Contrary to popular belief, running a marathon does not increase the risk of a heart attack. Health experts recommend nevertheless a medical checkup before embarking on such a race.
The image of the marathon runner who collapses, suddenly struck by a heart attack, just before or shortly after crossing the finishing line, is a troubling image that implants a seed of doubt in our minds. These tragic accidents, sometimes relayed by television cameras, are confusing. Sports, and in particular running, are, after all, supposed to improve our fitness and lower our risk of succumbing to a heart attack.
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A study published in the New England Journal of Medicine (NEJM) deals with this apparent paradox. Apparent because the authors of this study concluded that running a marathon (42, 195 kilometres) or a half-marathon “does not lead to an increased risk of heart attack”. According to them, this risk is, on the contrary, “low and even lower than that incurred by taking part in a triathlon or a jog”.
Mortality rate of 1 in 259,000
Dr. Aaron Baggish, of Massachusetts General Hospital, and his colleagues analysed such cases of heart attack among 10.9 million marathon runners and semi-marathoners between 2000 and 2010. Over the entire period, only 59 of these athletes suffered a cardiac arrest during and one hour after the race. Of those who suffered an attack, 42 have died resulting in a mortality rate of 1 in 259,000. This rate is 1 in 52,630 among those who take part in triathlons. The difference between the number of attacks and the number of deaths is due to the presence of medical personnel who could intervene quickly. So it is more likely to survive a heart attack during a marathon than if someone is at home.
A detailed study of these accidents and those deaths show that the majority of the victims suffered from cardiac deficiencies. In particular, the deaths were caused by hypertrophic cardiomyopathy, a condition characterised by a loss of elasticity of the heart muscle, making the heart less able to pump blood to the body. Since the age of the marathon runners have been increasing, many also suffered from atherosclerosis (deposit of plaques that reduce the blood flow to the heart). However, these problems can worsen when the person makes a violent effort, as during a marathon.
In addition to indispensable pre-deployment training, Dr. Aaron Baggish considers it essential that all candidates for this type of event first undergo a medical examination to detect possible heart failure. The risk of an individual depends on multiple factors such as high blood pressure and cholesterol, habit of smoking or family history of heart disease. In addition, it is important to ask the doctor about the risks and ways to minimise them.
Doctors’ recommendations include “no smoking one hour before and two hours after a sport” and “report to the doctor of any heart palpitation occurring during and just after exercise”. Such rules should however be obeyed by anyone who plans to do intensive aerobic exercise and is not reserved only for the marathon runners.
Frequently recommended in weight loss diets, dietary proteins have demonstrated their appetite-suppressing effects.
In Lyon a team of researchers working under Gilles Mithieux, the Director of l’Unité Inserm 855 ‘Nutrition and the Brain’, helped to explain the biological mechanisms responsible for this special property of protein that controls hunger. The researchers described in detail the chain reactions caused by the digestion of proteins that can deliver to the brain a message of satiety, even quite a long while after the meal. These results, published in the scientific journal Cell, might make it possible to plan a better management of obese or overweight patients and to create for them the best diet plan.
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The research team of Inserm, CNRS and Université Claude Bernard at Lyon has managed to explain in detail the feeling of satiety experienced several hours after a high protein meal. Their research helps to explain the exchanges between the digestive system and the brain, initiated by food proteins that are mainly found in meat, fish, eggs or certain cereal products.
In earlier studies, researchers have shown that ingestion of dietary proteins triggers glucose synthesis in the intestine after the assimilation of meals (a feature called gluconeogenesis). The glucose that is released into the blood circulation (portal vein) is detected by the nervous system which sends an ‘appetite suppressant’ signal to the brain. Better known for its action in the liver and kidneys to feed other organs with sugar, gluconeogenesis delivers an ‘appetite suppressant’ message to the intestine between meals, which affects us with the feeling we know as “satiety”.
With the help of this new research the researchers can accurately describe how protein digestion causes a double loop of chain reactions involving the peripheral ventral (via the vagus nerve) and the dorsal (via the spinal cord) nervous systems. A detailed exploration of the biological mechanism identified specific receptors (μ-opioid receptors) present in the nervous system of the portal vein, at the end of the intestine. These receptors are inhibited by the presence of oligopeptides, products of the digestion of proteins.
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Initially, oligopeptides act on the μ-opioid receptors that send a message through the vagus nerve and the spinal pathway to those areas of the brain that have a specialized role of decoding such messages. The brain then sends a return message that triggers gluconeogenesis in the intestine. The latter then initiates sending the “appetite suppressant” message to those areas of the brain that control food intake, such as the hypothalamus.
The identification of these receptors and their role in the intestinal gluconeogenesis will allow the scientists to consider new therapeutic leads in the treatment of obesity. The challenge now is to determine how to act on the μ-opioid receptors and sustainably regulate satiety. According to Gilles Mithieux, the leader of the research team, ‘Solicited too strongly, these receptors can become unresponsive. We should, therefore, find the best way to inhibit them moderately in order to keep their long-term beneficial effect in controlling food intake.’