Hyponatremia (low sodium, or “water intoxication”) is a risk for runners with atrial fibrillation. It is certainly a risk for me and I believe I have experienced it a number of times in the past. Personally, I am much bigger than most marathoners (6’3” 205 lbs), and because of that and the atrial fibrillation, much slower – so I’m out there twice as long and sweating twice as much. Plus – over the years it has been drilled into all of us to make sure we drink enough water.
Ironman athletes, ultrarunners, and bigger runners are all at increased risk because we are simply out there for much longer periods of time. Women athletes tend to be at higher risk for hyponatremia – it has been found that women hydrate more during a race.
Drinking enough water is a good idea – but it needs to be accompanied by increasing salt intake.
Normal levels of sodium are about 135-145 mEq/L. Symptoms are likely to begin at 130 or lower and if you get below 120 the condition may become fatal. While there are a number of medical causes for hyponatremia marathon runners fall into the category of consuming too much water and not enough sodium, and sweating out valuable sodium. Think of the white dried salt on your temple or on your hydration pack straps after a long run.
Symptoms include bloating, headache, swelling (check to see if your ring or wristwatch seems to be getting tight), nausea, vomiting and eventually weakness, restlessness, confusion, and well . . . it just gets worse from there. It is particularly problematic for runners because some of the symptoms (headache, nausea, cramps, and dizziness) are the same symptoms for dehydration so the impulse is to drink more water – which of course makes it worse.
There is currently an ongoing study at the Houston Marathon involving volunteers who are followed closely, weighed, fluid intake measured, lab studies obtained, etc. The study found that runners with lowered sodium levels drank more water, retained more water than normal volunteers, and they lost more total sodium and had saltier sweat.
Runners who were dehydrated but not hyponatremic had higher heart and respiratory rates, felt worse, and had lower blood pressure than hyponatremic runners. The hyponatremic runners felt better, but had more nausea and bloating.
What can be done?
Drinking less water is sometimes recommended but it is difficult to do when you are used to drinking a lot of water while running. I’ve tried drinking less water during a marathon and frankly I think it made things worse. Also some runners can become hyponatremic without over-doing the water consumption.
Weighing yourself frequently along the course and looking for weight gain (water retention) has been recommended – YEAH RIGHT! How is this going to happen?
Personally I try to drink water with sodium supplemented (NUUN, GU Brew), and try grabbing some little pretzels at aid stations (if available); but some research suggests this might not always be helpful.
Fatigue? Really? Fatigue during a marathon – you don’t say? Isn’t that generally a part of the experience?
I don’t have a good answer. I know I’ve had problems with this – I’m clearly in the high risk category for hyponatremia. I also generally have particularly poor races if it is a warm day.
My interventions include
1.) Drinking enough water
2.) Electrolyte supplements in my water (NUUN, Gu Brew)
3.) Additional electrolyte supplementation (SaltStick caps, Endurolytes caps, little pretzels)
4.) Making sure I have a salty snack or meal after a race or long run
5.) Trying to dress so I’m a little cool rather than a little warm
I’d love to read your suggestions – please leave a comment if you have any experience with hyponatremia and suggestions as to how to avoid it.
Update (March 13, 2014):
I found this terrific article posted on Twitter by Dr. Larry Creswell. The key points are quoted below.
KEY POINTS
Most medical scientific organizations recommend low or moderate sodium diets to the general population in order to reduce the risk of high
blood pressure (hypertension).Regular physical activity reduces the risk of hypertension.
Athletes lose sodium in sweat during exercise. The amount of sodium that is lost during endurance exercise depends on the sweating rate and
the concentration of sodium in the sweat. In turn, sodium loss during exercise depends on individual factors, such as genetics, fitness and heat
acclimatization, as well as the type, intensity and duration of exercise and the external environment.Sodium ingestion by endurance athletes does not typically increase blood pressure, so low sodium diets are not recommended for individuals
who participate in long-term aerobic exercise.Sodium ingestion during or following endurance exercise will help to stimulate thirst and drinking as well as stimulate fluid retention by the kidney.
No athletes are immune to hypertension, so athletes should monitor their blood pressure as they do their general health. This is particularly
important for older athletes, athletes with a genetic predisposition to hypertension, stroke or other cardiovascular disease.
A Fib Runner - Distance Running and Mountain Biking With Atrial Fibrillation 