Many thanks to Katie O Callaghan for writing this guest post. Katie is a final year dietetics student based in London, with a passion for evidence-based nutrition and holistic healthcare.

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Now that we have explored specific nutrients, dietary patterns and the physiological mechanisms underpinning the connection between food and mood – this article will explore the impact of different types of drinks on our mood. 

Fluid & Hydration

Adequate hydration is important for overall health and is often considered to impact cognition and concentration.

Water accounts for 55-75% of body weight and without it we could not maintain biological functions and metabolic pathways¹.

Current recommendations for daily fluid intake are 2L for women and 2.5L for men². As well as drinks – certain foods also contribute to fluid intake with many fruits, vegetables and dairy products having a high water content¹.

Assessing hydration status can be challenging due to its dynamic nature. Blood, siliva, body mass and urine can be used to estimate hydration status, or these can be used in combination, depending on the level of precision required. Urine colour can be a useful marker of hydration at home – pale straw colour urine indicates good hydration and dark coloured urine indicates underhydration ^3,4.

In terms of physical performance, even a modest decrease in hydration status can reduce exercise endurance and motivation while increasing fatigue and perceived effort ⁵.

Mild dehydration of 2% loss of body mass can  reduce cognitive performance and alertness⁶.

It has also been observed that memory, motor skills and numeric abilities decline in states of moderate dehydration¹.. However these findings have not been consistent⁵. One study found that increased water ingestion increased alertness, however had no impact on cognition⁷.

Hydration status impacts thermoregulation – the process the body uses for temperature control. Sweating has a cooling effect on the body and if fluid loss is not replaced, this can result in a state of dehydration, heat stress, loss of electrolytes and a decrease in plasma volume¹. Heat stress can be experienced by those living in hot climates, those carrying out heavy labour during hot seasons or those performing exercise. It can affect mood and increase feelings of distress⁸. Replacing lost fluids can help the body to maintain normal temperature¹.

A study carried out in endurance trained cyclists evaluated effects of prolonged exercise on cognition, alertness and heat stress. The cyclists performed two three hour cycles in a controlled laboratory environment, one with water provided prior and incrementally during the activity, and one where no water was provided. The study found that heat stress increased in cyclists performing both tests – but significantly more so when fluids were not replaced, demonstrating that fluid replacement and hydration can reduce heat stress.

However the study found no significant difference between cognitive performance in both experiments, indicating that hydration status of the subjects had no significant effect on cognition. It is possible that this is because the participants were well trained and accustomed to these conditions, meaning that perhaps this evidence is not relevant for those not similarly trained⁹. 

Summary: Aim for at least 2-2.5l of fluids daily to maintain overall health, and don’t forget that foods high in fluid also contribute to fluid intake. Maintaining hydration leads to reduced risk of heat stress. Adequate hydration, although not consistently, has also shown improved cognition, alertness, short-term memory, numerical abilities and concentration in some individuals. 

Caffeine

Caffeine is a plant based psychoactive substance and the most commonly consumed stimulant in the world¹⁰. The European Food Safety Authority report that caffeine intakes of up to 400mg for healthy adults and 200mg for pregnant women are generally safe. In Europe, adults consume approximately 180mg of caffeine per day. In the UK and Ireland the biggest contributor to caffeine intake is tea¹¹.Other common sources of caffeine are chocolate, coca cola, energy drinks and of course, coffee. 

Approximate caffeine content of these are as follows:

• Tea: 75mg 
• Instant coffee: 100mg
• Filter coffee: 140mg
• Single espresso: 75mg
• Regular americano/cappuccino/latte: 150mg
• Decaffeinated coffee: 7mg
• Cola/diet cola: 40mg
• Energy drink: 60mg
• 50g milk chocolate: 25mg
• 50g dark chocolate: 50mg

In recent years there have been various health claims and headlines in the media about caffeine’s effect on our physical health. But what about our mental health?

As discussed above – poor hydration status can lead to impaired cognitive function and cause mood disturbances.

It is a myth that moderate consumption of tea or coffee is dehydrating.

Of the available evidence it can be observed that although caffeine consumption increases urine output by the kidneys, moderate consumption of 1.4-6mg/kg/day (98-420mg -approximates 1-2.5 tall Americanos for a 70kg person) does not lead to decrements in hydration status ¹⁰. This is partially due to the fluid content of the drink off-setting any mild increase in urine output.

One study did however find an association between caffeine intake and hydration status- but this study used significantly higher caffeine intakes of 8.75mg/kg/day (612mg/day- approximately 4 tall americanos for 70kg individual)¹². Therefore, beverages containing caffeine are considered to contribute to overall fluid intake.

Moderate caffeine intake is associated with notable improvements in alertness, vigilance, enhanced cognitive function and mood as well as reduced perception of fatigue ^10,13.

Studies which have assessed the effect of caffeine in states of sleep deprivation have shown improvements in learning ability and memory function after approximately 200mg of caffeine (approximately 1 mug of brewed coffee or 1 larger americano) ¹³. However one study found adverse effects of caffeine in sleep-deprived participants¹⁰.

Numerous studies found consistent patterns of elevated mood after caffeine intakes of up to 450mg¹⁰. Regular consumers are seen to gain greater mood and cognitive effects than those who do not habitually use caffeine. It is debated that such differences could be due to withdrawal alleviation¹⁰.

Caffeine withdrawal can be observed after approximately 24-48hours, in those who consume caffeine on a daily basis, with symptoms of low mood, headache, fatigue  and poor concentration observed ^14,15.

Anxiety and sleep behaviours and are widely considered to be influenced by caffeine intake. Depression, anger and risk-taking behaviours are also proposed to be associated with consumption. A systematic review carried out in 2017 addressed whether caffeine caused adverse effects on a variety of outcomes, including behaviour. Of the examined evidence it was concluded that most adults who consume up to 400mg of caffeine daily (approximately 2.5 tall americanos) are unlikely to experience adverse physical or behavioural effects^16,17. 

However, caffeine tolerance is individual with some being more sensitive that others to its effects.

Some studies showed significant increases in measures of anxiety at intakes lower than 400mg, especially in those who generally experience anxiety^16,18. Studies using higher doses, over 400mg of caffeine show significant increases in measures of anxiety¹⁹. Doses over 400mg of have also shown to have an adverse effect on sleep patterns in sensitive individuals or in those who are prone to sleep disturbances¹⁹. Even for those who don’t feel that caffeine impacts their ability to fall asleep, it is likely to impact sleep quality – so it is best to consume our last caffeinated drink 6-12 hours before bed-time²⁰

Most clinical studies found no associations between depression and caffeine consumption with 3 studies actually showing some improvements in depression scores at intakes between 150-270mg¹⁶. An observational study examined depression risk in a group of adult women. They compared two groups, one with an average daily caffeine intake of 550mg and one with an average daily intake of less than 100mg, with no symptoms of depression at baseline. The study found no increased risk of depression after a 10 year follow up. However, because of the nature of the study, other lifestyle factors for this cannot be excluded²¹.

In terms of other mood disturbances, it has also been reported that caffeine leads to reduced relaxation²². Higher intakes of 1200mg can be associated with negative mood disturbances and feelings of anger (8 tall americanos), so it may be worth avoiding excessive intakes²³.

Research also suggests that tolerance to caffeine increases with time and exposure with ergogenic effects being still seen, but to a lesser degree, after consistent daily exposure²⁴. Those who have genetic predispositions or those who do not habitually consume caffeine are observed to report behaviour or mood changes bellow 400mg¹⁷. It appears that the effects of caffeine are dose and person specific with different individuals displaying varying behavioural symptoms depending on their habitual mood and unique sensitivity to its effects. 

Summary: Moderate consumption of caffeine (i.e.  400mg per day for adults without underlying anxiety) does not appear to adversely impact  mood. Moderate caffeine intake can also improve alertness, cognition and improve memory in states of sleep deprivation. Higher intakes can lead to increased anxiety possibly aggression. 

Alcohol

Alcohol, like caffeine, is considered to be a lifestyle drug. Although commonly considered a stimulant due to its association with elevated mood states, these effects are mostly short lived.

Alcohol is classified as a depressant as it ultimately acts as a sedative by suppressing the central nervous system ^{25, 26}. 

Current UK recommendations suggest that in order to reduce health risks associated with alcohol we should consume no more than 14 units of alcohol per week. It is also recommended that these units are spread throughout the week and allow several alcohol free days²⁷.

The Irish low-risk alcohol guidelines advise men to limit their intake to 17 standard drinks per week, and no more than 11 standard drinks per week for women. 

An estimated 27% of UK drinkers report regular binge drinking and in Ireland over half of drinkers report drinking in a harmful way, with 34% reporting that they ‘binge’ drink on a typical drinking occasion^28,29,30. Alcohol guidelines often highlight risks to our physical health, but research shows that alcohol can also affect our mood and mental health.

Alcohol use is highly correlated with severe mental health disorders and those with certain psychiatric diagnoses are more likely to be alcohol dependent than the general population³¹.

Most of the available evidence examines excessive drinking related to alcohol dependency and addiction. Studies of less extreme usage such as risky or harmful drinking are rare³². 

Excessive alcohol consumption is associated with B vitamin deficiencies, which can influence mood and brain function and could lead anxious and depressive symptoms.

Vitamin B6 is necessary for tryptophan to pass into the brain to allow the synthesis of serotonin, a neurotransmitter associated with feelings of happiness, and vitamin B6 deficiency can reduce the rate of serotonin synthesis³³. Vitamins B12, B9, B6 and B2 are essential cofactors for the synthesis of other neurotransmitters such as dopamine, serotonin, γ-aminobutyric acid (GABA), noradrenaline which have also demonstrated an association with mood ^34.35. For more information about the impact of nutrients on our mood, check out part 1 of this series. 

Excessive alcohol intake is associated with increased oxidative stress and the over production of inflammatory markers which may exacerbate feelings of anxiety and/or depression the pathways for this are discussed in part 2 of this series³⁶.

From the body of available evidence, it is clear that alcohol problems and depression and anxiety are highly correlated³¹.

However, what is not clear is whether depression and anxiety lead to problem drinking or problem drinking leads to depression and anxiety. Research in the UK found that such conditions are most commonly found in heavy drinkers, and heavy drinking is most common in those with anxiety and depression²⁸. More research is warranted, however studies of this nature are difficult to design and it is difficult to rule out other influences and casualties.

Alcohol is often used to relieve anxiety, feelings of depression and alter mood states. A recent survey in the UK reported that 88% of people drank alcohol to relax. Others reported that it made them feel more confident, less inhibited and happier. Approximately 45% said it made them feel less anxious and 30% said it made them feel less depressed³¹. 

Alcohol down-regulates excitatory neurotransmitters, meaning it can reduce neural signalling, whilst having an increased effect on inhibitory neurotransmitters, potentially blocking or reducing electrical signalling within the central nervous system²⁶.

Underlying anxiety can lead to increased alcohol use, and increased alcohol use can result in elevated anxiety³¹.

Low to moderate doses of alcohol are shown to temporarily reduce or mask feelings of anxiety³⁷. This can lead to depletion of brain neurotransmitters which the brain uses to naturally reduce these feelings – which could mean larger quantities are needed to achieve the same reduction of anxiety. Chronic or prolonged exposure can lead to increased anxiety, especially in individuals with pre-existing anxiety conditions³⁷.

A similar cyclical pattern can be observed with alcohol and depression. Alcohol exposure can significantly reduce the neurotransmitter serotonin, which is also implicated in depression³¹. As serotonin becomes more depleted, it’s possible that alcohol can be used to deal with negative mood effects.

Drinking alcohol is known to have a wide range of behavioural effects, many of which are difficult to predict and are largely individualised with some becoming loud or aggressive, and others becoming withdrawn. Its interactions with the hippocampus can lead to alcohol induced memory lapses and it interaction with other brain regions impairs judgement and concentration²⁵. 

Regular drinking can increase tolerance to alcohol meaning a higher blood alcohol concentration is required to feel the effects, possibly leading to increased consumption³⁸. 

Drinkers can experience negative effects in the days preceding heavy drinking. This is commonly known as a hangover and is experienced as mental and physical symptoms as blood alcohol concentration approaches zero. This is commonly involves impaired attention span, memory and reaction times³⁹.

One study demonstrated reduce mood state on the day following drinking, by decreased feelings of happiness being reported by participants⁴⁰. After periods of excessive drinking or when those who are alcohol dependant stop, alcohol withdrawal may occur. This may result in overactivity of the nervous system leading to a series of unpleasant symptoms including a tremor, sweating, anxiety and occasionally hallucinations²⁵.

There is little evidence on the effects of moderate drinking on mental health and whether there are benefits to light drinking.

Alcohol is used in many social situations and commonly involved in celebration and it is not clear whether it is universally associated with detrimental effects on mental health. There is some evidence to suggest that drinking in small amounts (less than 7 units per week) can elicit positive emotional or mental effects. However this evidence is criticised for its lack of consideration for other lifestyle factors which could contribute to these conclusions⁴¹.

Summary: Excessive drinking can lead to B vitamin deficiencies, increased inflammation and oxidative stress which can impact our mood. Alcohol can initially reduce feelings of anxiety and depression, but when used to deal with underlying problems it can cause destructive cyclical patterns through interfering with neurotransmitter pathways which may be damaging to our mental health. The evidence for alcohol having a long term positive effect is limited. 

Click here to read Food & Mood – Part 1: Diet Patterns & Important Nutrients

Click here to read Food & Mood – Part 2: Physiology

 References

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