How much fluids do you really need?
It’s an old question about one of the most essential components of our diet, yet the answer is surprisingly debatable. Eight glasses a day? To satisfy thirst? So that your urine is clear?
Our body is 60 percent water, and water’s needed for every system and every cell to function. Water keeps our temperature stable, clears waste through our kidneys and urinary system, it pumps blood through our vessels – there’s no function in our body that doesn’t rely on water.
Since water is so critical to bodily functions our body maintains the same blood concentration over wide variations of fluid intake. It’s only when our body is missing significant amounts of water that we’ll see abnormalities in blood tests – and in our ability to function normally.
Dehydration, the state in which water is depleted to the point our body can’t maintain its normal functions is clearly dangerous.
But does being optimally hydrated make a difference? Do smaller variations in fluid intake – the kinds of variations we experience in everyday life and ones that are no way close to clinical dehydration – make a difference?
Although blood samples show little variation in concentration across wide differences of fluid intake, our urine becomes more and more concentrated the less fluid we have – that’s why urine might be a better marker of hydration. Studying urine samples suggests that half the kids in the US have highly concentrated urine, which suggests they’re not drinking much.
Mild fluid deficits, do they matter?
What are the health implications of milder fluid deficits?
A few studies suggest that mild dehydration affects short-term memory in school-aged kids, and on the other hand, when kids are given plenty of water, their memory and attention improves.
A new study, led by Naiman Khan and published in the Journal of Nutrition tests the effect of hydration on cognitive performance. 75 Kids aged 9-11 years from Illinois were tested in three conditions for 4 days each: They were drinking as usual (no intervention), were prescribed low water intake (16 oz. a day or about 2 glasses), or high water intake (84 oz. a day or about 10 glasses). On the fourth day of each condition urine was collected to measure its concentration and cognitive tests were performed to assess performance, thought flexibility and inhibition.
And the results: As expected, urine got less concentrated the more fluids the kids took in. Better…