A study of mice in Texas and human beings in Europe revealed why alcohol and sugar make us thirsty. The findings of the study were published in the journal Cell Metabolism on April 12.

Researchers from the University of Texas (UT Southwestern) found the hormone FGF21 played the role of an anti-dehydration mechanism by acting on the brain to increase the desire to drink water. This was said to happen in response to specific nutrient stresses that lead to dehydration.

"We knew that exposure to alcohol or sugar turns on production of FGF21 in the liver. What we now show is that this hormone then travels in the blood to a specific part of the brain, the hypothalamus, to stimulate thirst, thereby preventing dehydration," said Dr. Steven Kliewer, Professor of Molecular Biology and Pharmacology at UT Southwestern Medical Center. "Unexpectedly, FGF21 works through a new pathway that is independent of the classical renin-angiotensin-aldosterone thirst pathway in the kidneys."

The FGF21 hormone is primarily secreted by the liver. This week, another report found a particular variation of the gene was not only responsible for inducing sugar cravings but was also linked to lower body fat.

In the mouse study, researchers conducted an experiment with regular mice and rodents that were genetically unable to produce FGF21. When they were given ketogenic diet (high in fat and low in carbohydrates), the hormone could stimulate water-drinking in regular mice. But the rodents genetically unable to produce FGF21 failed to increase water intake in response to the nutritional stress.

Meanwhile, 21 people from the Medical University of Graz in Austria were recruited for the human study. The participants were randomly assigned to drink only juice or a mixture of alcohol and juice. Over a period of four hours, researchers measured the levels of FGF21 in their blood. The participants who consumed the alcohol-juice mixture saw their FGF21 levels peak at around two hours and decline afterward.

"This suggests that FGF21 might someday be used as a drug to limit alcohol consumption and protect against its effects in people," said Dr. David Mangelsdorf, Chair of Pharmacology, Professor of Pharmacology and Biochemistry at UT Southwestern Medical Center. He added that the hormone appears to be regulated similarly in both human beings and mice.

To stimulate thirst, FGF21 traveled in the blood to a region of the brain known as the hypothalamus. Thirst induced by the hormone seemed to depend on a signaling pathway known as the β-adrenergic circuit, the researchers stated. They added this study may introduce a new perspective to metabolic research, which has generally examined feeding behavior as opposed to hydration.

"To put this in context, we always look at food intake, and the metabolic field has spent comparatively little time studying water intake," Dr. Kliewer stated. "This study suggests that we should think more about hydration and how it might contribute to metabolism."