Thirst Lecture 56 PDF

7/13/22 Thirst Based upon Logue Ch.3 Appetite: The psychology of eating and drinking 1 1 Introduction - Water • 97% of Earth’s water is in the sea, with only 3% being fresh and thus potentially suitable for drinking, food production (notably animal production), energy and industrial uses • Fresh...

7/13/22 Thirst Based upon Logue Ch.3 Appetite: The psychology of eating and drinking 1 1 Introduction - Water • 97% of Earth’s water is in the sea, with only 3% being fresh and thus potentially suitable for drinking, food production (notably animal production), energy and industrial uses • Fresh water resources that are accessible (notably ‘fossil water’, lakes and rivers) represent only about 0.7% of all of the water on Earth • It takes around 3000 litres (12 bath tubs) of water to generate the food that the average Westerner consumes in one day, with 400 litres (1.6 bath tubs) per person per day for household uses – a level completely unsustainable if everyone were to adopt our current eating and water usage habits 2 2 1 7/13/22 Water… • Perhaps not surprisingly, fresh water is becoming an increasingly scarce resource and several leading political figures have warned that it (along with food) has, and will increasingly provide, the basis for armed conflict – One significant ‘water flash-point’ is in the Middle East • • Egypt has threatened military action if the upper reaches of the Nile are ever dammed (as they currently are being by Ethiopia’s ‘Grand Renaissance Dam’ on the headwaters of the Blue Nile) Israel’s 1967 bombing of Syria when it attempted to divert the headwaters of the Jordan river • Not only is access to fresh water a problem at the National level, it also a local problem too – Many people do not have easy access to fresh water • Out of the worlds population of 7 billion people, 3.5 billion have access to piped water (private), 2.1 billion rely on standpipes (public sources), and 1.4 billion are completely unsupplied – Many people do not have access to safe drinking water • As of 2017, 0.8 billion people lacked access to safe drinking water, and waterborne diseases (mainly from sewage contaminated water supplies) are estimated to have caused 0.5 million deaths in that year alone 3 3 Water… • As should now be apparent easy access to plentiful clean fresh water is something of a luxury • It is then hard for most of us to imagine what extreme thirst must be like • A good example, which captures something of this terrible experience, was provided by Sven Hedin, a 19th Century explorer • He was severely dehydrated after crossing the Taklamakan desert and he recorded his experience of finding water and of sating his thirst… 4 4 2 7/13/22 Thirst • • I stood on the brink of a little pool filled with fresh water. It would be vain for me to describe the feelings which overcame me. I took my tin box filled it and drank. How sweet that water tasted! Nobody can conceive it who has not been within an ace of dying of thirst. I lifted the tin to my lips and drank, drank, drank, time after time. How delicious! What exquisite pleasure! The noblest wine pressed out of the grape, the divinest nectar ever made, was never half so sweet. I do not think I exaggerate, if I say that during the first 10 minutes I drank between five and six pints. At that moment it never entered my head that, after such a long fast, it might be dangerous to drink in such quantity. But I experienced not the slightest ill effect. On the contrary I felt it infusing new energy into me. My pulse, which had been so feeble, now beat strong again. My hands, which had lately been dry, parched and hard as wood, swelled out again. My skin which had been like parchment, turned moist and elastic. And soon afterwards an active perspiration broke upon my brow. In a word, I felt my whole body was imbibing fresh life and fresh strength. It was a solemn, an awe inspiring moment. 5 5 Extremes • Whilst one can last an extended period of time without food, dehydration rapidly kills – The speed of death is heavily dependent upon climatic conditions, but most people die when their water deficit is between 15-25% of bodyweight (c12 litre loss) – Strong thirst ensues at around a 2% deficit – A fit adult can still function at 3-4% deficit – At 5-8% severe fatigue and apathy ensue – At 10%+ gross physical and mental deterioration are evident. Delirium may ensue, followed by coma and death • Dehydration is problem in children and a serious (sometimes fatal) problem in the elderly – Both may have insensitive interoception (i.e., don’t feel thirst) – In elderly, blunted receptor sensitivity 6 6 3 7/13/22 So what is thirst? • We can define two kinds of thirst and hence of motivations to drink – The first is homeostatic drinking (the kind we have been thinking of so far). Here the body attempts to maintain a set point, with behaviour kicking in to regulate water consumption when deviations from the set point occur – The second is non-homeostatic drinking, such as anticipating future water needs • We will now look at some examples of both 7 7 Homeostatic drinking • There are two main types – Eating • If a person is water deprived they eat less. Similarly if they are food deprived they drink less • A ratio of 1 part water to 1 part food (stomach) and 3 parts of water to 1 part food (intestine) are needed for digestive purposes • This represents a type of set point that the body uses to maintain adequate levels of hydration 8 8 4 7/13/22 Homeostatic drinking • Blood, plasma and cells – Fluid in the body can be categorised into two compartments • Fluid inside cells • Fluid outside cells (blood & plasma) – Loss of fluid from within cells can cause thirst (e.g., increased salt in blood plasma, draws water out of the cell and produces thirst) – Loss of fluid from outside cells can also cause thirst (e.g., blood loss) • Both represent further and separate set points 9 9 Non-homeostatic drinking • Time – Some animals prefer to drink mainly at night even if they eat in the day Rats Day Night Food consumption 50% 50% Water consumption 25% 75% • Anticipatory drinking – Most of us drink whilst we eat – But the need for water caused by food can not produce an immediate need for water, hence the name anticipatory drinking – Animals show this too in topping up whilst water is available (drink while you can) 10 10 5 7/13/22 Non-homeostatic drinking • Schedule induced polydipsia* (SIP) – If a rat is given a food pellet at the rate of 1/min for 3 hours, the animal will consume up to 50% of its bodyweight in water if it is given free access to water during this time – SIP can also be observed in humans playing on slot machines and experimentally too • Polydipsia in psychiatric patients – 6-17% of chronic psychiatric patients are polydipsic – Of these, 70% have schizophrenia • Some of this is delusion related (e.g., inner cleansing) – Such patients may drink 20 litres/day – It is hard to control and can be fatal *Means ‘lots of drinking’ 11 11 Explaining thirst • So then, what mechanisms underpin homeostatic and non-homeostatic drinking? • We will now look at three types of explanation – Peripheral mechanisms (outside the CNS) – Central mechanisms (CNS) – Combined mechanisms • Even though thirst only involves one type of stimulus - water - it turns out to be rather complicated and as we shall see the body utilises several mechanisms in parallel 12 12 6 7/13/22 Dry mouth theory • The dry mouth theory was first proposed by Walter Cannon. It is an expressly peripheral model • When we are thirsty our mouth becomes dry, and, ergo, a dry mouth causes thirst • Evidence? 13 13 Evidence for dry mouth theory • Saliva levels in the mouth strongly correlate with levels of water deficit • Anaesthetising the mouth of thirsty dogs (and humans) alleviates thirst • If water is placed directly into a thirsty animal’s stomach, the animal will still drink a roughly equivalent amount of water. The net amount drunk will exceed that drunk by an animal without water placed in the stomach – It is like the mouth has to feel the water and become less dry for thirst to be assuaged 14 14 7 7/13/22 Evidence for dry mouth theory • Thirsty camels will drink 30% of their bodyweight in water in 10 minutes • That is 200 litres of water at 20L/minute! • This is long before that water could have physiologically relieved their water deficit • In sum, a dry mouth (and lack of) appears a good index of when to start and stop drinking • But is it the cause of thirst? 15 15 Evidence against • In 1925 a man attempted suicide by cutting his own throat. He failed, but did manage to make a gaping hole in his oesophagus – When he drank, water just spilled out the hole – He became very very thirsty and so tried pouring water directly into his oesophagus (i.e., into his stomach by-passing his mouth) which relieved his thirst • Animals and humans who lack salivary glands (and have a chronic dry mouth) drink normally • It cannot account for non-homeostatic drinking • Subjective sensation of thirst and the insula cortex • This sensation is supported in part by the insula, but damage to the insula does not disrupt normal drinking • Dry mouth is a signal (i.e., correlate) of, not a cause of, thirst 16 16 8 7/13/22 Central mechanisms • • Is there a central brain area responsible for thirst? Such an area would have to meet at least two criteria for it to be a contender – It should collect information about water levels in the body – the information criterion – It should be able to start and stop drinking – the control criterion • The hypothalamus ([below left] and in particular the median preoptic nucleus [PO below right) located in this structure) has been suggested as one such possibility - does it meet our criteria? 17 17 Hypothalamus and thirst • Information criterion - (detect water deficit) – Specific cells in the hypothalamus are sensitive to variations in salt levels in blood plasma – The hypothalamus reacts to other peripheral signals too (e.g., vasodilation) – The hypothalamus receives inputs from other sensory receptors located outside of the blood brain barrier that monitor bodily systems • Control criterion - (correct water deficit) – Saline injected into the hypothalamus triggers drinking – Electrical stimulation of the hypothalamus does likewise – Lesions of the hypothalamus disrupt drinking • So how might it control drinking? 18 18 9 7/13/22 Hypothalamus and thirst • How does the hypothalamus control drinking? – The hypothalamus controls release of Antidiuretic Hormone (ADH) – ADH release, increases water retention by kidneys (conserving water) and raises BP – ADH is released when: – Loss of fluid from within cells (e.g., from increasing salt levels) – Loss of fluid from blood or plasma (e.g., from falling blood pressure) 19 19 Problems… • Nobody doubts that the hypothalamus is involved in producing thirst and drinking behaviour • But does it have the‘ultimate say’? • Probably not, because there are other peripheral systems that appear to work cooperatively, but independently, of the hypothalamus • The best studied relate to the Kidney 20 20 10 7/13/22 The kidney • Arterial blood pressure falls as water deprivation ensues and salt levels increase – The kidney detects these changes and releases a hormone called renin – Renin in the blood causes release of a further hormone, angiotensin – Angiotensin then affects the CNS (drinking) – In addition, angiotensin • Constricts blood vessels (raising blood pressure) • Increases release of ADH 21 21 Blood pressure and thirst • Note the close link between blood pressure and thirst – African-Americans have heightened rates of high blood pressure • It has been suggested they may be‘super-sensitive’ to angiotensin • This may have arisen from a selection pressure, in which only those individuals who could survive the dehydration on a slave ship (i.e. those most sensitive to angiotensin) lived to reproduce…. – 20 million people forcibly transported with a 15-30% death rate – Dietary salt and blood pressure • High levels of dietary sodium (i.e., salt) seems to increase blood pressure and hence risk for stroke as people age • This is why there is pressure in many countries to reduce the amount of salt we eat, especially hidden salt in processed foods (e.g., 6 slices of white bread = half your recommended daily intake) 22 22 11 7/13/22 Summary so far • Thirst then results from a complex interplay of peripheral and central mechanisms • These involve departures from set points at which different, but overlapping and interrelated systems kick in to get an animal (or us) to feel thirsty and drink • This still leaves us with a need to explain non-homeostatic drinking… 23 23 Explaining NHD • SIP (schedule induced polydipsia) – SIP appears maladaptive, but is not so in the environment – If an animal is very hungry, it might continue to search for food totally disregarding ALL other needs – Consequently, animals show a phenomenon called displacement, in which one activity can temporarily replace another – This allows a hungry animal to engage in other useful activities (such as drinking) which might not occur if the animal could not switch from one goal to another 24 24 12 7/13/22 Explaining NHD • Anticipatory drinking – This often occurs when we eat – It turns out that chemical changes that take place when we see/smell food and in the early stages of eating may trigger thirst • Histamine is released upon the sight of food and triggers drinking • Insulin release also triggers drinking and is released during food intake • Learning (e.g., desert nomads) 25 25 Conclusion • Thirst is far more complex than one might imagine and involves interplay between peripheral and central systems • But human drinking behaviour is more elaborate still, because it is the primary mode for consuming the worlds most popular drugs - caffeine and alcohol, the main focus of the next lecture. 26 26 13 7/13/22 For S2: A brief interlude on writing reports... • How do you write a good report? – The worst bit is usually the discussion…. – Must haves… » Interpret the findings relative to the aim » Briefly restate aim and indicate whether supported or not » Examine what the findings suggest » If confirmed, then this means… (& If not….) » Whether this fits more broadly with previous research » If yes, this means.. (& If not….) – Important, but more so in some cases than in others » Any meaningful limitation » By meaningful, I mean would an educated person likely think this to be the case (a big one being causation vs. correlation) » Any meaningful (as above) alternative explanation » Where might this line of research go next? 29 29 Drugs and food • Reading Logue Ch. 11 • Appetite: The psychology of eating and drinking The print on the right is called ‘Gin Lane’ and was drawn by Hogarth in 1751. It is an early example of health promotion, as the print depicts the multiple evils that arose from the very popular, very cheap and easily available gin. This print contrasted with another entitled ‘Beer street’, which depicts a far nicer place. Hogarth amongst many others were involved in lobbying for better price and quality controls on gin, as it was producing enormous social problems at that time. 30 30 15 7/13/22 Overview • In this lecture we will examine three things, all of which are intimately related to feeding and drinking in humans – Alcohol consumption – Caffeine consumption – Finally, we will briefly look at whether certain foods can be considered as ‘addictive’ 31 31 Alcohol • The word alcohol derives from the Arabic for ‘something subtle’ (a fitting description?) no • Evidence of brewing (‘beers’) dates to the Neolithic period (C8-10,000 years ago) and there appears no rationale for consumption other than its psychoactive effects • Distillation dates back to the Arabs, who appeared to invent it about 800AD, its use had spread throughout Europe by the middle ages • Before considering the effects of alcohol consumption, we need to consider the context in which drinking takes place - so what does drinking mean in the Australian context? 32 32 16 7/13/22 Drinking - The Australian context • Commenting upon Australian national identity a social historian said “To judge from contemporary accounts, no people on earth ever absorbed more alcohol per head of population than Australians” • The image of the heavy drinking Australian is part of the national myth • The myth starts with the first fleet, a rum issue on the day of the landing and the drunken behaviour that ensued • So is this‘national myth’ true? 33 33 Drinking - The Australian context • Drinking in the early days of the colony was pretty much identical to that in most other Anglo-Saxon countries at that time - around 13 litres of pure alcohol/per person/per year • Alcohol exerted its most devastating effect on Indigenous Australians – Liquor was used as payment for labour, sexual favours and for entertainment – It is ironic indeed that the stereotype of the ‘drunken aborigine’ is in marked contrast to the national myth 34 34 17 7/13/22 Drinking - The Australian context • • • • • During the 1800’s the pub started to become the focal point of alcohol consumption In Sydney, in 1837, there was 1 pub for every 100 Sydneysiders (even more if sly-grog shops were included too) During the 1900’s with urbanisation and industrialisation - and the consequent need for greater sobriety - alcohol consumption fell to a low of 2.5 L during the great depression (1929-1933) There were many social advocates for sobriety, who were colloquially termed ‘Wowsers’ – defined as “A very pious person who mistakes the world for a prison and themselves for a warder” Current consumption is around 9 L, with the NT topping the bill at 13 L and Victoria with the lowest – but with considerable variation – Highest in rural areas, especially in WA, and some remote indigenous communities 35 35 Drinking in Australia today • Today, around 90% of people aged 14 and up have drunk alcohol • Australia is ranked 23rd in the world, in terms of per capita consumption - pretty good (in health terms) but not from the perspective of national mythology • What has changed is what we drink – A shift from beer to wine – A shift to light beers – The advent of the pre-mixed drink or alcopop • The latter is especially challenging for public health, with marketing and ‘taste’ directed at novice drinkers par$cularly underaged drinkers – People can not tell apart (under blind tasting conditions) a vodka mudshake from chocolate milk – the sugar and cream completely mask the alcohol – These sort of drinks can form ‘entry points’ for teenage (especially female) alcohol consumption 36 36 18 7/13/22 Alcohol - impact • Positives – Tax revenues from Alcohol in Australia have averaged around 6 Billion Dollars per year over the last decade – Alcohol consumption reduces cardiovascular deaths by approximately 800 cases per year, and prevents around 20,000 hospitalisations – It also acts to reduce kidney/gall-bladder stones and increases bone density – Hotels can act as focal point for communities – Alcohol consumption can be a pleasurable experience 37 37 Alcohol - impact • Negatives A standard drink delivers 15mls of alcohol – 15% percent of men and women aged 20-29 drink at a rate likely to cause them harm (> 2 standard drinks/day). – Among this age group 50% of men and 20% of women have engaged in binge drinking (> 7/5 standard drinks drunk consecutively) at least once a week in the past year. – Harms from excessive intake include: • • • • • • • Cirrhosis (liver damage) Heart disease Brain damage Road trauma Violent behaviour Relationship breakdown Lost productivity – The rate of excessive consumption in Indigenous Australians is 2-3 times higher even though fewer drink 38 38 19 7/13/22 Alcohol - impact • Alcohol’s yearly adverse health impacts in Australia (averaged over the last decade) Condition Deaths Hospitalisations Cancers 1500 10,180 Cardiovascular diseases 1150 10,700 Digestive diseases 780 9,700 Injuries 1495 65,000 Neuropsychiatric 380 157,130 Total 5305 252,710 • Alcohol abuse/misuse costs around 15 Billion dollars per year in Australia (and rising) 39 39 Alcohol - impact • For all drug treatment services in Australia, alcohol related problems were the most common reason for referral • Approximately 35% of all violent offences are committed under the influence of alcohol • The yearly ABS victims of crime survey reveals around – 1.5 million people were verbally abused by someone under the influence of alcohol – 0.6 million had property damaged by someone under the influence of alcohol – 0.4 million were physically assaulted by someone under the influence of alcohol • These types of statistics (and much more) can be found for every nation that consumes alcohol 40 40 20 7/13/22 The effects of alcohol • Metabolism and male vs female differences – Alcohol enters the bloodstream and is rapidly absorbed by the brain, but much more slowly by muscle (women have less muscle) – Alcohol is primarily (90%) metabolised by the liver (and 10% by stomach - but women are less efficient at this) • Alcohol is broken down into Acetaldehyde (women less efficient at this as well) • Acetaldehyde is broken down into Acetate • Acetate is then fed into the ACoa pathway yielding 7Kcal for every gram of alcohol consumed • The body can metabolise a maximum of 6-8g per hour 41 41 Psychological effects • General - euphoria, disinhibition, reduced anxiety, impaired motor control • Specific - effects of alcohol need to be distinguished from peoples expectations of what happens on ingestion – Expectation free research designs tell us that • • • • Alcohol lengthens reaction time Alcohol narrows attention Alcohol promotes risk taking Alcohol enhances aggression – This makes for a very unfortunate cocktail when combined with a car and an inexperienced driver 42 42 21 7/13/22 Effect on the brain • Alcohol acts upon multiple brain systems, which is why it is called a promiscuous drug • Its effects also vary by dose • The key changes appear to be: – It acts akin to anaesthetics by increasing the permeability of nerve cell membranes (consumption of the anaesthetic agent ether is also intoxicating) • Alcohol can be used as an anaesthetic but its therapeutic dose is so close to its lethal dose it was never of much practical use – It acts upon the same GABA receptors as anti-anxiety drugs such as diazepam (which is 4000X more potent) – It alters brain dopamine levels, especially in the Nucleus Accumbens (driving wanting) – It increases levels of endogenous opioids (producing liking) 43 43 Tolerance • The behavioural and pharmacological effects of alcohol change with exposure - that is, tolerance • Acute tolerance – Within a drinking session rising blood alcohol (BA) correlates well with behaviour change. After drinking ends BA can still be elevated but there can be a disconnect between behaviour and BA: • One can feel sober even with both an elevated BA and significant impairment in things like reaction time, attention etc • The classic example is driving the morning after heavy drinking the night before – feeling sober, but impaired and with an elevated BA • Chronic tolerance - metabolic and tissue – Regular drinking affects the way the body metabolises alcohol and the way in which cells respond to the same level of alcohol. Chronic tolerance is lost after 3 weeks of abstinence in all drinkers. 44 44 22 7/13/22 Addiction to alcohol • Addiction is a problem in around 10% of regular drinkers • It is defined by the American Medical Association as: – Alcoholism is an illness characterised by a preoccupation with alcohol and a loss of control over its consumption, such as to lead to intoxication if drinking is begun; the condition is chronic, progressive, and has tendency to relapse. It is typically associated with physical disability and impaired emotional, occupational and/or social adjustment as a direct consequence of persistent and excessive use of alcohol • Around 1 person in a 100 becomes an alcoholic • A simple screening tool are the CAGE questions – – – – Do you feel the need to cut down your drinking? Have you got annoyed by comments about your drinking? Have you felt guilty about your drinking? Have you needed an ‘eye-opener’ in the morning? • Two ‘Yeses’ are indicative of dependency 45 45 Alcoholism I - Neurology • Wernicke-Korsakoff syndrome • Two components that may occur alone or together – Wernicke’s encephalopathy – dementia, ataxia, visual disturbances movements – Korsakoff’s syndrome – anterograde amnesia (i.e., an inability to learn new things), confabulation, language difficulties generate a bizarre story when confronted with memory loss • Cause – Chronic alcohol abusers tend to have poor diets, and hence have low intakes of thiamine (vitamin B1) – Alcohol may interfere both with thiamine uptake and adversely affect metabolic pathways that are dependent on thiamine – There may also be a genetic susceptibility • Disease course is irreversible following amnesia/dementia onset 46 46 23 7/13/22 Alcoholism II • Other neuro-degenerative disorders – Marchiafava-Bignami disease – degeneration of corpus callosum and dementia – Haemotomas – small blood clots resulting from frequent bumps to the head (occurring during intoxication) – Hepatic encephalopathy, Central pontine myelinolysis, Alcoholic cerebellar degeneration, Alcohol related dementia • Withdrawal symptoms – Mild (tremor, anxiety, insomnia) – Moderate (severe tremor, convulsions, hallucinations [typically in peripheral vision]) – Severe – AKA Delirium tremens (confusion, persecutory hallucinations, systemic circulatory problems, status epilepticus; 15% mortality if untreated) – Gets worse with repeated cycles 47 47 Alcoholism III • Other – Cardiomyopathy, myopathy, hepatitis, cirrhosis, impotence, sterility etc – Cancer of mouth, tongue, oesphagus • • 5x base rate in heavy drinkers, 8x base rate in smokers, 44x base rate in heavy drinkers & smokers Fetal alcohol syndrome • Characterised by facial abnormalities (absent philtrum, flattened bridge) and significant developmental delays of varying severity • 6% of alcoholic mothers (heavy consumption during 1st trimester) • 1200 cases (?) per year in US • Lifelong social and intellectual disability 48 48 24 7/13/22 Risk factors for alcoholism I • Several lines of evidence suggest genetic susceptibility • Increased risk in offspring of alcoholics • Risk higher if both parents alcoholic Risk the same if offspring raised by non-alcoholics • No risk (relatively) for the offspring of non-alcoholics adopted by alcoholic parents • Higher concordance in MZ than DZ twins – Individuals with alcoholic relatives show: • Less sensitivity to low levels of alcohol need to drink more to get the same effect • Abnormalities in DA receptors (wanting) • Abnormalities in 5HT metabolism (relating to heightened risk for anxiety, depression and impulsivity) 49 49 Risk factors for alcoholism II • Genes combined with… – Drinking culture • Socially sanctioned • Widespread availability (the outlet effect) – Comorbid conditions • Alcoholism tends to be comorbid with anxiety disorders such as panic attacks, OCD and phobias - self medication • Alcoholism results from an unfortunate synergy of genetic predisposition (alcohol or non-alcohol related) combined with our alcohol tolerant culture 50 50 25 7/13/22 Treatment • Pharmacological • Acute withdrawal (Benzodiazepines) • Chronic – Disulfiram (antabuse) which prevents reduction of acetaldehyde – Naltrexone which appears to be useful in preventing relapse by reducing craving (as with tobacco) • Psychological • AA, Therapy (varied), Relapse prevention training • The long-term (4 year) spontaneous abstinence rate is around 30%. Virtually no treatment appears to exceed this benchmark, although drug/psychological therapies may assist continued abstinence 51 51 Caffeine • Most adults and children consume caffeine • It is present in: – Coffee – – – – 60-280mg (per 250ml) Energy drinks 80mg (per 250ml) Tea 30-110mg (per 250ml) Cola’s 35mg (per 250ml) Chocolate 20mg (per 100g bar) • It is undoubtedly the worlds most popular psychoactive drug, hence its mention here 52 52 26 7/13/22 What are its psychological effects? • Cognitive – Decreases reaction time – Attentional effects • Increases vigilance (especially on monotonous tasks) • Benefits both endogenous (voluntary capacity to direct attention) and exogenous (ability to attend to external events) attention • Mood – Increases feelings of alertness – Increases feelings of subjective wellbeing • It exerts these effects equally in both sleep deprived and non-sleep deprived individuals • Important caveat! – There is much uncertainty as to whether the cognitive and mood effects of caffeine JUST reflect the alleviation of withdrawal symptoms. This is because almost everybody consumes caffeine. 53 53 What are its physiological effects? • Physiology • • • • Mild diuretic Increases blood pressure, heart rate At high doses, tremors, anxiety, racing heart Some evidence for adverse effects on pregnancy • How are the physiological and psychological effects exerted? • Adenosine (involved in energy metabolism) increases during the day and is elevated whilst asleep. Caffeine prevents adenosine binding to its receptor • Caffeine also interacts with GABA receptors, slowing the binding of benzodiazepines and other hypnotic agents • It indirectly modulates striatal dopamine and MAY potentiate the effects of certain addictive drugs • Is caffeine addictive? 54 54 27 7/13/22 Is it addictive? – Uhm Perhaps... • Is it abused? • In very rare instances (caffeine intoxication >1000mg/day) • It does not appear to produce a high and animals do not self administer this drug, but it is a positive reinforcer in animals and people (i.e., both like it) • Tolerance? • There is some evidence of acute tolerance but little or no evidence of chronic tolerance • Withdrawal? • Many suggest there is a withdrawal syndrome – Headache, fatigue, cognitive dulling, low mood, which are readily alleviated by consuming caffeine • This is disputed by others – Some say these symptoms are expectancy effects – A prior headache history may predict this particular symptom – Guatemala study - heavy coffee intake in kids (6x adult US consumption) followed by abrupt cessation found no withdrawal symptoms 55 55 Finally… are certain foods addictive? • It has been claimed that certain foods are‘addictive’ • Fast food (high fat/high salt or high fat/high sugar) • Hyper-processed foods (chocolate, crisps, ice cream...) • This is a very live and controversial issue – why? • It is because of blame – If the sort of foods that make people fat are addictive then if I overeat it is not my fault VS – If such foods are not addictive, then I am choosing to eat them, in which case if I overeat it is my fault • This is the same argument taken by tobacco and gun lobby of the sort “...guns don’t kill – it’s who pulls the trigger”. • This has major legal and social ramifications because if certain foods are addictive, then food manufacturers are to blame for the obesity epidemic and can be sued… 56 56 28 7/13/22 Are such foods addictive? • The US courts do not think so (McDonalds case) as in 2001 5 obese Americans took McDonalds to court on 5 counts: – – – – – • Count I alleged that McDonalds failed to adequately disclose the ingredients and/or health effects of ingesting certain of their food products with high levels of cholesterol, fat, salt and sugar; described their food as nutritious; and engaged in marketing to entice consumers to purchase “value meals” without disclosing their detrimental health effects Count II focused on marketing techniques geared toward inducing children to purchase and ingest McDonalds' food products Count III McDonalds acted at least negligently in selling food products that are high in cholesterol, fat, salt and sugar when studies show that such foods cause obesity and detrimental health effects Count IV alleged that McDonalds failed to warn the consumers of their products of the ingredients, quantity, qualities and levels of cholesterol, fat, salt and sugar content and other ingredients in those products, and that a diet high in fat, salt, sugar and cholesterol could lead to obesity and health problems Count V alleged that McDonalds acted negligently in marketing food products that were physically and psychologically addictive The case was dismissed and subsequent legislation now prevents consumers taking food manufacturers to court 57 57 Are such foods addictive? • However, a lot has changed since that court case and the science has become somewhat more persuasive – Mouse data on sugar (but...)… but not fat – Changes in brain reward areas in human obesity (contentious, not replicable) • Vicious circle models – degrading self-control • Susceptibility to addiction – Binge Eating Disorder • When it comes to social significance for research topics in the area of appetite and ingestive behaviour you cannot get more pertinent than this 58 58 29 7/13/22 Conclusion • Caffeine is probably benign with few if any negative effects • Alcohol, on the other hand, has serious adverse effects on the health of many people - but it is also very popular and is a major source of tax revenue • And what if certain types of food lead to overconsumption and obesity – this would vastly overshadow the societal costs of alcohol • So how does society balance up the costs and benefits of choice versus regulation? • Where do we draw the line between personal choice to indulge and the societal costs of that indulgence? • This question is well worth pondering as it is represents a key philosophical difference between the political left (‘nanny state’) & right (‘free to choose’) 59 59 30