Exposure to bright light is associated with positive social interaction and good mood over short time periods: A naturalistic study in mildly seasonal people

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Abstract

Bright light is used to treat winter depression and might also have positive effects on mood in some healthy individuals. We examined possible links between bright light exposure and social interaction using naturalistic data. For 20 days in winter and/or summer, 48 mildly seasonal healthy individuals wore a light meter at the wrist and recorded in real-time their behaviours, mood, and perceptions of others during social interactions. Possible short-term effects of bright light were examined using the number of minutes, within any given morning, afternoon or evening, that people were exposed to light exceeding 1000 lux (average: 19.6 min). Social interactions were labelled as having occurred under conditions of no, low or high bright light exposure. Independent of season, day, time, and location, participants reported less quarrelsome behaviours, more agreeable behaviours and better mood when exposed to high but not low levels of bright light. Given that the effects were seen only when exposure levels were above average, a minimum level of bright light may be necessary for its positive effects to occur. Daily exposure levels were generally low in both winter and summer. Spending more time outdoors and improving indoor lighting may help optimize everyday social behaviour and mood across seasons in people with mild seasonality.

Introduction

Seasonal variation in prevalence and symptom severity is a feature of several psychiatric illnesses (Fossey and Shapiro, 1992), including major depression, which is more common and often recurs in winter (Avasthi et al., 2001, Parker and Walter, 1982, Suhail and Cochrane, 1998). Winter depression is the more common variant of seasonal affective disorder (SAD; Rosenthal et al., 1984b). The Seasonal Pattern Assessment Questionnaire (Rosenthal et al., 1984a) was developed to assess the magnitude of seasonal symptom changes in SAD but has also been used to measure the wide range of seasonality in the general population (Haggag et al., 1990, Harris and Dawson-Hughes, 1993, Schlager et al., 1993). An awareness of seasonal changes in mood and behaviour is present in most people (Kasper et al., 1989b, Magnusson et al., 1997, Murray, 2003).

Feeling worse in winter is most often associated with light-related variables, such as short day length and grey cloudy weather (Kasper et al., 1989a, Kasper et al., 1989b, Schlager et al., 1993). Consistent with the idea that a relative lack of exposure to bright light may be responsible for at least some of the clinical characteristics of SAD, treatment with artificial bright light is often successful in alleviating the winter depression (Rosenthal et al., 1984b, Tam et al., 1995). The effects of bright light in patients with SAD have mostly been studied over a period of weeks. However, reports of improvement after 2–3 days, in the afternoon following morning light therapy, and after as little as one hour, do exist (Kripke et al., 1983, Rosenthal et al., 1985, Rosenthal et al., 1984b, Sher et al., 2001). Observations of the benefit of morning bright light fading later in the day or lasting only a single day also suggest that short-term exposure is sufficient for mood change to occur (Kasper et al., 1990, Kripke et al., 1983). If bright light can improve mood in patients with SAD after even a few hours, then bright light’s effects on normal mood in everyday life may also be fairly immediate.

Several studies conducted in winter at latitudes 39–60N examined the effect of light therapy on mood in healthy people. Treatment usually consisted of 2500 lux daily for various lengths of time over the course of at least a week. While some studies found that bright light could improve mood (Avery et al., 2001, Kasper et al., 1989a, Partonen and Lonnqvist, 2000), others did not (Bauer et al., 1994, Genhart et al., 1993, Rosenthal et al., 1987). Overall, these findings suggest that artificial bright light, when administered over longer time periods, may mostly benefit individuals with marked seasonality, although individuals with only mild seasonality may also show positive effects when provided with appropriate light doses. None of these studies investigated the possible short-term effects of bright light.

Despite its assumed relevance to seasonal psychopathology, data on the relation between natural light exposure and mood are scarce. In one study of young women, mood and ambient light levels were measured twice daily for 32 days and found to be positively associated (Einon, 1997). In another study, which included middle-aged men and women, mood was associated with the degree of exposure to bright light (⩾1000 lux) in the week before the two-day measuring period (Espiritu et al., 1994). Finally, in a group of elderly people, mood assessed during study intake was associated with light exposure the week after (Jean-Louis et al., 2005), possibly because exposure to bright light during this week reflected habitual exposure. Overall these findings indicate that, at least in some circumstances, an increase in natural bright light exposure might benefit mood and well-being in everyday life. However, the studies were limited because either mood was measured at a single time point only, which limits the sensitivity to detect changes in response to light (Espiritu et al., 1994, Jean-Louis et al., 2005), or light levels were not measured continuously across time, which prevents the determination of its speed of action (Einon, 1997). Studies on the relation between everyday light exposure and mood should include multiple and frequent assessments of both.

A possible effect of light on mood suggests it might also influence behaviour. We have shown that tryptophan, the precursor of serotonin, improves social behaviour along an agreeable-quarrelsome dimension in healthy people (aan het Rot et al., 2006b, Moskowitz et al., 2001). An event-contingent recording method was used which provides reliable estimates of behaviour when data are aggregated over a suitable number of days (Moskowitz, 1994). Based on recent observations in healthy volunteers that bright light exposure may affect the serotonin system within a few hours (aan het Rot et al., 2006a, Lambert et al., 2002), the present study was designed on the premise that the effects of light on everyday social behaviour and mood would resemble those of tryptophan. In mildly seasonal healthy individuals, who are sensitive to seasonal changes in natural light levels without suffering from winter depressions, ambient light levels and social interactions were measured across 20-day periods in winter and summer. Bright light exposure was hypothesized to be associated with lower levels of quarrelsome behaviours, higher levels of agreeable behaviours, and better mood. We focused on season-independent associations that might occur over short time intervals.

Section snippets

Participants

The study was approved by the Research Ethics Board of the McGill University Health Centre. All participants provided written informed consent after the study had been explained and were remunerated for time spent in the study.

The study was conducted in Montreal, Canada (near latitude 45N). Participants were recruited in winter (November–March) or summer (May–September). Advertisements including the question “Do you feel less energetic in winter than in summer?” were posted in local newspapers.

Preliminary data investigation

Evening BLE levels were more likely to be tagged than morning (t47 = −3.14, p < 0.003) and afternoon data (t47 = −3.24, p < 0.003), which were equally likely to be tagged (t47 = −1.46, p > 0.1). There were no seasonal differences in tagging (t81 = 0.10, p > 0.9).

As anticipated, BLE was higher in summer than in winter (F1, 34 = 721.79, p < 0.0001). In addition, we expected and found that the three other within-subjects factors Day of the week (F6, 278 = 22.92, p < 0.0001), Time period (F2, 93 = 358.22, p < 0.0001), and

Discussion

The present study included mildly seasonal individuals in whom ambient light levels and social interactions were recorded during 20 consecutive days in both winter and summer. This study is the first to examine possible short-term effects of bright light (⩾1000 lux) in healthy people with mild seasonality, to concurrently measure everyday light exposure and mood over multiple days, and to measure social behaviour in addition to mood as possible variables influenced by prevailing light levels.

Conclusion

The healthy, working mildly seasonal individuals who participated in the present study may often have been insufficiently exposed to bright light to ensure optimal social interaction. Above-average bright light levels were associated with lower levels of quarrelsomeness, higher agreeableness, and better mood. Especially in winter, but also on some days in summer, these participants might have benefited from additional bright light exposure, which could be derived from more outside activities or

Acknowledgements

This research was supported by a grant from the Canadian Institutes of Health Research to S.N.Y. (MOP 15005). M.a.h.R. is the recipient of a Doctoral Scholarship from the Fonds de Recherche en Santé du Québec. We are grateful to Lisa Hancock and Sarah White for their valuable assistance in the collection and processing of the social interaction data and to Francine James for help with the light meter data.

This study was presented in poster format at the Society of Biological Psychiatry 61st

References (45)

  • A. Magnusson et al.

    Internal consistency of the Seasonal Pattern Assessment Questionnaire (SPAQ)

    Journal of Affective Disorders

    (1997)
  • D.S. Moskowitz et al.

    The effect of tryptophan on social interaction in everyday life: a placebo-controlled study

    Neuropsychopharmacology

    (2001)
  • G. Murray

    The Seasonal Pattern Assessment Questionnaire as a measure of mood seasonality: a prospective validation study

    Psychiatry Research

    (2003)
  • T. Partonen et al.

    Bright light improves vitality and alleviates distress in healthy people

    Journal of Affective Disorders

    (2000)
  • N.E. Rosenthal et al.

    No mood-altering effects found after treatment of normal subjects with bright light in the morning

    Psychiatry Research

    (1987)
  • M. aan het Rot et al.

    Bright light exposure prevents mood lowering induced by acute tryptophan depletion in women with mild seasonality

    International Journal of Neuropsychopharmacology

    (2006)
  • M. aan het Rot et al.

    Social behaviour and mood in everyday life: the effects of tryptophan in quarrelsome individuals

    Journal of Psychiatry and Neuroscience

    (2006)
  • D.H. Avery et al.

    Bright light therapy of subsyndromal seasonal affective disorder in the workplace: morning vs. afternoon exposure

    Acta Psychiatrica Scandinavica

    (2001)
  • A.T. Beck et al.

    Cognitive therapy of depression

    (1979)
  • K.W. Brown et al.

    Dynamic stability of behavior: the rhythms of our interpersonal lives

    Journal of Personality

    (1998)
  • R.J. Cole et al.

    Seasonal variation in human illumination exposure at two different latitudes

    Journal of Biological Rhythms

    (1995)
  • E. Diener et al.

    The independence of positive and negative affect

    Journal of Personality and Social Psychology

    (1984)
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