Water and other drinkables: fluid needs

January 31, 4:49 PMNutrition ExaminerAnnie Kay

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Glug glug glug.  Photo

The recent kerfuffle wherein CSPI sued Coke for fraudulent claims for their VitaminWater products got me thinking about hydration, drinking and fluid needs. Beverage choices and the way those choices have been marketed to adults and children in this country has done serious damage to our collective nutritional status. Or have they? With water being described as one of the wonder diet aids of the decade, does making that choice really matter? Hmm. Sounds like more than one post.

Anyway, let's take a look at fluid needs. In another post I'll get into the ramifications of water vs. soda vs. VitaminWater vs. juice vs. whiskey sours.

How much do we need to drink each day?

There is an interesting little history around the accepted national recommendations for fluid. Interesting for science geeks like me, I should say. For decades the accepted fluid needs were described as "8X8", or eight 8 oz glasses of water each day, and if part of that were alcohol or coffee, you'd be sort of penalized for that by having to add half the fluid oz of your 'bad drink' amount to your grand total for the day. This is the recommendation that got us guzzling water as a national pastime.

In 2002 Heinz Valtin MD published a landmark review in the American Journal of Physiology calling into question the whole idea of the need for that much fluid, and suggesting that drinking when we are thirsty will, for most of us, be adequate for our needs. He found no supporting evidence for 8x8, and suggested that the dictum was possibly a misinterpretation of an earlier recommendation from the Food and Nutrition Board (FNB) of the National Research Council, which recommended 64-80 oz/day . The next sentence in the FNB's recommendation states that most of the requirement would come from food in a normal healthy diet, but Valtin things no one made it to that sentence. Valtin also argued that our body doesn't differentiate type of fluid (so yes, your whiskey sour WILL contribute to your fluid needs, though I don't recommend that!).  It quite rocked the boat in the nutrition world.

In 2004 the Institute of Medicine (IOM), the folks behind the (sort of) new Dietary Reference Intakes (DRI)s which replaced the Recommended Daily Allowances (RDA)s established evidence based recommendations for fluid. Here's what their report says:

• They agreed with Valtin that the vast majority of Americans can meet their fluid needs by drinking in response to thirst.
• Their report on fluid and electrolytes doesn't specify exact requirements for water, but set general recommendations of about 91 oz total water (from food and beverages) for women and about 125 oz for men.  No upper intake limit was set.
• About 80 percent of people's total water intake comes from drinking water and beverages -- including caffeinated beverages -- and the other 20 percent is derived from food. So, that translates to a general recommendation of drinking  about 9 glasses of water and other fluids (8oz glasses) daily for women and 121/2 glasses for men. Remember it includes all fluid drinks.
• Physical activity and heat exposure will increase water losses and therefore may raise daily fluid needs, as will illness.

So, it looks to me that the IOM lands not far from the original 8x8, though both the IOM and the Valtin review softened the need to think of these numbers as requirements - as 8x8 was.

Can you drink too much?

Valtin says fluid toxicity happens a lot, and can have detrimental long term effects, though his list includes things like contaminant toxicity and embarrassment from too much peeing, which I think can be managed(!). There have been deaths from water intoxication, though rare, in athletes, people on certain drugs (Ecstasy for example) and at risk patients.

What if you don't drink enough?

Dehydration is a serious medical condition. The Mayo Clinic offers these symptoms of dehydration, as well as guidelines for what to do about it.

Mild to moderate dehydration is likely to cause:

• Dry, sticky mouth
• Sleepiness or tiredness — children are likely to be less active than usual
• Thirst
• Decreased urine output — fewer than six wet diapers a day for infants and eight hours or more without urination for older children and teens
• Few or no tears when crying
• Muscle weakness
• Headache
• Dizziness or lightheadedness

Severe dehydration, a medical emergency, can cause:

• Extreme thirst
• Extreme fussiness or sleepiness in infants and children; irritability and confusion in adults
• Very dry mouth, skin and mucous membranes
• Lack of sweating
• Little or no urination — any urine that is produced will be dark yellow or amber
• Sunken eyes
• Shriveled and dry skin that lacks elasticity and doesn't "bounce back" when pinched into a fold
• In infants, sunken fontanels — the soft spots on the top of a baby's head
• Low blood pressure
• Rapid heartbeat
• Fever
• In the most serious cases, delirium or unconsciousness

The bottom line

When it comes to fluid, follow your thirst but know the symptoms of dehydration. If you've been pushing to get your 8X8 everyday but need to pee on the hour, try throttling back a bit. If you are an athlete, live in a warm climate or have certain health conditions, you may need more fluid at times. We can each learn the aspects of our lives that make us need a little more, or a little less daily fluid. If you have questions, a Registered Dietitian or other health professional can help.