Dr John Briffa: Running on empty

Requests for sponsorship from those planning to run the London Marathon have made me aware that this sporting spectacular is not too far down the road. While I am enthusiastic about the health benefits of exercise, endurance activities such as marathon running are not without risk. For instance, while competitors in such events are advised to consume plenty of water, this can be overdone: in extreme circumstances, a surfeit of water may lead to lower-than-normal levels of sodium in the body that may cause complications such as convulsions, coma and even death. Scientific literature contains more than 250 reports of this syndrome, though under-reporting means that the actual numbers may well be far higher. The evidence suggests that individuals consuming an excess of water during exercise may be at risk of running to ground.

Although the replenishment of lost fluid during extended exercise is both widespread and accepted, this practice only came into vogue in the 1970s after being advocated as a way of staving off heat stroke. More latterly, studies have shown that dehydration can significantly impair performance. Perhaps as a result of this research, drinking during exercise has filtered through to other sports, too. Witness, for example, the recent phenomenon of professional football and rugby players taking slurps from sports bottles during breaks in play.

While there are good reasons to keep fluid levels topped up during exercise, the potential for low sodium in the system (the medical term for which is hyponatraemia) and the complications associated with it show that it is possible to have one too many for the road. During prolonged exercise, the body may lose significant amounts of sodium via sweat. Also, extended activities such as marathon running provide sufficient time for potentially harmful quantities of water to be imbibed. The risks associated with endurance exercise seem to have been compounded by commonly given advice that competitors should drink the maximum amount of fluid they can.

However, it may be safer to consume more moderate amounts of fluid during endurance events. This approach helps protect against hyponatraemia and reduces the risk that competitors will be slowed down by a surplus of water sloshing around the system. On the day of the event, quaffing about half a litre of water a couple of hours before the race will help ensure the body is well topped-up with fluid, but also gives ample time to shift any excess.

During the race, drinking 500 to 1,000ml (¼ to 1 litre) of water per hour should maintain a good level of hydration. Volumes at the upper end of this range will be appropriate for larger people, especially in the heat. Smaller bodies, especially in temperate climes, can make do with less. Drinking adequate, though not excessive, quantities of water during endurance exercise is best in the long run.

Nutrition news

Rates of type 2 diabetes, a condition characterised by elevated levels of sugar in the bloodstream, are expected to double over the next 10 years. An active lifestyle, perhaps coupled with an avoidance of too much in the way of refined sugar and grain-based carbohydrates in the diet, may help reduce the risk of this condition. Also, there is some evidence that higher levels of specific nutrients may confer a degree of protection from diabetes. In a recent Finnish study, for instance, people with the highest intake of vitamin E were found to have a 31 per cent reduction in risk of type 2 diabetes compared to those with the lowest intakes of this nutrient. Another nutrient that seemed to be associated with a reduced risk of type 2 diabetes was something known as beta-cryptoxanthin. High levels of this nutrient were associated with a risk reduction of about 40 per cent. This study suggests that eating foods rich in vitamin E (such as sunflower seeds) and beta-cryptoxanthin (such as peaches and papaya) may help to prevent diabetes.

Dear John

I have a six-year-old son who is healthy and eats well. However, in the past three weeks he has had two bouts of impetigo. He first suffered from this about a year ago. Any suggestions regarding what might help?
Kathryn Taylor, by email

Impetigo is a contagious skin infection, usually the bacterium staphylococcus aureus. It usually starts as fluid-filled blisters around the nose and/or mouth, which may burst and dry out to leave honey-coloured crusts. While your son eats a healthy diet, it’s likely that some supplementation may enhance the ability of his immune system to combat such infectious diseases. Each day, give him 250mg of vitamin C along with a multivitamin and mineral designed for children. If he won’t take them whole, add ground-up tablets or the contents of the capsules into a drink. Should he start to develop signs of another infection, increase the dose of vitamin C to 500mg per day for two weeks. You can also treat the skin with tea tree oil, which has been shown to kill staphylococcus. Put 10 drops of the oil in a cup of water and apply to the lesions with cotton wool twice a day.

· If you have any issues you would like Dr Briffa to address in his column, please email him on [email protected]. Please note that Dr Briffa cannot enter into any correspondence. You can also visit www.drbriffa.com. Before following any recommendations in this column, you should consult your own medical adviser about any medical problems or special health conditions.

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