1. Caffeine Dehydrates You
Let’s start these myths off on a positive note: Your morning cup of coffee can boost your hydration levels. While experts have long believed that caffeine, like that contained in coffee, acts as a diuretic to dehydrate the body, recent research published in PLOS ONE found that in people who drink up to four cups of caffeinated Joe per day, coffee is just as hydrating as H2O.
It's important to remember that hydration levels tend to be lowest in the morning, since you spend all night sleeping, not drinking. So if what you want first thing in the morning is a cup (or two) of coffee, go for it, says registered dietitian and board-certified sports dietitian Georgie Fear, author of “Lean Habits for Lifelong Weight Loss.”
2. You Need to Drink Eight Glasses of Water Per Day
There are multiple reasons why this well-meaning guideline falls short of guaranteeing good hydration. For starters, every person’s hydration needs are unique. Age and sex are two big factors: The National Academies of Sciences, Engineering, and Medicine recommends that while men and women ages 19 to 30 consume 15.6 cups and 11.4 cups of water per day, respectively, toddlers need as little as 4 cups per day. Climate, exercise as well as pregnancy and lactation all move the needle, too.
Here’s how popular functional waters, which promise benefits beyond hydration, stack up.
But this next part is also important: All of that water doesn’t have to come in beverage form. According to the National Academies, roughly 20 percent of the average adult’s water consumption actually comes from food. “If you eat more of a plant-based diet, it could contribute even more,” says registered dietitian Betsy Opyt, creator of Betsy’s Best. She notes that fruits and veggies such as watermelon, cucumbers, celery and star fruit are more than 90 percent water.
3. As Long as You Aren’t Thirsty, You’re Well-Hydrated
Think of thirst like sunburns – it doesn’t pop up until it’s too late. “People are typically dehydrated by about 2 to 3 percent of their body weight, which is enough to impact physical and mental performance, before thirst kicks in,” explains registered dietitian and board-certified sports dietitian Marie Spano. Plus, the body’s biological thirst mechanisms tend to become even more faulty with age, so it’s especially important for older adults not to count on thirst as a hydration gauge.
While many experts like to use the guide, “as long as your urine is pale yellow or clear, you’re well hydrated,” it’s important to remember that everything from medications and supplements to the foods you eat can influence your urine color, Spano notes. Her bathroom rule: If you need to pee once every few hours, you’re likely well-hydrated.
4. The More Water You Can Drink in a Day, the Better
“If you really push the fluids, you can dilute the concentrations of electrolytes in your blood." “Hyponatremia, or low blood levels of sodium, is a dangerous condition, even life-threatening. Some unfortunate deaths have occurred as a result of drinking a gallon of water as part of a contest, or among marathoners who drank too much water without taking in any electrolytes.”
While, fortunately, these tragedies are uncommon, the National Academies similarly notes that acute water toxicity can occur by drinking excessively more fluid than your body can excrete in a given timeframe – about 3 to 4 cups per hour.
5. Sports Drinks Are Always Superior to Water
Sports drinks are great for their electrolytes (think: calcium, magnesium, potassium, sodium, phosphate and chloride), helping to prevent issues such as fatigue, nausea, headache, impaired muscle function as well as severe hyponatremia – all of which are possible when you’re sweating out electrolytes and drinking plain ’ol water. Meanwhile, they also contain simple sugars and calories that are meant to keep the body primed with energy when you’re in the middle of a long endurance workout.
However, a quick jog around the block doesn’t qualify. “Unless you’re exercising for more than 90 minutes or in extremely hot and humid conditions, water will do,” says Fear, noting that downing sports drinks when you really don’t need them is why many people who take up running gain, rather than lose, weight.