2 THINGS YOU DIDN’T KNOW ABOUT ALCOHOL

Why do we need to constantly go to the loo when we drink? Does alcohol make us feel warm? Read on and find out…

Nearly most of us will have tried some kind of alcoholic drink in our lives and a large proportion will also consume alcohol on a regular basis. Some prefer to drink in moderation while others drink in excess. But most people lack the knowledge behind what happens when alcohol gets into their bodies.

The most amazing fact about alcohol that everyone finds surprising, is that consuming this drug actually causes body temperature to fall. This is contrary to what most people think: that alcohol actually raises your temperature. It is true that drinking a lot of alcohol will make people feel warm. However, what you feel is quite different to what happens to your body. Alcohol increases blood flow to the surface of the skin, a process known as vasodilation. Blood carries heat around your body, so increasing the surface area of the blood vessels to the outside, causes you to radiate and lose more heat. When you are in a warm climate, the body will cause vasodilation to promote heat loss. Meanwhile when it’s cold, the capillaries near the surface of the skin have a reduced blood flow, so less heat is radiated into the environment. When people drink alcohol in cold weather, they will start losing heat very quickly to the environment due to the increased blood flow to the surface of the skin caused by the alcohol. The vasodilation can be seen in pale skinned people as their face will turn red coloured.

Figure 1. The vasodilation caused by alcohol can be seen clearly in pale skinned people, as their faces blush. From http://genetics.thetech.org/online-exhibits/blushing-alcohol

People feel warm when drinking because they have a much larger supply of blood to the surface of the skin which carries heat. But in very cold weather, the heat is lost to the environment in a short matter of time, making core body temperature drop dangerously, which can lead to hypothermia and even death.

A thing which most people know is that when they binge drink, they have too many trips to the loo. But they probably have no idea why this happens and probably think it has to do with drinking large volumes of liquids. Alcohol blocks (inhibits) the production of antidiuretic hormone (ADH). This hormone is secreted from a region in the brain called the pituitary gland in order to maintain water balance (homeostasis). When the body needs water, ADH is secreted and causes the kidneys to reabsorb more water back into the body, so less is lost in the urine. When we drink too many fluids, less ADH is produced so more water passes into the urine. But alcohol inhibits the production of ADH, so most of the water you are drinking just goes into the urine. Drinking heavily will prevent sufficient water reabsorption, leading to dehydration which is one of the main causes of a hangover.

Figure 2. This diagram depicts the body response when someone is dehydrated in 2 different situations: under the influence of alcohol (left side) and under normal conditions (right side). When the person is normal and they are a bit dehydrated, the brain secretes ADH, which travels in the blood until it reaches the kidneys. This causes the kidneys to reabsorb more water back into the body, so less water is lost in the urine. Meanwhile, when someone has too much alcohol, they will be unable to produce much ADH, even though they need the hormone. This means that most of the water they are drinking ends up in the urine. The dehydration caused by heavy drinking can cause a hangover the next morning.

References

Blair-West, J.R., Brook, A.H., Gibson, A., Morris, M. & Pullan, P.T. (1979). Renin, antidiuretic hormone and the kidney in water restriction and rehydration. The Journal of Physiology, 294, 181–193.

Malpas, S.C., Robinson, B.J. & Maling, T.J. (1990). Mechanism of ethanol-induced vasodilation. Journal of Applied Physiology, 68(2), 731–4.

Wang, X.M., Lemos, J.R., Dayanithi, G., Nordmann, J.J. & Treistman, S.M. (1991). Ethanol reduces vasopressin release by inhibiting calcium currents in nerve terminals. Brain research, 551(1–2), 338–41.