes-particularly amateurs competing in marathons and other endurance events who take too literally the common advice to "drink as much as possible" have emerged as another risk group. To prevent over hydration, exercisers should make sure fluid consumption stays within the range of about 11/2 cups to 3 cups an hour.
How can I tell if I'm drinking enough?
The simplest way is to check your urine.
Scanty, strong, smelling, dark urine is a signal that you need to drink more. Color alone is not a good indicator because medications, vitamins, and diet can all affect color.
Do older people need to drink more?
No. The 10M recommendations for fluid intake are the same for all adults. A recent study conducted by geriatric and nutrition researchers from across them and England rejects the notion that older people should be encouraged to drink more because of chron ic dehydration. Using accurate measurements of fluid intake and urine output in 450 people ages 40 to 75, the researcher found that people of all ages vary widely in their intake, but the oldest group was as well hydrated as the youngest.
However, the sense of thirst does tend to diminish with age, increasing older people's risk of dehydration from heat or exercise. So they should be careful to drink a cup of water before and after exercise, plus another 4 ounces every 20 minutes or so during workouts-more if they're strenuous or in the heat.