Tiredness

Summary of the Study: Caffeine and Mood

This study investigated the relationship between caffeine consumption and mood in a real-world setting, utilizing data from 115 participants in the first study and 121 in the second. Here’s a breakdown of the key aspects:

Methods:

Data Collection: Participants used surveys triggered randomly throughout the day (with a 90-minute gap) to report caffeine intake, mood, tiredness, sleep, social context, and daily routines.
Baseline measures: Researchers collected data on typical caffeine intake, dependence, depressive symptoms, anxiety, and sleep quality, alongside daily sleep diaries.
Analysis: Multilevel models were used to analyse the data, controlling for factors like sleep and examining potential moderators (time of day, tiredness, social setting, individual traits).

Positive Effect Boost: Caffeine consumption was consistently linked to higher momentary positive affect (feelings of enthusiasm,happiness,and contentment) in both studies.
Limited Negative Affect Impact: Caffeine had a small and inconsistent effect on negative affect, reducing sadness and upset only in the second study, and not worry.
Timing Matters: The positive mood boost was strongest within the first 2.5 hours after waking,with a smaller increase around 10-12.5 hours post-awakening. No time-of-day effects were found for negative affect.
Individual Traits Don’t Matter Much: Factors like caffeine dependence, habitual intake, depression, anxiety, or sleep quality did not significantly alter the relationship between caffeine and mood.
Context is Key: Being tired enhanced caffeine’s positive effects, while being around others reduced them.

Conclusions:

Caffeine reliably enhances positive mood, particularly in the morning.
Situational factors (tiredness, social context) have a greater influence on caffeine’s mood-boosting effects than individual characteristics.
The morning effect might potentially be due to habitual consumption or circadian rhythms.
The study provides real-world evidence supporting caffeine’s mood-enhancing properties.

Limitations:

Relied on self-reported data. Sample was young and predominantly female.
Lack of precise caffeine timing information.
No assessment of chronotype (morning/evening preference).

Future Research:

The authors suggest future studies should investigate:

The impact of first daily caffeine consumption.
Withdrawal symptoms.
* Objective measures of circadian rhythms.