I always encourage my patients to drink plenty of water. After all, 60% of your body weight is water.
Mild dehydration can lead to dry skin, headaches, constipation and fatigue. As it grows worse, you may develop a fever, low blood pressure or even heart problems. So staying hydrated is important.
But recent studies show that many people may be drinking too much water. So the question is how much water is enough?
When I was growing up, almost everyone said you should drink 8 glasses of water a day. It sounds like good advice, but it’s vague.
And how did they arrive at that magic number 8? Well, let’s look at water… some eye-opening research… and how much you really need.
In a now-famous study published in 2005, doctors looked at hundreds of Boston Marathon finishers.
Everyone “knows” running 26.2 miles puts you at a high risk for dehydration. So you’d expect to find a lot of dehydrated runners at the finish line.
But these runners provided the doctors with a surprise. Dehydration wasn’t the big problem. Instead, an amazing 13% of the runners they tested had a condition called “hyponatremia” – dangerously low levels of sodium.1
Hyponatremia can lead to hallucinations, muscle weakness, convulsions and even death. But it’s usually not caused by getting too little sodium. It’s usually caused by drinking too much water.
These runners, in an effort to avoid dehydration, had created the opposite problem. The excess water they drank diluted their sodium levels.
Over-estimating how much water you need seems to be a common problem. More than 4 out of 10 athletes responding to a recent British survey said they drank even when they weren’t thirsty.
In analyzing the overall results, the researchers discovered that most people don’t really know how much water they need… and tend to hold some very unscientific beliefs on the subject.2
Beliefs like drinking 8 glasses of water a day. As a recent article in the prestigious British Medical Journal pointed out, there really aren’t any studies to back up this folk wisdom.3 but I think there’s a good reason it’s stuck around for so long.
Through sweat, urine, moisture in your breath and other means, your body loses about 10-1/2 cups of water a day. Food provides about 20% of the average person’s need for water. What’s left is about 8 cups – or 64 ounces.
So drinking 8 8-ounce glasses should cover the average adult’s daily need for water. And other healthy beverages count towards that total. So a big glass of iced tea with lunch should fill about a quarter of your need.
Of course, the more you exercise the more water you’ll need. But 8 8-ounce glasses is a good baseline.
And that’s good to know as you get older… because mature adults often wind up dehydrated. And a research team in Australia has figured out why.
They discovered that thirsty young volunteers tended to drink about twice as much water as more mature subjects. But it wasn’t because they needed less.
A region of the brain – called the “mid-cingulate cortex” – helps determine how much water you need. In 21 – 30-year-olds, the cortex’s calculations were accurate in this study. But 65 – 70-year-old cortexes consistently miscalculated… by about half.4
Before middle age, you can probably just drink when you’re thirsty. As you get older, following “8 8-ounce glasses a day” is a good idea. If you exercise, you may need more. But as you’ve seen here, don’t over-do it.
Best Life Herbals Wellness Team
Best Life Herbals
1 Almond, C.S., et al, “Hyponatremia among runners in the Boston Marathon,” N Engl J Med. Apr 14, 2005;352(15):1550-6.
2 Winger, J.M., et al, “Beliefs about hydration and physiology drive drinking behaviours in runners,” Br J Sports Med 2011;45:646-649.
3 McCartney, M. “Waterlogged?” BMJ 2011;343:d4280.
4 Farrell, M.J., et al, “Effect of aging on regional cerebral blood flow responses associated with osmotic thirst and its satiation by water drinking: A PET study,” PNAS. Jan 8, 2008;105(1)382-387.