Hyponatremia is also known as 'water intoxication' and is essentially the opposite of dehydration, with the subject having contained far too much fluid. For most beginner to intermediate runners, dehydration is going to be the main concern, rather than the issue of drinking too much. However, for a small minority of runners running long-distance events, hyponatremia can be a very real threat.
The following shocking account is but one of an increasing trend in endurance sports where participants, especially women, are suffering symptoms ranging from nausea to vomiting, collapse, seizures, hospitalization and even death:
Nearing the 22-mile mark of 2002’s Boston Marathon, 28-year-old Cynthia Lucero is starting to struggle. For all but the last 15min she had felt fine. Careful to stay as hydrated as possible she had walked while she drank at every aid station and while others struggled, she had taken Boston’s infamous Heartbreak Hill in her stride. But in the time that it took her to run the next 3km, Cynthia Lucero’s life unravelled.
At the 22-mile mark she was walking, felt nauseous and told a friend she must be dehydrated. Then in the next breath the friend watched as the walk turned to a wobble and she collapsed. Going into seizure, worried spectators called for an ambulance but by the time she arrived at a hospital Cynthia Lucero was in a coma. Two days later she died.
What is hyponatremia?
Hyponatremia, according to New Zealand's Dr Dale Speedy, who is the pioneer into research on the subject, 'is a lowering of sodium concentration in the blood due to water overload.'
Hyponatremia 'is a lowering of sodium concentration in the blood due to water overload.'
His explanation is that what happens is that people suffer from a 'waterlogging of the cells and brain'. This is essentially why people with hyponatremia suffer confusion, and in severe cases, seizures.
Speedy began studying hyponatremia as a direct result of his involvement as medical director of the Ironman New Zealand triathlon during the mid-1990s. In 1997 he put the entire field through medical screening and found that 18 per cent of the finishers were technically hyponatremic, although they showed no major symptoms. But a total of 16 people ended up in hospital!
What causes hyponatremia in runners
Studies indicate water overload and a sodium concentration scenario as the principal cause of hyponatremia. The woman who died in the Chicago Marathon in 2002 is reported to have drunk, 'gallons and gallons of water daily,' in the two weeks prior to the race. In his Ironman studies, Speedy came across some hyponatremia cases where athletes had drunk as much as 23 litres (6.08 gallons) of fluid during the race.
How to avoid hyponatremia
The key to avoiding hyponatremia is replacing fluids at the same rate as they are that they are being lost, and then balancing the dilution of the body’s sodium content by replacing it with drink containing sodium. Most people will on average use between 500ml (16.9oz) and 1000ml (33.8oz) of fluid an hour when exercising.
Who is most at risk from hyponatremia?
Female endurance athletes are considered to be the most at risk because they sweat less than men due to a smaller muscle mass and lower metabolism, so their fluid requirements are not as much as for men.
In general, however, hyponatremia appears to be a condition associated mostly with people who are competing for periods longer than four hours. A study of runners in the 2002 San Diego Marathon revealed no hyponatremia case finished in less than four hours. What this means for runners, is those most at risk are mid-pack marathoners and ultra-distance athletes, and especially women because they actually require less fluids than men.
How do I recognise hyponatremia?
The problem with hyponatremia is that the symptoms are very similar to dehydration, when the runner is in fact the exact opposite. In the 2002 Houston Marathon eight-time marathoner Kathy Schatte was one of four people who suffered hyponatremia, but it was presumed she was actually dehydrated, with almost tragic consequences.
The problem with hyponatremia is that the symptoms are very similar to dehydration...
Schatte had consumed plenty of fluid both before and during the event. In the fair conditions, she had taken in far more than her body required and finished the race suffering severe swelling in fingers and hands (basic water intoxication), severe cramps and vomiting. Presumed dehydrated she was put on an intravenous drip, which immediately sent her into seizure and eventually into a coma from which she didn't wake for two days.
Doctors said they had taken 8 litres of fluid out of her and that the fluid had got into her lungs. It was another three days until her sodium levels were deemed safe for her to be released and three weeks before she could stay awake long enough to go to work.
The early warning signs of hyponatremia are often subtle and may be similar to dehydration, with nausea, muscle cramps, disorientation, slurred speech and confusion. But in an article in Sports Medicine Digest, Dr E. Randy Eichner said symptoms more specific to hyponatremia were: 'bad headache, vomiting, bloating, puffiness from water retention (shoes tight, rings tight, wristband tight), confusion, and seizure.'
And yet, despite hyponatremia being much more problematic than dehydration, it is not commonly recognized or warned against. Dr John Hellemans isn't willing to take it so lightly, warning, 'as a health risk, overloading is much worse than underloading!' Symptoms of hyponatremia
- Fatigue, despite adequate fluid intake
- Loss of mental focus
- Low body temperature
- Weight gain during exercise
- Fitting and or or seizures
- Loss of consciousness
- In extreme cases, coma and or or death
However, despite the strong correlations between water overload, Speedy admits that there is a lot still unknown about what are the causes behind it all. Right now, for example, expert opinion is divided as to the relationship between overhydration and the loss of sodium via sweat. In an address to a sports nutrition conference in February 2001, Dr E. Randy Eichner promoted the role of salt loss to sweat as a contributing cause to hyponatremia.
'Studies have shown that athletes can lose two or more grams of salt per litre of sweat,' said Eichner, who is a Professor of Medicine at the University of Oklahoma Health Sciences Centre. 'If you consider that athletes may lose up to a litre or more of sweat each hour, you can see that over a long endurance event it is not unimaginable that an athlete could sweat out 30 or 40 grams of salt. Replacing this loss of sodium during an event is critical to performance and safety.'
Speedy thinks the real answer lies with finding out why the body cannot absorb or expel this excess fluid during exercise. John Hellemans, a sport medicine physician, coach and world champion triathlete tends to agree, saying: 'It seems to be tied to blood supply to the kidneys being shut down because blood flow is pulled away to supply the working muscles.'
Both Hellemans and Dale Speedy also wonder if it this absorption problem might have something to do with athletes adopting race day hydration regimes that they have not accustomed their body to in training.
Speedy’s extreme case of an Ironman athlete suffering hyponatremia after drinking 23 litres on race day is a classic example. With the average finisher clocking around 11 hours 30 minutes, this equates to a massive two litres of fluid per hour! Not only is that too much says Speedy, but, 'when athletes train usually they usually don't have the large amounts of fluid available to them like at races. So when they flood the body with fluid on race day perhaps the body can't cope.'