What’s your poison?
Drinking Alcohol, often to dangerous excess, is an accepted part of many people’s lives. The pressure on those that do not drink, particularly the young, to “join in with the crowd” is immense. Recent research shows that drinking by 12-20 year olds (particularly girls) is increasing, despite the efforts that are now being made to emphasise the hazards that young drinkers face: significantly higher chances of developing clinical depression, greater chance of causing permanent physical damage to their internal organs and increased likelihood of unwise, unprotected sexual activity (with the obvious consequences).
The World Health Organisation (WHO) considers that alcohol is a significant threat to World health, causing as much death and disability as measles and malaria. In 1990, alcohol was responsible for ¾ million deaths (80% of them in rich countries like the UK), more than either tobacco or illegal drugs. In spite of this, many governments, whilst claiming publicly that they are concerned about the abuse of alcohol, seem unwilling to limit either production or consumption; possibly because worldwide, on average, governments earn nearly a quarter of their tax revenue from the drinks industry.
To understand why something that causes so much harm is such an important part of the world economy and own our social lives, we need to take a long, hard, look at both ourselves and our close animal relatives. When it comes to boozing, it appears we are not alone.
In the beginning, there was a bug…
What most people call alcohol is actually ethanol (C2H50H), one of the alcohol “family” of organic (carbon containing) chemicals. It is made by certain micro-organisms, principally yeasts, as they break down sugars to provide the energy they need to live (fermentation).
It’s most likely that humans first started deliberately seeking to control this process for their own purposes as far back as 10,000 years ago. Fruit, left in water to ferment provided a snack that didn’t go bad so quickly and a nice drink.
This may have been the origins of the brewing industry, but getting drunk started long before.
Blame it on the fruit.
Ripe fruit is packed full of sugars, ideal food for ethanol producing micro-organisms. Their spores, always present in the air, settle and germinate on the skin of the fruit. Thanks to the plentiful supply of food, they thrive, reproducing and spreading.
Ripe fruit is also the food of choice for many animals: monkeys, apes, fruit-bats, birds and butterflies (to name a few). The challenge for any fruit hunter - particularly one that lives in a tropical forest where fruits ripen throughout the year - is to find the tastiest, ripest, fruit, with the minimum of effort. This could well explain how animals of all shapes and sizes, including our own fruit-eating ancestors first acquired a taste for ethanol.
The theory goes something like this… A tree bearing a quantity of perfectly ripe fruit, will, thanks to colonizing micro-organisms, also produce ethanol. Because ethanol is highly volatile, it turns to vapour and spreads through the air easily. Any animal that can detect ethanol vapour and track down its source is going to be able to find trees with ripe fruit faster than its competitors, giving it a distinct advantage in the battle for survival. To our noses, ethanol has a distinctive smell that is instantly recognizable. Perhaps this is no accident but is in fact because our noses are adapted for sniffing it out, a relic of our evolutionary past.
Any animal that seeks out and consumes fruit that has a high ethanol content gets a double treat. Not only is such fruit rich in sugar, but ethanol itself, when broken down by the liver, is a rich source of energy that provides 29Kj/g (carbohydrate provides 16Kj/g, protein 17Kj/g and Fat 37Kj/g), but there is a risk. Any animal that consumes too much ethanol risks becoming intoxicated (drunk) and poisoned. So, where are all the drunk monkeys?
Actually, there are quite a few examples of drunken animals that have been described, and I’ve even lived with one.
Drunk as a parrot.
Elton the parrot was (and still is) a Citron-crested cockatoo, hatched in Wales at the zoo where I used to work. She used to travel everywhere on my shoulder. One day, when I was drinking a glass of wine with some friends, she surprised me by forcing her head between me and the glass so she could get at the wine. I’d never seen this behaviour when I was drinking tea and, intrigued, I let her take a sip. She didn’t seem keen on the taste, so I assumed that she’d leave wine alone in the future. However, whilst I was busy serving dinner, I saw, out of the corner of my eye, Elton, head in my wine glass, guzzling as much as she could. Soon after, she started staggering around, became aggressive towards one of my friends, flew into the wall and had to be put in a cage (for the safety of all). Next morning she was, “sick as a parrot”. Interestingly, this unpleasant end to her evening didn’t prevent her from trying to get her beak into wine glasses from then on, and she had to be restrained whenever a cork was pulled.
The discovery that Elton seemed drawn to wine, even before she knew what it was, got drunk as a result of consuming too much, and suffered afterwards with a hangover – all, weaknesses I’d considered uniquely human up to then – started me looking for other examples of alcoholic animals. I didn’t have to look far.
In Sri Lanka, a popular local drink, Toddy, is made from the nectar of coconut flowers. Holes are made in the base of the flowers and cups tied underneath to catch the nectar that drips out. These are then left in the trees whilst the wild yeasts and fungi do their work. Monkeys that raid the pots and drink the fermenting Toddy often cause problems for local villagers.
Worker wasps and hornets, deprived of their normal food at the end of summer, take advantage of over-ripe summer fruits, the erratic flight that results, with multiple collisions, is often put down to “sleepiness”. Rubbish, they’re drunk. Fruit eating birds like waxwings are similarly famous for falling off their perches and flying into walls. Nectar drinkers, like the lorikeets of Australia are also guilty of flying whilst “over the limit”.
If the thought of a drunk parrot doesn’t frighten you, how about a drunk elephant? After pigging out on their favourite fruit (from the Marula tree) followed by a big drink of water, their stomachs become giant fermenting vats. As a result, the elephants become uncoordinated, aggressive and incredibly dangerous. Presumably, the headache next morning must be pretty big as well.
The list goes on, clearly supporting the “nose for booze” theory. One thing is still puzzling however: if drunkenness is an unpleasant side effect of eating alcoholic fruit, and animals are very good at detecting ethanol, why don’t they avoid the fruit that would make them drunk, or at least be cautious about eating too much? Observations would seem to suggest that they seem especially drawn to the booze.
Ethanol is fascinating because it is an incredibly simple molecule and yet its effects on animals’ brains and bodies are far-reaching and profound. Despite the terrible damage it does, animals continue to seek it out. To understand why, perhaps we should look at what it does.
Ethanol is quickly absorbed into the blood stream as it does not need to be digested. This begins in the stomach but principally takes place in the small intestine. This is why alcohol that arrives in the stomach mixed with food takes longer to be absorbed. Once absorbed, it travels throughout an animal’s body. Thanks to its chemical structure, it can dissolve in both water and fat. In a short time it is distributed evenly in every tissue. Because it is the level of alcohol actually circulating in the blood which determines how drunk an animal becomes small animals become intoxicated faster.
Not all ethanol that enters an animal’s bloodstream has an effect, some leaves straight away without being broken down. Between two and ten percent is removed by the kidneys and lungs. The exhaled ethanol vapour allows the police to catch drunk drivers. An ethanol content of 35mg per 100ml of exhaled air is equivalent to the current UK drink-driving limit of 80mg per 100ml of blood.
The job of breaking down ethanol falls to the liver, which has to go into overdrive to cope with the extra work. It’s a two part process that first sees the alcohol turned into acetaldehyde by the enzyme Alcohol dehydrogenase. This intermediate is toxic and thankfully, is normally converted by aldehyde dehydrogenase into acetic acid (vinegar). The acid is then further broken down into water and Carbon Dioxide elsewhere in the body. Whilst the liver is busy with alcohol breakdown, many of it’s other, essential functions are affected. This can be especially dangerous for young drinkers.
Interestingly, after consuming ethanol, animals become hungry. This is due to the breakdown of the glycogen-glucose shunt, a system that normally ensures that there is enough, but not two much glucose in the blood. A healthy human has blood that contains 50-80mg of glucose per 100ml of blood. The liver maintains this safe level. If the blood sugar rises too high, the liver converts the excess glucose into glycogen. When the glucose level starts to drop, the liver reverses the process. This allows you to eat irregularly yet function constantly. Alcohol blocks the system forcing the blood glucose levels to drop, setting off alarm bells in the brain, which instantly sends out chemical signals to stimulate appetite. The practise of having an aperitif, a moderately strong alcoholic drink before a meal to make all the diners feel hungry, takes advantage of this effect. It is also the reason why kebab shops do so much business after the pubs have closed.
Another general effect of ethanol that seems to confuse many people, and one of the main causes of hangovers, is dehydration. You would think that if you were drinking something like lager, which is in the region of 90-95% water, you couldn’t possibly dehydrate. Once again, the ethanol is playing tricks with the body, or, more accurately, the section of the brain that monitors the level of water in the blood. It blocks the production of vasopressin (anti-diuretic hormone), something that would only normally occur if there was too much water in your blood. This sets the kidneys into “dump water” mode and results in the loss of much needed body fluid. Along with all the extra fluid, the kidneys manage to lose essential mineral salts that are needed by your metabolism: magnesium, potassium, calcium and zinc. The blinding headaches that traditionally follow an excess of alcohol are often little more than brain shrinkage as a result of this dehydration combined with salt loss.
So far, nothing in this list of effects explains why any creature would want to consume ethanol. To understand that, we have to look in a little more detail into the effects of ethanol on the brain.
It’s all in the mind
Unlike most drugs that affect mood, ethanol doesn’t have a single “target” location in the brain. It affects a number of different sections of the brain and has varying effects based on the concentration present in the animal’s blood.
At relatively low levels ethanol makes the thinking, remembering and pleasure seeking parts of the brain (the cortex, hypocampus and nucleus accumbens) more sensitive to stimulation. Signals are transported more easily and the motor and reward (pleasure) centres fire more readily. In humans, these effects are usually observable after a single drink, whilst the levels of ethanol in the blood are relatively low (25mg/100ml). A person who has this much ethanol will typically be more sociable, more willing to tell jokes, smile and laugh. They may feel less intimidated by strangers and more confident in themselves. They will also be more physically animated. At this level of intoxication there are few unpleasant side effects to speak of. Sadly, the feelings of empowerment that accompany the first drink invariably lead to a second.
As the levels of ethanol increase (50-80mg/100ml in humans) the above effects become more pronounced. The animal becomes more excitable. At this stage of drunkenness, people at a party would start talking louder and faster than ever as their inhibitions melted away.
The feelings of happiness increase along with the ethanol levels in the blood for a little while longer before something interesting happens. The receptors that have been over-stimulated up to now suddenly stop responding. The ethanol now begins to act as a sedative, selectively reducing brain activity. The first section of the brain to slow down is the hippocampus, which affects memory, and the thalamus, which controls sensory and motor information. In humans this corresponds to a blood alcohol level of around 100mg/ml (3-4 drinks). By now, our partygoers would be getting clumsy on the dance floor, swaying slightly as they tried to stand upright and losing the thread of conversations.
Now that the switch from stimulation to sedation has occurred, further increases in the blood ethanol level just do more and more damage. When a person hits an ethanol level of around 120mg/ml there are whole sections of their brains shutting down. Activity in the areas of the brain involved with motor coordination and posture (cerebellum) is reduced causing slurred speech and an increased likelihood of falling over. The sight centre (occipitial lobe) is also affected, causing blurred vision.
Animals at and above this level of intoxication can become unpredictable as their seratonin receptors now start to be affected. Seratonin is an important brain messenger and it is known to control overall mood, aggression and sexual arousal. A human will, at this point either start a fight, start trying really hard to impress members of the opposite sex or go to sleep. Exactly which of the three possibilities is most likely depends on the personality of the individual and the exact circumstances.
At around 200mg ethanol per 100ml of blood a human is usually in real trouble. If they haven’t dropped off to sleep by now, they will probably be feeling very ill and confused. Their vision will be blurred, their hearing will be dulled, speaking and understanding speech will have become difficult, as will standing unsupported. Plus, thanks to the alcohol that has diffused into the fluid-filled balance centres of the inner ear, the room will be spinning alarmingly.
If ethanol levels rise any further, the animal will be in real trouble as essential sections of the brain start to shut down. For humans, 500mg of alcohol per 100ml of blood is usually fatal. Breathing stops.
|This article first appeared in Scitec magazine (2003).|