Don’t Depend On Your Thirst Sensation To Guide Your Fluid Intake, Especially If You Are Older

DehydrationSkinTurgor

Skin that is pulled up and does not immediately return to its original state is a sign of dehydration. If the person is older, skin on the collarbone is a better indicator.

Another thing we shouldn’t depend on? The color of our urine. As we age, our ability to concentrate urine declines, which means our pee may be more dilute or lighter in color even when we’re not taking in adequate fluids.1,2 Of course, when you’re in the throes of dehydration, urine can be quite dark.

I’ve been reading about fluid balance as we age, and the issue of age-related dehydration. Some things I learned …

Thirst and fluid intake are distinct but, as you can imagine, related. Beginning in middle age, and becoming more acute in the 60s and beyond, we experience reduced thirst and reduced fluid intake – that’s involuntary fluid intake, or drinking without thinking about it. That’s the intake side of the equation. We also experience increased water loss. We lose more water through our skin (“insensibly” without feeling it), through breathing, and through urinating (more dilute urine) than we did when we were younger.2 All of this sets us up for dehydration as we age.

The moral of this story? As we age, we need to drink more than we did when we were young to maintain water balance.

This article …

Influence Of Age On Thirst And Fluid Intake, Medicine & Science in Sports & Exercise, September 2001

… begins by listing symptoms associated with not getting enough fluid:

The manifestations of thirst have been characterized as a combination of sensations that increase with dehydration and decrease with rehydration (restoration of fluid balance), including a dry, scratchy mouth and throat, chapped and dry lips, light-headedness, dizziness, tiredness, irritability, headache, loss of appetite, and feeling of an “empty stomach.”

Other symptoms of mild dehydration include:

  • Decreased urine output
  • Muscle cramps
  • Constipation
  • Low blood pressure
  • Rapid heartbeat or palpitations
  • Rapid breathing
  • Difficulty regulating body temperature, feeling too hot or too cold

That’s a lot of symptoms, isn’t it. Dehydration is not good.

That our thirst sensation declines has been documented. Why it declines is less understood. Complicating that understanding is that the maintenance of water balance is governed by several sensing mechanisms and several bodily functions involving several organs … the brain, the kidney, the endocrine system (e.g. we have a salt appetite that is activated by hormones, affecting both volume and osmolality of compartments), the skin, and others. Humans have evolved a complex system to prevent dehydration.

Here’s one mechanism that I found odd. In humans, the act of swallowing helps to regulate our fluid intake.3 If we haven’t swallowed enough, we’ll want more fluid, even if fluid was replenished by tube-feeding. And when we’ve swallowed enough, we don’t want to drink any more, even if the fluid we just drank was removed! This is from the 2001 Kenney paper up top:

Six subjects [were dehydrated] by light exercise in a warm environment on three different occasions. Rehydration involved one of three treatments. The first involved 75 min of ad libitum drinking. The second involved infusion of an identical volume directly into the stomach via a nasogastric (NG) tube, plus ad libitum drinking after 25 min. The third involved ad libitum drinking again, but with immediate withdrawal of the fluid from the stomach. Reflex inhibition of thirst began within 5 min of rehydration in groups 1 and 3, but not in the infusion group. Ad libitum drinking without absorption (withdrawn with NG tube) resulted in only 15% more fluid intake than the ad libitum condition. These data demonstrate a clear role of esophageal metering in determining fluid intake during dipsogenic stimuli in humans.

Here’s some evidence for decreased thirst as we age, from Kenney and Chiu:

After a 24-hour period of restricted water intake that caused an equal weight loss in older and younger subjects, a group of healthy men 67–75 yr old were less thirsty and replaced less of the fluid deficit over the next 2 hours than did young controls.

In another study where a saline solution was infused, older men felt less thirsty and drank less than younger men.

And another:

During a 2-hour recovery period after each exercise session, young men replaced, on average, 80% of lost fluid drinking a carbohydrate-electrolyte drink, compared with 34% fractional fluid recovery in the 70-yr-old group.

They concluded:

When challenged by fluid deprivation, a hyperosmotic stimulus, hypovolemia, or exercise in a warm environment, older adults exhibit a decreased thirst sensation and reduced fluid intake. Acutely, fluid restoration is eventually effective, but restoration of fluid balance is slower. Longer term fluid intake (i.e., days to weeks) in response to repeated dehydrating stimuli also appears to be reduced, which may contribute to a relative inability to expand plasma volume. When age differences are noted in the physiological control systems associated with thirst and satiety, hypovolemia seems to be more closely associated with a decreased thirst sensation. Available evidence suggests that older men and women have a higher osmotic operating point for thirst sensation under normal daily conditions, and a diminished sensitivity to thirst and satiety reflexes arising from unloading (hypovolemia) and loading (hypervolemia) of baroreceptors, respectively.

DehydrationElderly3

Holy Water

Driving this point home … It takes less water to maintain water balance when we’re young than when we’re older. And we shouldn’t be relying on our thirst. Go back and look at the symptoms at the top of this page.

How much should older people be drinking? The Kenney paper cited a study which gave a normal range of beverage intake for 65 to 79 year olds, not counting fluid from food, as 1.6 to 2.4 liters a day. And…

In a Dutch survey of 539 healthy, independently living adults aged 65–79 yr, daily water intake averaged 2.15 L·d1 for men and 1.98 L·d1 for women.

These 2 liters a day are what the adults drank, not what was optimum, although the two may not differ. Older people should probably be drinking about 2 liters or 8 and a half cups of non-alcoholic fluid a day.

By the way, something I learned a while ago … water is produced in our cells when we burn carbohydrates, in the making of ATP. It is that water which helps to keep hibernating animals hydrated!

________
1 Electrolytes in the Aging, Advances in Chronic Kidney Disease, July 2010.
2 Increased Insensible Water Loss Contributes To Aging Related Dehydration, PLoS One, May 201. (We become less sensitive to antidiuretic hormone (ADH) or vasopressin. ADH’s job is to keep water in the body. Alcohol and caffeine both inhibit ADH causing us to pee more and lose more fluid.)
3 Regulation Of Fluid Intake In Dehydrated Humans: Role Of Oropharyngeal Stimulation, American Journal of Physiology, June 1997

15 thoughts on “Don’t Depend On Your Thirst Sensation To Guide Your Fluid Intake, Especially If You Are Older

  1. Bix Post author

    I’ve seen people on the web saying we should “listen to our body” and only drink when we are thirsty. For the elderly, this is a risky proposition.

    Reply
  2. bijin

    I did the test and I’m dehydrated. My problem is I’m out a lot and don’t want to look for bathrooms. I should stay home more times just to solve the problem. Seriously. I should stay put-finish knitting my scarf, practice my calligraphy and drink lots.
    I attended a health seminar a few months ago. One of the things the teacher said was 2 by 2….two quarts of water by 2 pm. But I’ve also read somewhere that the kind of water we drink also matters. We can drink tons and still be dehydrated.
    Have you heard of structured water?????
    I shared this article on FB for all my dehydrated friends! LOL

    Reply
    1. Bix Post author

      As we age, our skin loses elasticity, so the back of the hand will probably always not bounce back then, even if you are well hydrated. Skin on the forehead and collarbone is a better guide in older people.

      Looking for bathrooms! I hear you. I’m lucky if I drink 4 cups a day. Since I wrote this I’ve been trying. I like that “2 by 2.” I’m going to use it.

      Reply
  3. Bix Post author

    One thing that really surprised me … we can lose close to a liter a day, depending on our body size, just through water that escapes from our skin. And the older the skin, the more we lose. That’s not sweating, that’s “insensible” losses. That’s my 4 cups right there!

    Reply
  4. Marj

    This is amazing information. And I thought I was drinking more than enough water! Am definitely in the age category you mention (with cat, I might add). And had heard of the skin test on the hand which doesn’t look too great on mine, the collar bone was better. Nevertheless, will amp up my water intake in light of this post. 2 qts by 2 p.m., well, will try–being an early riser will definitely help with that.

    Reply
    1. Bix Post author

      With cat! I laughed.
      I tried yesterday. I think I made it to 5 cups, two of those were tea. I can ‘t be away from a bathroom for longer than an hour.

      Reply
  5. Melinda

    This is fascinating and shows why we need nutritionists like you–to explain not just what to do, but why you should do it. B/c I rise later than you (due to being up during the night with the cat, who has to be “assist-fed”), I doubt I’ll do 2 by 2, but I’ll try to up the amount. Damn, 2 liters is a lot! Does tea count too, or must it be water only?

    Reply
    1. Bix Post author

      If tea didn’t count I’d never make 5, let alone 8 cups.

      I have to say, it’s only been three days but my back-of-hand test has improved a bit. I think. Could be wishful thinking.

      Reply
  6. Melinda

    I’m curious about the current fad for “alkaline water”, which is starting to show up in stores. Supposed to be more “hydrating” than regular water. Here’s a study, though if you google alkaline water, you’ll see a lot of people question whether it’s bogus. But here’s one study: http://www.ncbi.nlm.nih.gov/pubmed/22844861
    And then there are the so-called “alkaline foods” that are supposed to help put our bodies into balance–things like veggies, fruits, some grains, etc. The idea’s been around for decades, but I have to say I don’t understand why what we tend to think of as more acidic foods like veggies & fruits tend to have an alkalinizing effect in the body. E.g., as here: http://www.acidalkalinediet.net/alkaline-foods.php

    Reply
    1. Bix Post author

      The acids in fruits and vegetables are weak acids, like citric acid, weak. Easy to neutralize. And the other components in plant foods, like potassium and magnesium, push blood to more alkaline, within a very tight range of course, 7.35 to 7.45 pH, tight.

      Animal foods are made up of more sulfur-based amino acids, which get metabolized to stronger acids. More difficult to neutralize, require more calcium and other buffers, lessening these minerals in bone.

      So, diets high in fish, cheese, eggs, chicken, red meat, and other animal foods tend to be more acid-forming than diets high in fruits and vegetables.

      Acid-forming diets are not good for the skeleton:

      Cross-cultural association between dietary animal protein and hip fracture: a hypothesis, Calcified Tissue International, 1992

      When female fracture rates derived from 34 published studies in 16 countries were regressed against estimates of dietary animal protein, a strong, positive association was found.

      Protein consumption and bone fractures in women, American Journal of Epidemiology, 1996

      Protein was associated with an increased risk of forearm fracture. … A similar increase in risk was observed for animal protein, but no association was found for consumption of vegetable protein. Women who consumed five or more servings of red meat per week also had a significantly increased risk of forearm fracture.

      Worldwide incidence of hip fracture in elderly women: relation to consumption of animal and vegetable foods, The Journals of Gerontology, 2000

      Hip fracture, a major health problem in elderly persons, varies in incidence among the populations of different countries and is directly related to animal protein intake, a finding that suggests that bone integrity is compromised by endogenous acid production consequent to the metabolism of animal proteins.

      Reply
  7. Melinda

    Wow, thanks for that GREAT explanation!!! Much appreciated–goes well with the WHO report–am so glad you posted on that too.

    Reply
  8. anrosh

    cooking in earthen vessels also decreases the acidity in the food – I read this somewhere, but can’t remember where. Added benefits : the flavors are sealed .in .

    Reply

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