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Energy for the heart

An increase in blood sugar can help in recovery after a heart attack

SCIENCE PHOTO LIBRARYOne of the possible consequences of a heart attack is a temporary resistance to insulin, a condition leading to higher concentrations of sugar (glucose) in the bloodstream. Doctors usually take a negative view of this metabolic outcome, as it is normally associated with a greater risk of diabetes and rate of mortality. However, a new study points to a possible solution where before only a problem was seen.  The most recent findings of a group of researchers led by Dr. Andrei Sposito, a cardiologist and professor at the University of Campinas (Unicamp), show that insulin resistance is essential for supplying more energy to the heart, thereby contributing to the organ’s recovery.

The Unicamp researchers collected blood samples from approximately 500 patients at the Hospital de Base in Brasília in two phases: during the first 24 hours after a heart attack and, again, five days later. Patients whose insulin resistance increased before declining gradually and moderately after five days showed better clinical results and faster recovery, but according to data presented in an unpublished article constituting the doctoral thesis of Dr. Felipe Azevedo Moura, of Sposito’s research group, defended in May 2016, this change did not occur in all patients.  In some patients, insulin resistance would increase and decline rapidly; or increase very little, level off and remain so for a number of days. Such cases were considered extreme, presenting a worsening of the patient’s clinical status and an increased risk of death. “The data show no linear correlation between mortality and increased insulin resistance,” says Sposito. The greatest risk of cardiovascular complications was found to be distributed equally at the two extremes of a U-shaped graph (see above), which shows either a very extreme or very small decrease in insulin resistance over the first days following a heart attack.

Sposito suggests that such alterations in insulin resistance might be the body’s way of providing the heart sufficient energy for it to recover. Heart attacks are caused by fatty deposits of plaques that obstruct the flow of blood to the heart.  With blood flow reduced, the heart is deprived of sufficient oxygen to produce essential fatty acids—the ideal fuel that keeps the organ pumping. Glucose then acts as a way out. “This mechanism seems to be a function of our metabolism,” Sposito explains. “There is a biological imperative to protect the heart by supplying more glucose and controlling its availability through insulin resistance.” According to Sposito, research opens the way to new possibilities whose mechanisms must be revealed through further study.

Dr. Maria Lúcia Corrêia Giannella, an endocrinologist and University of São Paulo School of Medicine (FM-USP) professor who did not participate in the study, sees the beneficial effect of insulin resistance as a plausible hypothesis, but suspects that it might be a coincident phenomenon lacking any cause-and-effect relationship. “Insulin resistance occurs in situations of intense stress, such as heart attacks or acute infections,” Giannella explains. At these moments, “stress hormones” (such as glucagon and cortisol) are released that counteract the effects of insulin.

Late diagnosis
The direct relationship between the diabetes and the risk of cardiovascular problems had already been demonstrated in numerous studies, including that of the Unicamp research group. In a 2013 article published in the journal Current Medical Research and Opinion, Sposito, along with colleagues from his institute and the University of Brasília (UnB), points out that that the death rate following a heart attack is twice as high among diabetics as compared to non-diabetics. For undiagnosed, untreated diabetics, the risk of death can be four times greater. “Even treatment with the most basic medication, such as that provided the Unified Health System (SUS), reduces the risk of death by half,” says Sposito.

Giannella points out that type-2 diabetes, which accounts for about 90% of all cases of the disease, begins very subtly and asymptomatically, often delaying a diagnosis by several years. A 2014 study by the International Diabetes Federation estimates 3.2 million undiagnosed diabetics in Brazil alone. “It’s important to be attentive to the risk factors for diabetes so that a diagnosis can be made and proper treatment can be administered,” explains Giannella. “A lot of people find out that they have the disease only when receiving medical treatment for an acute heart attack, when complications can be fatal,” she warns.

Scientific article
FIGUEIREDO, V. N. et al. Diabetes mellitus unawareness is a strong determinant of mortality in patients manifesting myocardial infarction. Current Medical Research and Opinion. V. 29, pp. 1423-27. 2013.