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.

 

Should you be on cholesterol medication? How the new guidelines are different

Cardiovascular disease—including coronary atherosclerosis and cerebrovascular disease, remains the number one cause of mortality in the United States. One out of three people in this country will die of cardiovascular causes.  Although I can’t say that the other top causes of mortality are particularly attractive--cancer, chronic lung disease, accidents and dementia—premature cardiovascular death can certainly be very devastating and it makes sense to do our best to prevent it.

In November 2013 updated guidelines for the treatment of high cholesterol were released by the American College of Cardiology-American Heart Association.  These guidelines were the subject of significant controversy. In contrast to the previous guidelines from 2002, the current guidelines do not suggest treatment based primarily on numerical cholesterol targets. Rather, the guidelines stratify people according to determined cardiovascular risk and recommend either high intensity statin treatment, moderate intensity statin treatment, or no statin treatment. The guidelines do not support using other types of cholesterol-lowering drugs because at this point there is not good data to suggest that using other types of treatments is beneficial in terms of preventing actual cardiovascular outcomes (heart attack, stroke or cardiovascular death). This is despite the fact that there are treatments out there that do lower one’s cholesterol numbers.

How is cardiovascular risk determined? With the new guidelines, a new risk calculator was proposed. In my clinical practice in the past I’ve used the Framingham Risk Calculator and the Reynolds Risk Calculator . The new risk calculator released with the 2013 guidelines is a bit different. Some experts have suggested that it overestimates risk. With the new risk calculator, if one’s ten year risk of a cardiovascular event exceeds 7.5% then treatment with a statin is recommended.

The new guidelines divide people into the following groups of patients between ages 40 and 75 years who are in need of treatment with statins, or so called “statin benefit groups.”

·         Those with LDL over 190mg/dL (high intensity statin treatment is recommended)

·         Those with a ten year risk of >7.5% (moderate intensity statin treatment is recommended)

·         Those with established cardiovascular disease (high intensity statin treatment is recommended)

·         Those with diabetes, in which 10 year risk is >7.5% (high intensity statin treatment is recommended)

·         Those with diabetes, in which 10 year risk is <7 .5="" font="" intensity="" moderate="" statin="">treatment is recommended)

Click here to calculate your risk. What qualifies as high intensity statin treatment? LDL lowering of 50% or greater. What is moderate intensity statin treatment? LDL lowering of 30-50%.

The guidelines suggest that particular statins may be better than others at achieving these goals and good outcomes: atorvastatin, simvastatin, and rosuvastatin.  Other statins are typically used when patients experience unwanted side effects, like muscle pain.

How are things different with the new guidelines?

Let’s take an example.    A 71 year old white female, non-smoker, non-diabetic, with a history of hypertension, asked me whether or not she should be treated for high cholesterol.  She is concerned about her risk of heart disease, as her mother had a stroke in her 60s and then sudden death, presumed cardiovascular, at age 83. My patient’s most recent total cholesterol level was 204 mg/dL with an LDL level of 121 mg/dL and an HDL level of 64 mg/dL.  A couple of years ago I calculated her Framingham Risk score, which is 6% with these risk factors. This represents low to intermediate risk. To get further information I also ordered a coronary calcium score, which was found to be zero.  Last year, based on these numbers and the older guidelines, I recommended against treatment with a statin.  However, now, based on the new risk assessment tool, the same patient has a ten year risk of 16%.  With the new guidelines she would unequivocally qualify for moderate dose statin.   At this point, I am not exactly sure what to do with the coronary calcium score, which probably projects that her risk is lower than the 16% that the new equation came up with.  Nonetheless, I am not sure that coronary calcium scoring entirely predicts all cardiovascular risk—for example risk related to small vessel disease and stroke, so perhaps she should receive treatment.  Low dose, statin treatment might be a good compromise here.

Interestingly, based on this new risk calculator virtually every 71 year old, even with optimal risk factors, would qualify for treatment with a statin.  Herein lies the controversy with this tool.

Nonetheless, my own view of the new guidelines is mostly favorable. To me it simplifies things based on what we know from numerous well designed studies. Treatment, with an emphasis on statins, is based on risk projection and less attention is paid to absolute numbers.  I hope that the next decade will continue to bring more a nuanced understanding of risk.