Differential association between affect and somatic symptoms at the between- and within-individual level

Area of Science:

• Psychology
• Psychosomatic Medicine
• Affective Science

Background:

• Affective states and somatic symptoms are closely linked, with prior research often suggesting a causal link from affect to symptoms.
• Cross-sectional studies indicate higher negative affect correlates with more somatic symptoms, but these findings may not apply at the individual level.
• Diary studies offer insights into within-individual processes, differentiating population-level findings from personal experiences.

Purpose of the Study:

• To investigate the associations between positive affect (PA), negative affect (NA), and somatic symptoms.
• To differentiate between-subject (between-person) and within-subject (within-person) associations.
• To explore the temporal dynamics, including lagged effects, of affect on somatic symptoms.

Main Methods:

• Utilized diary data from an online study ('HowNutsAreTheDutch') with 586 participants.
• Collected data three times daily for 30 consecutive days, totaling 28,264 questionnaires.
• Employed mixed-effects linear modeling to analyze contemporaneous and lagged associations.

Main Results:

• Between-subjects: Negative affect showed a significant positive association with somatic symptoms (B=.60, p<.001); positive affect showed a smaller negative association (B=-.14, p=.062).
• Within-subjects: Positive affect had a stronger negative association with somatic symptoms (B=-.33, p<.001) than negative affect (B=.13, p<.001).
• Lagged analysis indicated previous-day positive affect negatively predicted somatic symptoms (B=-.05, p=.001).

Conclusions:

• Negative affect is more influential for between-person symptom level differences, while positive affect is more critical for within-person symptom fluctuations.
• Findings suggest a potential causal role for positive affect, as increased PA was followed by decreased somatic symptoms after 24 hours.
• This study highlights the importance of distinguishing between- and within-individual processes and the utility of diary methods in affective science.