water and brain function

Water and the Brain

I’ve had water on my mind lately (which is not the same as, but does not preclude, water on the brain).
Anyway, ever since my sister-in-law’s mother was taken to the doctor with signs of Alzheimer’s and discovered to have nothing but dehydration, I’ve been meaning to read up on how exactly the lack of water hinders brain function.

Here’s what I found about dehydration and the aging brain:
Not much—unless you count articles on websites trying to sell water filtration systems.
The fact that water makes up 70-80% of a nerve cell and transports both nutrients and wastes from neurons means it is essential for proper brain function all through life. That’s a given. What’s not a given is how much a brain has to be depleted of water to affect cognition.
Rigorous research on the topic of the brain and dehydration is limited. Even the “standard facts” about the body and water are all over the place: babies come out of the womb composed of 90% water; no, 78%; no, make that 70%. In adults, the proportion is 60% water for males and 55% for females. The consensus is 50-60% for adults in general. The brain is 60% water; nay, 90%. Whatever.
As for how much water you need to drink on a daily basis to be properly hydrated, oy, there is no consensus. For years I’ve been hearing “8 cups a day.” No allowance for a sedentary life or for someone with a diet of fruits and vegetables (which are high in water content); no penalty for eating junk food (which would increase the need for the detoxifying properties of water) or for spending days cooped up near a wood stove.
One article quoted the Mayo Clinic as saying that “the average adult loses more than 80 ounces of water every day through sweating, breathing, and eliminating wastes,” and therefore you’d have to drink 10 cups of water/day to rehydrate. I searched for the quote on the Mayo Clinic site and didn’t find it. Instead, I found a recommendation for 6-8 cups of water per day.
Suppose you take the most conservative recommendation of 6 cups per day–do you follow that? I don’t think I’ve ever gone one whole week drinking that much per day.
It has been estimated that 75% of Americans are chronically dehydrated. OK, that figure is questioned. But it seems to be a fairly hard fact that “among people over 65, dehydration is one of the most frequent causes of hospitalization.”* Understandable: throw in a bit of incontinence, and fear of hydration soars. Also, some medications are diuretics, and after 50, the body loses kidney function and is less able to conserve fluids.*
But how bad is dehydration for your brain?
According to Lumosity, when your body lacks water,

brain cells and other neurons shrink and biochemical processes involved in cellular communication slow. A drop of as little as 1 to 2% of fluid levels can result in slower processing speeds, impaired short-term memory, tweaked visual tracking and deficits in attention. With proper hydration however, neurons work best and are capable of reacting faster.

But pinning down the exact link between hydration and cognitive function is tricky in the lab. From Hydration and Human Cognition:

Although adequate hydration is essential for optimal brain function, research addressing relationships between hydration status and human behavior and cognitive function is limited. The few published studies in this area are inconclusive and contradictory. The impact of variations in hydration status, which can be substantial as humans go about their daily activities, on brain function and behavior is not known and may impact quality of life.

From PubMed’s Hydration and Cognition: a Critical Review and Recommendations for Future Research: “The limited literature on the effects of dehydration on human cognitive function is contradictory and inconsistent.” The monkey wrench in research here is given as confounding factors:

Confounding factors, such as caffeine intake and the methods used to produce dehydration, need to be considered in the design and conduct of such studies. Inclusion of a positive control condition, such as alcohol intake, a hypnotic drug, or other treatments known to produce adverse changes in cognitive performance should be included in such studies. To the extent possible, efforts to blind both volunteers and investigators should be an important consideration in study design.

On the Mayo Clinic site, a Dr. Lette finds that “there’s no scientific evidence that drinking large amounts of water is good for one’s health.” The recommendation in this article is to drink when you’re thirsty, and that’s enough.
My question is, does the lack of scientific evidence mean there is no scientific proof or merely that there is no motivation to research the topic to obtain the evidencef? Who, after all, would fund research into water being fundamental to the health of the aging brain? Not the pharmaceutical industry. If you could avoid dementia by being continually hydrated, you wouldn’t need pills to fix dementia. Why would any self-respecting drug company fund that finding? And if it takes a lot of money to work through all the confounding factors, who’s going to pay for it?

The thing is, when the anecdote about my sister-in-law’s mother is not even rare, it makes me wonder how many cases of Alzheimer’s are checked for a history of dehydration. I don’t mean just the over-the-weekend kind of dehydration, but long-term, chronic shortage of water.
As with Mom. The list of things Mom was doing “right” for her aging brain is stellar: she was highly educated, spoke multiple languages, was given to prayer and meditation, was active in the community, etc., etc. Yet she succumbed to complete dementia in her early seventies! Could it all have been due to her severe distaste for water? I mean, she hated water–would gag if she drank it straight from the tap. Could her present dementia have been prevented by a regimen of 4+ cups of plain ole water daily?
I hate to look at the “what if” from Mom’s point of view, but for our generation and beyond, it needs a good deal more consideration than we’re giving it.
What do you think? Am I grasping at straws? (I suppose that’s OK as long as the straw is propped inside a nice glass of water, right?).

Water and Brain Function
Water in the Body”
You’re Not Demented, Just Dehydrated
Dehydration and Cognitive Performance
Hydration and Cognitive Function in Children
Nerve and Muscle Cells
Impaired cognitive function and mental performance in mild dehydration