Mar 132016
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A recent study performed by a French team examined the long-term effects of sugar intake in rats [1]. The purpose of this experiment was to investigate whether its excessive consumption during adolescence alters the brain reward system.

It is known that, during the development of the mammalian brain, there are specific time windows in which its proper functions are established [2]. These time windows exceed the prenatal development and last until early adolescence. In particular, the brain reward system could be sensitive during adolescence. If it is over- or in-active in this period, it is possible that this causes disorders such as addictions or depression [3].

The French researchers exposed adolescent male rats to sucrose solutions. The rats were free to choose between them and a supplemental bottle containing water. Similar to some of us humans, the sugar-exposed teen rats developed a sweet tooth and consumed more sugar solution than water. The sucrose bottle was removed from their home cages after 16 days. Later, when they were adult animals, their reactions toward sugar intake and their reward circuitry were examined. The rats behaviorally responded less toward sugar consumption than animals of a control group, which did not consume sugar in their adolescence. To put it into more anthropomorphic terms, they were not as excited about the reapplication of sugar. In addition, the researchers found that a key area of the brain reward pathway, the Nucleus accumbens, was not as active as in the control group. These results suggest that an overconsumption of sugar during adolescence alters the development of the brain reward circuitry. Consequently, sweet water does not seem appealing anymore in adulthood.

So, what could these findings mean for humans? Should we give more sweets to teenagers and hope that they lose interest in them later? Does that work with all “bad” substances, for example alcohol and other drugs? For sure, the answer to all of these questions is: “No!”. Firstly, the study showed that excessive sugar consumption led to a deficit in the reward system. These deficits could manifest themselves in other, more severe behavioral deficiencies. To name some of them, psychiatric disorders that have been linked to a dysfunctional reward system include depression, schizophrenia and substance abuse. Secondly, other studies have shown that adolescent alcohol consumption in rats causes severe damage to the brain, reaching from altered network function to cell death [4]. However, this study does neither fully explain whether excessive sugar intake during adolescence causes severe reward-related disorders, nor whether the findings apply to humans as well. What these experiments do tell us is that teenagers and adults should only moderately consume sweets, not only because they are unhealthy, but also in order to foster our mental health.

-Theresa Weidner

[1] F. Naneix, F. Darlot, E. Coutureau, M. Cador, EJN 2016, 46, 671-680.
[2] C. Rovee-Collier, Dev. Psychol. 1995, 31(2), 147-169.
[3] T. Paus, M. Keshavan, J. N. Giedd, Nat. Rev. Neurosci. 2008, 9, 947-957.
[4] C. Guerri, M. Pascual, Alcohol 2010, 44(1), 15-26.

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