Toxic Dose of Water PDF - 2017

# A Toxic Dose of Water ## How Much is Too Much? By Raima Larter **0** NE HOT AUGUST DAY IN 2014, THE FOOTBALL TEAM AT DOUGLAS COUNTY HIGH SCHOOL NEAR ATLANTA, GEORGIA, WAS FINISHING PRACTICE. Seventeen-year-old Zyrees Oliver was overcome by the heat and collapsed. He was taken to the hospital wh...

# A Toxic Dose of Water ## How Much is Too Much? By Raima Larter **0** NE HOT AUGUST DAY IN 2014, THE FOOTBALL TEAM AT DOUGLAS COUNTY HIGH SCHOOL NEAR ATLANTA, GEORGIA, WAS FINISHING PRACTICE. Seventeen-year-old Zyrees Oliver was overcome by the heat and collapsed. He was taken to the hospital where, several days later, he died. Doctors determined that his death was not a result of dehydration or heat stroke, as you may expect - he died because he had consumed too much water. Can drinking too much water really kill someone? Doctors explained to Zyrees's family that his brain swelled because of excess water in his body. His family confirmed that Zyrees had, indeed, consumed a lot of water - two gallons, in fact, and two additional gallons of Gatorade®, which is mostly water. Zyrees's condition is known as hyponatremia, which more commonly affects marathon runners. In 2002, the forecast for the Boston Marathon was warm. Runner Cynthia Lucero prepared by drinking water before the race, and she drank Gatorade® while running - she passed out around mile 22. She was immediately transported to the hospital, and died three days later from hyponatremia. We are warned repeatedly of the dangers of dehydration and told to stay hydrated in hot weather, especially while doing vigorous activities. Zyrees and Cynthia took efforts to drink fluids during vigorous activity. So why did they die? Let's look a little deeper. ## What happened? Water is found everywhere in our bodies, both inside our cells (intracellular) and outside them (extra-cellular), including in blood. Cells shrink if the amount of water inside the cell is too low. They can swell and burst if the amount of water is too high. The water content of a cell is dependent on the total salt, or electrolyte, concentration. Electrolyte balance is a key factor in keeping our cells healthy and functioning normally. Several common electrolytes are found in the body. Each serves a specific and important role, but most are in some part responsible for maintaining the balance of water between the intracellular and extracellular environments. In the extracellular compartments, water is found between the cells in tissue and blood. For the average person, about two-thirds of the body's water is intracellular, but water is constantly exchanged between the intracellular and extracellular cells. This process is critically important for hydration, nerve impulses, muscle function (including the heart), and pH level. | Ion | Cell (M) | Blood (M) | |---|---|---| | K+ | 0.139 | 0.004 | | Na+ | 0.012 | 0.145 | | Cl | 0.004 | 0.116 | | HCO3 | 0.012 | 0.029 | | X- (proteins) | 0.138 | 0.009 | | Mg2+ | 0.0008 | 0.0015 | | Ca2+ | <0.0000002 | 0.0018 | *Table 1. Typical ion concentrations in mammalian cells* *Source: Lodish, H.; Berk, A.; Zipursky, S.L. et al, Molecular Cell Biology, 4th ed.; W.H. Freeman: New York, 2000.* A salty solution is highly concentrated with electrolytes; a large number of ions are dissolved in a given amount of water. Chemists report concentration in molarity (M), which is the number of moles of solute (the substance being dissolved) divided by the volume of the resulting solution in liters. Typical concentrations of sodium, potassium, and other common ions in cells and in blood are shown in Table 1. By far, the most plentiful positive ion in the intracellular areas is potassium (K+), which is usually present at a concentration of about 0.139 M. This means that one liter of intracellular fluid contains 0.139 mole of K+. Na+ is the most plentiful ion in blood, with a concentration of 0.145 M. Electrolyte balance in the body refers to the ratio of ions inside cells to those in the extracellular regions. The cell membrane, a layer of lipid molecules, divides the outside of the cell from the inside and is a semipermeable barrier between these two regions. Water freely passes through the semi-permeable membrane, but movement of ions, such as sodium, potassium, and chloride, is partially blocked. Water moves between the inside of a cell and the surroundings by a process called osmosis, which describes water molecules moving from an area of low-solute concentration to an area of high-solute concentration (Fig. 1). Water is constantly moving in and out of cells. If the total amount of electrolytes is higher inside the cell, more water will enter the cell than will leave it. If the total amount of electrolytes is higher outside the cell, more water will leave than enter. The balance of water between the inside and outside of cells is achieved when the electrolyte concentration is equal inside and outside the cell. At this point, equilibrium has been established (Fig. 2). ## Hyponatremia occurs when this equilibrium is disrupted because the intracellular Na+ concentration is higher than outside the cell (so much water has been consumed that the concentration outside the cell has dropped significantly). The cells respond to this change by moving water from outside the cells (more dilute solution) to inside the cells (more concentrated solution). When water moves from outside to inside the cells during hyponatremia, a new equilibrium is established. In this equilibrium, the electrolyte concentration is equal inside and outside the cells, but the new electrolyte concentration is different from the value of the electrolyte concentration when equilibrium was initially established. When the amount of salt in the body falls due to excessive sweating, the body tries to keep the normal Na+ level in blood between 0.135 M and 0.145 M. But when the sodium level in blood falls below 0.135 M, hyponatremia can occur. If an already severely dehydrated person drinks too much water, osmosis causes too much water to move into the cells’ interior. When hyponatremia occurs in brain cells, the swelling leads to increased pressure in the skull. This can cause a series of symptoms - including headache, nausea, seizures, respiratory arrest, and accumulation of fluid in the lung, which can be fatal if not immediately treated. This is probably what happened to Zyrees and Cynthia. To stay hydrated, they drank too much water. In doing so, they both diluted the Na+ concentration in their blood. Through osmosis, too much water rushed into their brain cells when the electrolyte balance in their bodies was stressed by excess water. All of this led to catastrophic consequences. We need water, but too much of it can be fatal. ## Moderation is key Sports drinks and electrolyte supplements are probably safe if consumed in moderate amounts, but do they help? The National Institutes of Health (NIH) says they do, and recommends that athletes use them to prevent hyponatremia. It seems that these athletes had the right idea, but went too far. It’s important to stay hydrated when exercising, particularly in hot weather. Many exercise professionals caution that thirst is not a good indicator of dehydration because we often become dehydrated before we become thirsty during exercise; however, others suggest that thirst is a good indicator for most athletes. Always drink water before, during, and after vigorous exercise, particularly in high heat or humidity, but don’t make the mistake Zyrees and Cynthia made of over-consuming. NIH recommends adults consume between 91 and 125 fluid ounces (2.7 to 3.7 liters) of water from beverages and food per day. However, individual needs depend on weight, age, activity level, and health conditions. NIH doesn’t specifically say how much water you should drink, but at the very least they explain that if you drink when you feel thirsty and have a beverage with meals, you should consume enough water to stay hydrated. It’s also better to choose water over high-calorie sweetened drinks. Recent studies link consumption of sweetened beverages to the obesity epidemic, metabolic syndrome, and fatty liver disease. Scientists conclude that reduced intake of sweetened beverages results in less weight gain and overall metabolic improvement. Stay attentive for signs of dehydration - nausea, muscle weakness, dizziness, and confusion are all signs that something is wrong. It could be dehydration, or it could be hyponatremia - the symptoms are identical, so get out of the heat and seek medical attention if you feel these symptoms coming on. ## Substances that separate into ions when dissolved in water are called electrolytes. The resulting solution conducts electricity, due to the mobility of the positive and negative ions.