Mature runners urged not to "die from ignorance"

21/08/2007

You're in your 50s or 60s or even your 70s, you’ve been training hard for your next marathon, and looked forward to this day for weeks. Donning your shorts and clutching your trusty water bottle to your side, you are ready to hit the tarmac. But have you considered the risk to your health if you let your sodium levels drop too low whilst running the marathon?

 

Marathon runners across the UK, including those of a more “mature” persuasion,  are being warned that they could be putting their lives at risk if they overdose on water while failing to maintain vital supplies of salt.

Hyponatraemia - defined as a low concentration of sodium in the blood - arises amongst runners during long races when large volumes of water are consumed without adequate sodium intake. The condition has emerged as an important cause of race-related death and life-threatening illness among marathon runners - yet the Government’s blanket advice says that six grammes a day is adequate for everyone.

The Salt Manufacturers’ Association (SMA) is currently writing to marathon organisers urging them to ensure that every runner is given adequate advice about hyponatraemia, which is believed to have been responsible for the death of a male runner in the London marathon this April as well as a number of deaths in other marathons.

Dr Simon Jenkins, in his book "Sports Science Handbook: The Essential Guide to Kinesiology, Sport and Exercise Science" writes: “Hyponatraemia is a condition in which there is low concentration of sodium in the blood plasma. Athletes who start already hyponatraemic from excessive drinking in the days or hours before the race are at particular risk of more severe hyponatraemia during the race, because less fluid is required to drop plasma sodium to dangerous levels.”

And Dr Emma Ross, from the Centre for Sports Medicine and Human Performance at Brunel University, reported that ‘recreational’ runners (general population rather than well-trained athletes) who participate in long-distance events lasting over four hours are the most ‘at-risk’ for hyponatraemia.

She said: “The current literature states that this is owing to over-hydration in the face of relatively low sweat rates, but also having a sodium content in sweat twofold higher than fit athletes. ‘Over-drinking’ is not the sole cause of exercise-induced hyponatraemia - indeed warning people not to drink too much during exercise could have catastrophic consequences in terms of dehydration and hyperthermia.

 

"Hyponatraemia will develop even without excess fluid intake, unless sweat sodium loss is adequately replaced (which could be by dietary salt during and after prolonged exercise)."

One study of marathon runners showed up to 13% suffering from some degree of hyponatraemia. Signs can include nausea, extreme fatigue, breathing difficulties, dizziness and coma. And other findings from a number of research projects involving marathon runners, cyclists and footballers, have already caused experts to question the UK government’s blanket advice on reducing salt intake and have drawn attention to one in six people who are ‘salty sweaters’ - in other words they sweat profusely and lose a lot of sodium when they do so.

Professor Ron Maughan, of Loughborough University, said: “Dehydration impairs performance in most events, and athletes should be well-hydrated before exercise. Sufficient fluid should be consumed during exercise to limit dehyration to less than about two per cent of body mass. During prolonged exercise the fluid should provide carbohydrate. Sodium should be included when sweat losses are high, especially if exercise lasts more than about two hours. Athletes should not drink so much that they gain weight during exercise. During recovery from exercise, rehydration should include replacement of both water and salts lost in sweat.”

Peter Sherratt, General Secretary of the SMA said: “Our Intersalt study involving 10,000 people from 52 countries, showed that almost everyone with free access to salt eats between six and 12 grammes of salt a day, and we in Britain are right in the middle at nine grammes. Perhaps the FSA and the Government are overlooking the fact that too little salt can lead to serious illness or death."

Dr Sandy Macnair, Medical Adviser to the Salt Manufacturers’ Association added: “During exercise and in the heat, we often turn to water to avoid dehydration, but that’s only part of the picture. Our bodies must also replace the sodium and other electrolytes lost through sweat, or we can lay ourselves open to hyponatraemia. Poor performance and cramps can follow a lack of salt, but the potentially life-threatening condition of hyponatraemia, which has affected several marathon runners, is caused by drinking excessive amounts of liquid. This dilutes the levels of salt in blood.

“I am surprised that the organisers of marathons don’t hand out salt replacement drinks at the mile posts rather than just water.”

Tips for fluid intake during exercise include using a sport drink containing sodium when high sweat losses are expected, and eating salty foods after training and competitions when salt losses are high.