Maintaining Adequate Hydration

Looking around one might think that there is an epidemic of dehydration plaguing Americans, who tote drinks with them to all locales--cars and strollers armed with cups holders, hydration stations every mile of a running race, exercise belts studded with water bottles marketed to the recreational runner. It seems we might all shrivel up and dehydrate without this. 

We all know that drinking sugary soda is bad for us and has helped lead to the current obesity epidemic.  We have been led to believe that incessant water drinking is healthy, but how much and what does one really need to drink to feel good and prevent problems?

As summer approaches in Hotlanta, my home, I’ve become interested in learning more of the specifics of what constitutes healthy fluid consumption. In my practice I see patients both who over-hydrate and those who under-hydrate, each of which can contribute to medical morbidity.

Humans and other animals are adapted to have finely tuned physiologic mechanisms to protect against dehydration. The perceived result of these mechanisms is thirst.  Studies have shown that as we age our thirst mechanism becomes less effective, making older adults particularly sensitive to dehydration.  According to tables of normative water requirements for men and women by age and energy expenditure, an average middle aged man  should consume about 3.7 liters of fluid daily (125 oz. or 15 cups). An average middle aged woman should consume about 2.7 liters of fluid daily (91 oz. or 11 cups). Of course, fluid requirements also depend on fluid losses through sweating, which can range from .3 L/hour to 2 L/hour. I found this reference Water, Hydration and Health to be very informative.

What constitutes healthy fluid replenishment in the context of exercise? The American Academy of Sports Medicine recommends that athletes pre-hydrate 4 hours prior to physical activity with 2-3 mL per pound of body weight. For me, at 130 pounds, that’s 325 ml of liquid (11 oz., or about a cup and a half). For a man weighing 200 pounds that’s about 500 ml of liquid (17 oz., or about 2 cups).  Here’s a very good brochure on the subject:

During exercise, adequate hydration is defined as preventing a loss of more than 2% of one’s body weight. Again, using myself as an example at 130 pounds, that’s about 2.5 lbs. I know my usual “hydrated” weight, and typically weigh myself after exercise and before showering so it’s fairly easy to monitor my fluid loss. 

According to recent guidelines, rapid and complete recovery from excessive dehydration can be accomplished by drinking at least 16-24 oz. (450-675 mL) of fluid for every pound (0.5 kg) of body weight lost during exercise. What’s the best liquid to consume? At least some of one’s rehydration should include fluid with electrolytes---sodium and potassium. In addition, carbohydrate (sugar) in fluid actually helps to replenish glycogen stores, and has been found to improve athletic performance. Of course, for those who are trying to lose weight through physical activity, consuming beverages with carbohydrates also contributes calories, so one needs to be careful about overdoing it with sugary beverages, including sports drinks like Gatorade or PowerAde. My personal practice is to consume one bottle or can of salty beverage (500 mL) and approximately 16 oz. of water after a summer work-out of 45 minute duration (my most common exercise duration). Drinking a sports drink 30-45 minutes into a race that’s destined to last more than 60-90 minutes may enhance performance, followed by drinking water as one is able every 15-30 minutes thereafter. One of my personal favorite beverages with which to help rehydrate with is V-8 or tomato juice, which is loaded with sodium and potassium, though the carbohydrate content is less than Gatorade or PowerAde. I typically drink this along with my usual 2-3 cups of water after a vigorous 60 minute work-out in the summer.

The risk of excessive water drinking is hyponatremia, which is known to occur in athletes who exercise in the heat and then re-hydrate with large amounts of water without salt or electrolyte content quickly. In my office I also see hyponatremia as a problem for some patients who consume large amounts of water for health reasons or weight loss (“psychogenic polydipsia”), or who are on diuretics, which cause loss of sodium. 

The Institute of Medicine recommends the following composition of sports drinks for prolonged (>60 minutes) physical activity in hot weather: 20-30 meq/L of sodium, 2-5mEq/L potassium, and 5-10% carb (>8% may delay gastric emptying).

Here is a comparison of the nutritional content of various drinks along with an approximate range for the electrolyte content of sweat (which can vary considerably in sodium content).  Something interesting that I learned through reading on this subject is that muscle cramps in athletes seem to correlate more with sodium loss than potassium loss. As you can see, Gatorade does approximate the electrolyte content of sweat.

Nutritional Content per : 1 cup, 8 oz.,  237 ml	Gatorade	Chocolate Milk	V-8	ZICO: Coconut Water	Sweat (estimate)
Sodium (mg)	104.4 mg	152.5 mg	640 mg	64 mg	~100-300 mg
Potassium (mg)	30 mg	425 mg	445 mg	471.36 mg	~40-60 mg
Carb (gm)	14 gm	26 gm	9.7 gm	10.72 gm
Protein (gm)	0	8 gm	0	0
Fat	0	2.5 gm	0	0

My conclusion--while the contrarian in me used poke fun at the ever water-toting health nut, I’ve now become a believer. Personally, I’ve probably been running on the dry side.

 

Balancing the risks and benefits of endurance exercise

The health benefits of exercise are well-established.  A recent study published in the Journal of the American College of Cardiology showed that one’s fitness level, as measured a person’s one mile run speed, compared to other cardiovascular risk factors, was the best single predictor of heart attack risk and life span. Studies have shown that regular exercise reduces one’s risk of obesity, diabetes, and hypertension.  Exercise has been shown to benefit mood and alleviate the symptoms of depression.   On a cellular level, telomere length, a marker of mitochondrial health, has been shown to be improved in those who exercise.  Consequently, getting people to exercise more has been adopted as a top strategy of health promotion. 

I am an exercise zealot.  Growing up I swam and dove competitively.  As an 18 year old, fearful of the freshman fifteen, I took on running, and have been hooked ever since.   In my middle age, wanting to cross train more because of increasingly achy joints and muscles, I have ventured into bicycling.  We talk much of the health benefits of these sports, but what of the risks?  While exercise long term may be good, do the risks of injury and accident offset the potential for long term benefit and actually increase health care utilization?  Consider three of the most commonly practiced forms of exercise:  running, swimming and cycling.

As a sport, running carries the risk of overuse syndromes: runner’s knee (patella femoral syndrome), iliotibial band syndrome, plantar fasciitis, stress fractures, piriformis syndrome, and Achilles tendinitis, to name a few. Female runners may suffer from the Female Athlete Triad—amenorrhea, bone loss and disordered eating.   Marathon running is known to be associated with low bone density and may also increase oxidative stress.  Whether or not running is the cause of osteoarthritis of the knee is somewhat controversial.  MRI demonstrates knee abnormalities in marathon runners that are not seen non-runners.  Clearly in those already affected by arthritis or prior injury, running makes the condition worse.  Approximately 1 in 3 runners are injured per year of running.  

On the other hand swimming, as a sport, is relatively safe, unless of course you drown.  It turns out that 36% of swimmers who drown in Georgia are intoxicated while swimming—alcohol and swimming don’t mix. Otherwise, shoulder bursitis and rotator tendinitis are the most common swimming related injuries.

In my view, of the three sports, biking may be most risky. Approximately one in three bikers has an accident per three years of biking.  The annual rate of accident for regular bikers is about one and ten (less than running). However, in comparison with the debilitating overuse injuries of running, biking carries a more profound risk of serious injury and death.  Studies show that the risk of head injury and upper facial fractures may be reduced by 60 to 70% with helmet use.  Legislation requiring bike helmet use has increased compliance with this health-promoting behavior.   There’s also the threat of pudendal nerve injury and for men, erectile dysfunction.  A recent study showed 94% of asymptomatic male, mountain bikers had evidence of scrotal abnormality on ultrasound, presumed the result of chronic repeated microtrauma, compared to 16% of non-bikers who had abnormalities.  Avid bikers will tell you that proper seat ergonomics and padded shorts help reduced these risks of saddle injury.

In a triathalon a couple of years ago I took a hair pin turn too quickly, driving off the road into a grassy embankment.  Fortunately, I sustained only minor abrasions and was able to keep riding.  Others are faced with more serious injury.  Recently, in a tragic accident, a male physician biking across a bridge in Charleston, South Carolina was killed by a passing truck that hit him throwing him off the bridge. Bikes are no match for cars, and it's a drivers world that we live in unfortunately.

I exercise because I like getting outdoors and being active.  It gives me a sense of well-being, improves my mood, makes me more confident about my physique, and seems to keep my weight in check.  I hope it will result in further health benefits down the road.  The positive data seems good, however when prescribing exercise to promote health it’s important to weigh the balance of risk and benefit.   Despite popular notions, the practices of stretching and cross-training have not been convincingly demonstrated to reduce injury. Given the physical diversity of those who exercise and the lack of good data on what helps prevent injury, a common sense approach seems reasonable. Of course, as I write this blog with my calf resting on a bag of ice, talking common sense to an exercise enthusiast can be a challenge.

Is Distance Running Really Good For Your Heart?

By guest blogger: Kreton Mavromatis, MD, Assistant Professor of Medicine, Emory University, Director of Cardiac Catheterization, Atlanta VA Hospital
It's Sunday morning, July 4^th and I have just returned from running a 10K race and I am feeling good.  I run approximately 3 or 4 days per week, and I run a race or two, including a half-marathon, each year, mainly to serve as a training goal. My motivation for running is primarily so that I can afford to eat more food, my favorite daily activity. However, as a cardiologist, seeing people with heart attacks from occluded coronary arteries day-in and day-out, I have always believed that running (and exercise in general) is good for my vascular health. After all, doesn't running lower blood pressure and cholesterol, and haven't studies shown that people who exercise more live longer? In fact, prospective epidemiological studies have suggested a dose related effect, implying more exercise of greater intensity is better.
To my dismay, however, several recent studies have suggested that running may not be good for my heart or arteries after all. Mohlenkamp et al showed that 108 apparently healthy marathon runners had more coronary artery calcium (which is found in coronary artery atherosclerosis) than patients matched for age and Framingham risk score (a commonly used measure of a person's risk for cardiovascular disease based on their risk factor profile). Furthermore, they showed that the amount of coronary artery calcium, as well as the number of marathons run, was directly associated with myocardial (heart) damage, which was detected in 12% of the marathon runners. Finally, four of the runners had cardiovascular "events" over the next 2 years, all of whom had high levels of coronary artery calcium. Similarly, Schwartz et al. showed that 25 marathoners had more coronary artery plaque than 25 non-marathoners who had similar ages, blood pressure and cholesterol levels.
These studies are far from conclusive. The marathon runners may have had more predisposition to coronary artery disease than the non-runners despite similar Framingham risk scores, perhaps due to prior lifestyle differences (i.e. smoking, diet) or a more extensive family history of such disease. On the other hand, there are plausible mechanisms by which running could increase vascular disease. Intensive exercise is well-known to increase oxidative stress and inflammation, which are fundamental to the development of coronary artery disease.
Runners like me like to believe that running is good for our heart and blood vessels, based on the principle of "use it or lose it". However, maybe the cardiovascular system is more like a car (and just about everything else), the more "mileage" it has, the more likely it is to break down.

Is Exercise the Fountain of Youth?

For my kick off blog I have chosen discuss exercise. As an avid runner, or so I label myself, I've run 15 to 30 miles a week for over twenty years. I pride myself on remaining injury-free throughout those twenty years and attribute that to a combination of moderation, cross-training and good luck.

The 2008 Physical Activity Guidelines for Americans were developed by the Department of Health and Human Services and are endorsed by the CDC citing the substantial evidence for the health benefits of regular physical activity. http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html#

These recommendations suggest the following minimum requirements for adults:

1. Exercise of moderate-intensity (i.e., brisk walking) for 30 minutes on most days of the week for a total of 150 minutes per week.
OR
2. Exercise of vigorous intensity (i.e., running) for shorter duration three to four days a week, for a total of 75 minutes a week.
AND
3. Strength training on two non-consecutive days of the week using all major muscle groups.

Furthermore, there is evidence that more exercise of higher intensity is better, and that some exercise is better than none, particularly in elderly adults with chronic illness who are limited physically. Despite popular trends, stretching has not yet made it into the formal guidelines for physical activity.

Sunday's New York Times Magazine reported an interesting study, finding that middle-aged adults who exercise vigorously (ran 50 miles a week) were youthful at a cellular level. The study looked at telomeres, an intracellular marker for cell age. With age telomeres become shorter, and eventually cell death occurs. Middle-aged exercisers had telomeres that were significantly longer than their sedentary counterparts and only slightly shorter than those of exercising younger study subjects. http://well.blogs.nytimes.com/2010/01/27/phys-ed-how-exercising-keeps-your-cells-young/?ref=magazine

The January 25th issue of the Archives of Internal Medicine published several more studies demonstrating the benefits of physical activity in middle-aged and elderly adults. One reported on the cognitive benefits of strength training (compared with balance and tone training) in the elderly. The other reported on a cohort from the Nurse's Health Study demonstrating a positive correlation of exercise in mid-life with "successful" living at age 70 and beyond (defined as being free of chronic illness).

I am heartened to see many vigorous older adults at my local YMCA. They are clearly engaged and having fun. To me, the psychological benefits of physical activity have always been paramount and equal in importance to its physical effects.

Is physical activity the panacea of old age? Is there reason to be skeptical? How much is enough, and what should we be recommending?