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. Author manuscript; available in PMC: 2013 Jun 18.
Published in final edited form as: Psychiatry Res. 2006 May 24;143(1):35–42. doi: 10.1016/j.psychres.2005.08.018

Light exposure is related to social and emotional functioning and to quality of life in older women

Michael A Grandner a,b,*, Daniel F Kripke b, Robert D Langer c
PMCID: PMC3685148  NIHMSID: NIHMS479297  PMID: 16725207

Abstract

While there are data supporting the use of light in clinical populations, there has been less investigation of relationships among light and psychological variables in non-clinical samples. Subjects were 459 ethnically diverse women (mean age 67.68) recruited as part of the Women's Health Initiative. Light exposure and sleep were measured with an Actillume wrist actigraph. Subjects completed questionnaires, investigating Social Support, Social Functioning, Social Strain, Quality of Life, Satisfaction with Life, Emotional Well-being, Optimism, Negative Emotional Expressiveness, and Role Limitation Due to Emotional Problems. Significant partial correlations (controlling for age, education and ethnicity) were found between mesor light exposure and Social Functioning, Quality of Life, Satisfaction with Life, and Emotional Well-Being. Quality of Life and Satisfaction with Life were also found to be significantly correlated with morning light. The most parsimonious model to account for the variance shared between mesor light and the predictors included only Quality of Life. The variance shared between mesor light exposure and social and emotional functioning could be subsumed under the variance shared between mesor light exposure and Quality of Life. Increased light exposure is related to improved quality of life and social and emotional functioning. Increased light exposure is related to improved quality of life and social and emotional functioning.

Keywords: Phototherapy, Circadian rhythm, Interpersonal relations, Emotional disturbances, Sleep

1. Introduction

Light (or its lack) may be associated with both seasonal (Tam et al., 1995) and nonseasonal (Kripke, 1998) affective illness. Light functions as a zeitgeber (timegiver) in the human circadian system. Disruptions of circadian rhythms have been implicated in the pathogenesis of affective illness (Kripke et al., 1992). Bright light therapy has become a treatment of choice for seasonal affective disorder (SAD) (Lam and Levitt, 1999) and also may be recommended for depression that is not seasonal (Kripke, 1998; Tuunainen et al., 2001; Golden et al., 2005).

Fewer studies have examined the relationship between light and depression in the general population. One group (Kohsaka et al., 1999) found that moderately bright light (1000 lux) increased sleep quality and alertness in eight healthy elderly women studied in the fall months. Another group (Partonen and Lonnqvist, 2000) studied bright light administered to healthy people during the winter in southern Finland. This investigation of 160 office workers indicated that bright light reduced depressive symptoms and increased vitality and quality of life. Brunn-strom et al. (2004) found that improving lighting conditions significantly improved ratings of quality of life among visually impaired participants in Sweden. However, other studies (Kasper et al., 1990; Genhart et al., 1993) failed to demonstrate benefits in healthy people.

In addition to studies of the benefits of light in the general population, some research has investigated the importance of natural versus artificial light. Natural sunlight may be a more powerful mechanism for entrainment of circadian rhythms than ordinary artificial light (Lewy et al., 1980) because outdoor light is often brighter. A 1-h morning walk for 1 week in natural lighting was shown to alleviate seasonal affective disorder (SAD) symptoms versus placebo (Wirz-Justice et al., 1996). Other studies also suggest that morning light may be particularly beneficial in alleviating depressive symptoms (Clodoré et al., 1990; Eastman et al., 1998; Lewy et al., 1998; Terman et al., 1998).

Degree of behavioral and affective sensitivity to changing seasonal light patterns has been positively related to neuroticism (Murray et al., 1995; Jang et al., 1997). Those with high seasonality exhibit a strong emotional reaction to changing weather (Rosenthal et al., 1987; Albert et al., 1991; Molin et al., 1996) and demonstrate increased mood variability and sensitivity to other zeitgebers such as social cues (Reid et al., 2000). Patients with SAD may experience a greater number of negative life events and decreased social support (Michalak et al., 2004b). Additionally, SAD patients have reported low ratings of quality of life (Partonen and Lonnqvist, 1996; Michalak et al., 2004a) which may present in a seasonal pattern (Michalak et al., 2005). A more direct relationship between ambient, environmental light and social and emotional functioning, however, has not been specifically investigated.

Data from the Women's Health Initiative (WHI) provided an opportunity to examine relationships of habitual light exposure to social and emotional functioning, and quality of life, in postmenopausal women (Matthews et al., 1997). Light was measured using a wrist actigraph. Quality of life and social and emotional functioning variables were measured using questionnaires. It was hypothesized that (1) increased light exposure would be related to improved quality of life and social and emotional functioning, (2) advanced phase (earlier timing) of the light exposure is related to improved quality of life and social and emotional functioning, and (3) morning light is more predictive of the benefits of light than day-long exposure.

2. Methods

2.1. Subjects

Subjects were 459 women recruited as part of an ancillary study of the Women's Health Initiative (WHI), a large, multi-site, longitudinal study of health in postmenopausal women; a description of methods and rationale can be found in Matthews et al. (1997) and WHI Study Group (1998). All women were post-menopausal (mean age 67.68, S.D. 7.86, range 50 to 81). Recruitment emphasized ethnic diversity. Several previous reports of data from these subjects have appeared (Jean-Louis et al., 2000, 2001a,b; Tuunainen et al., 2001; Wallace-Guy et al., 2002; Youngstedt et al., 2004).

2.2. Actillume

Light recordings were made using an Actillume™ wrist actigraph worn for 1 week. All records were hand-scored for sleep, with the assistance of a validated algorithm (Jean-Louis et al., 2001a,b). The Actillume photometer measured lux and physical activity each second, and then averaged across 1-min epochs. Lux values were log-transformed (with logarithms below 0 recoded as 0), and cosine-fitted. The mesor (fitted cosine mean) and acrophase (fitted cosine peak) of these log scores, as well as mesor of physical activity measurements, were computed using ACTION 3 software (Ambulatory Monitoring Inc., Ardsley, NY). Acrophase deviation from the group median was computed by taking the absolute value of each acrophase difference from the group median. Morning light was computed as mean log lux during the first 4 h after awakening, usually involving most of the awake hours before noon. Phase–response curve data suggest that this would cover the most sensitive portions of the advance portion of the phase-response curve (except those during sleep).

2.3. WHI questionnaires

Social and emotional functioning were assessed using self-report questionnaires designed for use as part of the WHI (Matthews et al., 1997; WHI Study Group, 1998). These measures were designed by national committees, based on a review of contemporary psychometric methods and are thought to be reliable and valid (Matthews et al., 1997; Anderson et al., 2003; Langer et al., 2003). Questionnaires were administered by staff during subjects’ visits to WHI offices.

Social Support was measured as the sum of the scores of responses to the question: “How often are these kinds of support available?” The following possible responses were each measured on a 1 to 5 Likert scale and summed: “Someone to listen when need to talk,” “Someone to give good advice,” “Someone can take to the doctor,” “Someone to have a good time with,” “Someone to help understand a problem,” “Someone to help with daily chores,” “Someone to share private worries/fears,” “Someone to do something fun with,” and “Someone to love you/make you feel wanted.” Thus possible scores ranged from 5 to 45.

Social Functioning was measured by averaging two ratings (on a 0–100 scale), where the subjects reported the degree to which physical or emotional problems interfere with social functioning by determining extent and frequency.

Social Strain was measured as the sum of the following items measured on a 1 to 5 Likert scale: “Number of people who get on nerves,” “Number of people who ask too much,” “Number of people who exclude you,” and “Number of people who try to coerce.”

Quality of Life was measured using a 1 to 10 scale that simply asks respondents to “rate the quality of your life (10 being highest),” and Satisfaction with Life was measured using a 1 to 10 scale that simply asks respondents to “rate your satisfaction with the quality of your life (10 being highest).”

Emotional Well-being was measured on a 0–100 scale (100 reflecting highest well-being) computed from variables asking, “Have you been very nervous,” “Felt down in the dumps,” “Felt calm and peaceful,” “Felt downhearted and blue,” and “Have you been happy?”

Optimism was measured as the sum of the following items measured on a 1 to 5 Likert scale (5 being highest): “Usually expect the best,” “Expect something that can/will go wrong (reverse-scored),” “Always hopeful about future,” “Expect more good things than bad,” “Hardly ever expect things to go my way (reverse-scored),” and “Rarely count on good things happening (reverse-scored).”

Negative Emotional Expressiveness was measured as a 1–5 rating scale (5 representing greatest amount of expression of negative emotions) averaged from following items: “Usually people around me know when I'm angry,” “You can tell from my facial expressions how I'm feeling,” “I express disappointment,” and “If angered, I may cause a scene in a public place.”

Role limitation due to emotional problems was measured on a 0–100 rating scale (100 reflecting greatest impairment) computed from items that asked how emotional problems have affected functioning in terms of time spent, amount of accomplishment, and amount of care given to work.

2.4. Data analysis

The relationships among light variables, quality of life and social and emotional variables were investigated by using partial correlations (controlling for age, education level, and ethnicity). Six ethnic groups were entered as pseudo-variables of 0 (absent) or 1 (present) for White, Black, Asian, Hispanic, Native American and Other. Because outdoor exercise effects and outdoor light effects could be confounded, correlations of emotional variables with light exposure were also controlled for the mesor (daily mean) of Actillume wrist activity. To ascertain any added benefit of morning light, hierarchical regression models were used (first entering age, education and ethnicity covariates, then entering mesor light, and then morning light). Finally, a stepwise regression procedure was employed to investigate the relative variance contributions of the quality of life, social and emotional variables to light exposure.

3. Results

3.1. Subject characteristics

The sample was ethnically diverse, with 68.2% reporting being White, 13.6% Hispanic or Latino, 10.1% African-American or Black, 4.5% Asian or Pacific Islander, 1.6% Other, and 1.3% American Indian or Alaskan Native. Additionally, a wide range of educational backgrounds was represented (highest level achieved): 0.2% didn't go to school, 0.9% grade school (1–4 years), 0.9% grade school (5–8 years), 4.0% some high school, 11.2% high school diploma or GED, 10.1% vocational or training school, 35.3% some college or associate degree, 12.3% college graduate or baccalaureate degree, 11.9% some graduate or professional education, 11.6% master's degree, and 0.7% doctoral degree.

Actillume recordings were taken a mean of 290 days following questionnaire administration (range 21 to 1819 days). Correlation strength was not found to be systematically weaker in subjects for whom Actillume recordings were taken after a longer period following questionnaire administration versus a shorter time interval.

Overall mean and standard deviations of the variables are reported in Table 1. Because some responses were missing, N values are also reported (for example, almost half of the subjects were never laboriously scored for morning mean lux).

Table 1.

Means and standard deviations for light, social and emotional functioning variables

Variable N Mean S.D.
Mesor log10[Lux] 436 1.10 0.27
Morning light Mesor log10[Lux] 271 1.77 0.47
Acrophase deviationa 437 00:03:09 00:54:35
Social Support 434 35.55 8.12
Social Functioning 445 86.57 21.29
Social Strain 442 6.48 2.61
Quality of Life 446 8.24 1.65
Satisfaction with Life 446 8.10 2.06
Emotional Well-being 442 79.75 14.98
Optimism 441 23.73 3.58
Negative Emotional Expressiveness 446 2.81 0.63
Role Limitation Due to Emotional Problems 444 82.88 31.15
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a

Represented as clock time (hh:mm:ss).

3.2. Partial correlations

Partial correlations between light and social and emotional variables are reported in Table 2. Significant partial correlations (controlling for age, education and ethnicity) were found between mesor light exposure and Social Functioning, Quality of Life, Satisfaction with Life, and Emotional Well-Being. Quality of Life and Satisfaction with Life were also found to be significantly correlated with morning light.

Table 2.

Partial correlations between light variables and social and emotional variables, controlling for age, education and ethnicity

Variable Mesor light
 P Morning light
 P
N r N r
Social Support 414 0.086 NS 252 0.091 NS
Social Functioning 422 0.158 ≤0.005 259 0.107 NS
Social Strain 421 –0.030 NS 258 0.035 NS
Quality of Life 422 0.185 ≤0.0005 260 0.216 ≤0.001
Satisfaction with Life 422 0.134 ≤0.05 260 0.154 ≤0.01
Emotional Well-being 421 0.128 ≤0.05 256 0.113 NS
Optimism 421 0.062 NS 256 0.098 NS
Negative Emotional Expressiveness 422 –0.057 NS 260 0.001 NS
Role Limitation Due to Emotional Problems 422 0.094 NS 259 0.076 NS
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Physical activity (Actillume activity mesor) was significantly correlated with light mesor (r =0.293, P<0.0005). When correlations were repeated adding physical activity as a covariate, the strength of the correlations declined overall, but direction did not. These values can be seen in Table 3. Only the correlation with Satisfaction with Life no longer met significance criteria, suggesting that a notable portion of the variance shared between light and Satisfaction with Life might be confounded with affects of outdoor physical activity.

Table 3.

Partial correlations between light variables and social and emotional variables, controlling for age, education, ethnicity and physical activity measured by the Actillume

Variable Mesor light
 P Morning light
 P
N r N r
Social Support 413 0.081 NS 251 0.088 NS
Social Functioning 421 0.117 ≤0.05 258 0.093 NS
Social Strain 420 –0.011 NS 257 0.042 NS
Quality of Life 421 0.145 ≤0.005 259 0.193 ≤0.005
Satisfaction with Life 421 0.093 NS 259 0.141 ≤0.05
Emotional Well-being 420 0.126 =0.01 255 0.110 NS
Optimism 420 0.014 NS 255 0.084 NS
Negative Emotional Expressiveness 421 –0.022 NS 259 0.014 NS
Role Limitation Due to Emotional Problems 421 0.057 NS 258 0.064 NS
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No significant partial correlations were found between light acrophase or acrophase deviation (sample median 13:44:22) and any social or emotional variables. However, acrophase deviation was significantly correlated with quality of life (partial r=–0.132, P≤0.01, n=423) and satisfaction with life (partial r=–0.135, P≤0.005, n=423), indicating that phase deviation was negatively associated with global quality of life.

3.3. Mesor versus morning light

Hierarchical linear model comparisons were used to ascertain whether the observed correlations between morning light and both Quality of Life and Satisfaction with Life describe shared variance unique to morning light (after controlling for mesor light). In the case of satisfaction with life, no significant portion of unique variance was explained by morning light, though the significant unique variance of quality of life was contributed by morning light (this analysis was limited only to subjects for whom morning light data were obtained).

For Quality of Life, a model that included demographic covariates (age, education and ethnicity) and mesor light accounted for a significant amount of variance ( F(9,401)=4.819, P≤0.0005, adjusted R2=0.077), and a significant gain was made with the inclusion of morning light (partial F(1400)=5.760, P≤0.05, R2 change=0.013). Thus, the overall model including morning light was significant ( F(10,400)=4.965, P≤0.0005).

Similar results were shown with Satisfaction with Life. A model that included demographic covariates (age, education and ethnicity) and mesor light accounted for a significant amount of variance ( F(9,401)=3.954, P≤0.0005, adjusted R2=0.061), and a significant gain was made with the inclusion of morning light (partial F(1,400)=4.799, P≤0.05, R2 change=0.011). Thus, the overall model including morning light was significant (F(10,400)=4.072, P≤0.0005).

3.4. Shared variance among predictors

A stepwise regression procedure was used to ascertain whether the correlations between mesor light and social and emotional functioning variables were describing shared variance that is unique to each predictor or is shared among them. The regression was structured such that the dependent variable was mesor light, and the independent variables were entered. First, age, education and ethnicity were entered, and next, the variables that were shown to have correlated with mesor light were entered in a stepwise procedure.

The most parsimonious model that accounted for the variance shared between mesor light and the predictors (overall F(9,416)=7.912, P<0.0005) included only Quality of Life (B=0.028, SE=0.008, t=3.756, P<0.0005). The variance shared between mesor light exposure and both social and emotional functioning was subsumed under the variance shared between mesor light exposure and Quality of Life. To further investigate this relationship, the stepwise regression was repeated, this time including just Quality of Life and an ordinal income variable as predictor variables (controlling for age, ethnicity and education), so that it could be ascertained whether Quality of Life contributed variance over and above income. Indeed, the outcome of this analysis was similar, such that the most parsimonious model that accounted for the variance shared between mesor light and the predictors (overall F(9,409)=8.277, P<0.0005) included only Quality of Life (B=0.032, SE=0.008, t=4.138, P<0.0005) in addition to the entered demographic variables.

Further analysis showed that all of the social and emotional variables correlated significantly with Quality of Life, except for Negative Emotional Expressiveness. Partial correlations (controlling for age, education and ethnicity are reported in Table 4).

Table 4.

Partial correlations between quality of life and social and emotional variables, controlling for age, education and ethnicity

Variable N r P
Social Support 420 0.517 <0.0005
Social Functioning 431 0.414 <0.0005
Social Strain 428 –0.319 <0.0005
Satisfaction with Life 432 0.819 <0.0005
Emotional Well-being 428 0.546 <0.0005
Optimism 427 0.470 <0.0005
Negative Emotional Expressiveness 432 0.005 NS
Role Limitation Due to Emotional Problems 430 0.256 <0.0005
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4. Discussion

The present study investigated correlates of light exposure in a diverse sample of postmenopausal women. The hypotheses were partially supported: (1) increased light exposure is related to improved quality of life and social and emotional functioning, (2) morning light exposure is related to improved quality of life and social and emotional functioning, and (3) morning light is more predictive of the benefits of light than all-day exposure.

Previous studies have demonstrated mixed results regarding the psychological effects of light in non-clinical samples, with both positive (Kohsaka et al., 1999; Partonen and Lonnqvist, 2000; Brunnstrom et al., 2004) and negative findings (Kasper et al., 1990; Genhart et al., 1993). The current results support a relationship, demonstrating that increased light, especially in the morning, may be related to improved social and emotional functioning and subjective quality of life.

In relation to social and emotional functioning, while there has been a great deal of research on the role of light on circadian rhythms (Czeisler, 1995) and depression (Tuunainen et al., 2001) and social factors in the entrainment of circadian rhythms (Ehlers et al., 1988; Monk et al., 1990; Elmore et al., 1994), less attention has been paid to the unique contribution of light to social and emotional functioning.

Reid et al. (2000) studied the differential sensitivity to external (i.e., social) zeitgebers on mood fluctuations for subjects who demonstrate varying degrees of seasonality of mood. Results demonstrated that highly seasonal individuals were more responsive to external zeitgebers and had more pronounced mood cycling. These findings, along with the present results, support the importance of social situations possibly mediating the relationship between circadian rhythms, light and mood.

Highly seasonal individuals have also demonstrated emotional disturbances (Murray et al., 1995; Jang et al., 1997). Since the mechanisms underlying these seasonal relationships may be related to changes in light exposure, the present study further explores this idea by studying relationships between light exposure and emotional variables in a non-clinical sample.

The present study contributes by examining the specific relationships among light and social and emotional functioning, domains that have not previously been investigated in diverse samples studied year round. While the reported benefits of bright light in non-clinical samples have been mixed, the current results suggest that light may have at least small benefits for undiagnosed samples. In addition, this study explores the possible added benefit of morning light.

Overall, morning light appears to have marginal importance over and above all-day light. These results suggest that although morning light may be related to overall subjective quality of life ratings, it may not have specific benefit in the domains of social and emotional functioning.

There are several important limitations to this study. First, due to its correlational nature, no causal relationships can be inferred. The causal mechanisms of the relationship between light and quality of life and social and emotional functioning may be bidirectional in nature or follow complex pathways, such that those who receive more light will experience improvements in functioning and, reciprocally, those with better functioning may receive more light. The additional caveat of the importance of morning light may add to the complexity of this relationship.

Another limitation of this study was that although the sample was relatively large and diverse, it consisted only of postmenopausal women volunteers of the WHI. Results may not be generalizable to the whole population.

A third limitation of the study is that the goal of the WHI was not to evaluate the relationship between light and biopsychosocial factors. Thus, data collection was not designed for this purpose, and some measures may not have been optimal for these purposes. The intervals between collection of the questionnaires and the light measurements were certainly too long to optimally assess the relationships.

Further research should aim to extend these findings by (1) exploring additional biopsychosocial correlates of light exposure and timing and (2) extending the current findings into a more generalizable sample.

References

  1. Albert PS, Rosen LN, Alexander JR, Rosenthal NE. Effect of daily variation of weather and sleep on seasonal affective disorder. Psychiatry Research. 1991;36:51–63. doi: 10.1016/0165-1781(91)90117-8. [DOI] [PubMed] [Google Scholar]
  2. Anderson GL, Manson J, Wallace R, Lund B, Hall D, Davis S, Shumaker S, Wang C-Y, Stein E, Prentice RL. Implementation of the women's health initiative study design. Annals of Epidemiology. 2003;13:S5–S17. doi: 10.1016/s1047-2797(03)00043-7. [DOI] [PubMed] [Google Scholar]
  3. Brunnstrom G, Sorensen S, Alsterstad K, Sjostrand J. Quality of light and quality of life–the effect of lighting adaptation among people with low vision. Ophthalmic Physiological Optics. 2004;24:274–280. doi: 10.1111/j.1475-1313.2004.00192.x. [DOI] [PubMed] [Google Scholar]
  4. Clodoré M, Foret J, Benoit O, Touitou Y, Aguirre A, Bouard G, Touitou C. Psychophysiological effects of early morning bright light exposure in young adults. Psychoneuroendocrinology. 1990;15:193–205. doi: 10.1016/0306-4530(90)90030-d. [DOI] [PubMed] [Google Scholar]
  5. Czeisler CA. Ciba Foundation Symposium: Circadian Clocks and Their Adjustment. 1st ed. John Wiley and Sons; New York: 1995. The effect of light on the human circadian pacemaker. pp. 254–302. [DOI] [PubMed] [Google Scholar]
  6. Eastman CI, Young MA, Fogg LF, Liu L, Meaden PM. Bright light treatment of winter depression. Archives of General Psychiatry. 1998;55:883–889. doi: 10.1001/archpsyc.55.10.883. [DOI] [PubMed] [Google Scholar]
  7. Ehlers CL, Frank E, Kupfer DJ. Social zeitgebers and biological rhythms. A unified approach to understanding the etiology of depression. Archives of General Psychiatry. 1988;45:948–952. doi: 10.1001/archpsyc.1988.01800340076012. [DOI] [PubMed] [Google Scholar]
  8. Elmore SK, Betrus PA, Burr R. Light, social zeitgebers, and the sleep-wake cycle in the entrainment of human circadian rhythms. Research in Nursing and Health. 1994;17:471–478. doi: 10.1002/nur.4770170610. [DOI] [PubMed] [Google Scholar]
  9. Genhart MJ, Kelly KA, Coursey RD, Datiles M, Rosenthal NE. Effects of bright light on mood in normal elderly women. Psychiatry Research. 1993;47:87–97. doi: 10.1016/0165-1781(93)90058-o. [DOI] [PubMed] [Google Scholar]
  10. Golden RN, Gaynes BN, Ekstrom RD, Hamer RM, Jacobsen FM, Suppes T, Wisner KL, Nemeroff CB. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. American Journal of Psychiatry. 2005;162:656–662. doi: 10.1176/appi.ajp.162.4.656. [DOI] [PubMed] [Google Scholar]
  11. Jang KL, Lam RW, Livesly WJ, Vernon PA. The relationship between seasonal mood change and personality: more apparent than real? Acta Psychiatrica Scandinavica. 1997;95:539–543. doi: 10.1111/j.1600-0447.1997.tb10143.x. [DOI] [PubMed] [Google Scholar]
  12. Jean-Louis G, Kripke DF, Assmus JD, Langer RD. Sleep-wake patterns among postmenopausal women: a 24-h unattended polysomnographic study. Journals of Ger-ontology. Series A, Biological Sciences and Medical Sciences. 2000;55:M120–M123. doi: 10.1093/gerona/55.3.m120. [DOI] [PubMed] [Google Scholar]
  13. Jean-Louis G, Kripke DF, Cole RJ, Assmus JD, Langer RD. Sleep detection with an accelerometer actigraph: comparisons with polysomnography. Physiology and Behavior. 2001a;72:21–28. doi: 10.1016/s0031-9384(00)00355-3. [DOI] [PubMed] [Google Scholar]
  14. Jean-Louis G, Kripke DF, Mason WJ, Elliott JA, Youngstedt SD. Sleep estimation from wrist movement quantified by different actigraphic modalities. Journal of Neuroscience Methods. 2001b;105:185–191. doi: 10.1016/s0165-0270(00)00364-2. [DOI] [PubMed] [Google Scholar]
  15. Kasper S, Rogers SLB, Madden PA, Joseph-Vanderpool JR, Rosenthal NE. The effects of phototherapy in the general population. Journal of Affective Disorders. 1990;18:211–219. doi: 10.1016/0165-0327(90)90038-a. [DOI] [PubMed] [Google Scholar]
  16. Kohsaka M, Fukuda N, Honma H, Kobayashi R, Sakakibara S, Koyama E, Nakano T, Matsubara H. Effects of moderately bright light on subjective evaluations in healthy elderly women. Psychiatry and Clinical Neurosciences. 1999;53:239–241. doi: 10.1046/j.1440-1819.1999.00539.x. [DOI] [PubMed] [Google Scholar]
  17. Kripke DF. Light treatment for nonseasonal depression: speed, efficacy, and combined treatment. Journal of Affective Disorders. 1998;49:109–117. doi: 10.1016/s0165-0327(98)00005-6. [DOI] [PubMed] [Google Scholar]
  18. Kripke DF, Drennan MD, Elliott JA. The complex circadian pacemaker in affective disorders. In: Touitou Y, Leung A, editors. Biologic Rhythms in Clinical and Laboratory Medicine. Springer-Verlag; New York: 1992. pp. 265–276. [Google Scholar]
  19. Lam RW, Levitt AJ. Canadian Consensus Guidelines for the Treatment of Seasonal Affective Disorder. Clinical and Academic Publishing; Vancouver, Canada: 1999. [Google Scholar]
  20. Langer RD, White E, Lewis CE, Kotchen JM, Hendrix SL, Trevisan M. The women's health initiative observational study: baseline characteristics of participants and reliability of baseline measures. Annals of Epidemiology. 2003;13:S107–S121. doi: 10.1016/s1047-2797(03)00047-4. [DOI] [PubMed] [Google Scholar]
  21. Lewy AJ, Bauer VK, Cutler NL, Sack RL, Ahmed S, Thomas KH, Blood ML, Jackson JML. Morning vs evening light treatment of patients with winter depression. Archives of General Psychiatry. 1998;55:890–896. doi: 10.1001/archpsyc.55.10.890. [DOI] [PubMed] [Google Scholar]
  22. Lewy AJ, Wehr TA, Goodwin FK, Newsome DA, Markey SP. Light suppresses melatonin secretion in humans. Science. 1980;210:1267–1269. doi: 10.1126/science.7434030. [DOI] [PubMed] [Google Scholar]
  23. Matthews KA, Shumaker SA, Bowen DJ, Langer RD, Hunt JR, Kaplan RM, Klesges RC, Ritenbaugh C. Women's Health Initiative: why now? what is it? what's new? American Psychologist. 1997;52:101–116. doi: 10.1037//0003-066x.52.2.101. [DOI] [PubMed] [Google Scholar]
  24. Michalak E, Tam E, Manjunath C, Levitt A, Levitan R, Lam R. Quality of life in patients with seasonal affective disorder: summer versus winter scores. Canadian Journal of Psychiatry. 2005;50:292–295. doi: 10.1177/070674370505000510. [DOI] [PubMed] [Google Scholar]
  25. Michalak E, Tam E, Manjunath C, Solomons K, Levitt A, Levitan R, Enns M, Morehouse R, Yatham L, Lam R. Generic and health-related quality of life in patients with seasonal and nonseasonal depression. Psychiatry Research. 2004a;128:245–251. doi: 10.1016/j.psychres.2004.01.012. [DOI] [PubMed] [Google Scholar]
  26. Michalak E, Tam E, Manjuth C, Yatham L, Levitt A, Levitan R, Lam R. Hard times and good friends: negative life events and social support in patients with seasonal and nonseasonal depression. Canadian Journal of Psychiatry. 2004b;49:408–411. doi: 10.1177/070674370404900613. [DOI] [PubMed] [Google Scholar]
  27. Molin J, Mellerup E, Bolwig T, Scheike T, Dam H. The influence of climate on development of winter depression. Journal of Affective Disorders. 1996;37:151–155. doi: 10.1016/0165-0327(95)00090-9. [DOI] [PubMed] [Google Scholar]
  28. Monk TH, Flaherty JF, Frank E, Hoskinson K, Kupfer DJ. The Social Rhythm Metric. An instrument to quantify the daily rhythms of life. Journal of Nervous and Mental Disease. 1990;178:120–126. doi: 10.1097/00005053-199002000-00007. [DOI] [PubMed] [Google Scholar]
  29. Murray GW, Hay DA, Armstrong SM. Personality factors in seasonal affective disorder: is seasonality an aspect of neuroticism? Personality and Individual Differences. 1995;19:613–617. [Google Scholar]
  30. Partonen T, Lonnqvist J. Moclobemide and fluoxetine in treatment of seasonal affective disorder. Journal of Affective Disorders. 1996;41:93–99. doi: 10.1016/s0165-0327(96)00073-0. [DOI] [PubMed] [Google Scholar]
  31. Partonen T, Lonnqvist J. Bright light improves vitality and alleviates distress in healthy people. Journal of Affective Disorders. 2000;57:55–61. doi: 10.1016/s0165-0327(99)00063-4. [DOI] [PubMed] [Google Scholar]
  32. Reid S, Towell AD, Golding JF. Seasonality, social zeitgebers and mood variability in entrainment of mood: implications for seasonal affective disorder. Journal of Affective Disorders. 2000;59:47–54. doi: 10.1016/s0165-0327(99)00122-6. [DOI] [PubMed] [Google Scholar]
  33. Rosenthal NE, Genhart M, Sack DA, Skwerer RG, Wehr TA. Seasonal affective disorder and its relevance for the understanding and treatment of bulimia. In: Hudson JI, Pope HG, editors. The Psychobiology of Bulimia. American Psychiatric Press; Washington, DC.: 1987. [Google Scholar]
  34. Tam EM, Lam RW, Levitt AJ. Treatment of seasonal affective disorder: a review. Canadian Journal of Psychiatry. 1995;40:457–466. doi: 10.1177/070674379504000806. [DOI] [PubMed] [Google Scholar]
  35. Terman M, Terman JS, Ross DC. A controlled trial of timed bright light and negative air ionization for treatment of winter depression. Archives of General Psychiatry. 1998;55:875–882. doi: 10.1001/archpsyc.55.10.875. [DOI] [PubMed] [Google Scholar]
  36. Tuunainen A, Langer RD, Klauber MR, Kripke DF. Short version of the CES-D (Burnam screen) for depression in reference to the structured psychiatric interview. Psychiatry Research. 2001;103:261–270. doi: 10.1016/s0165-1781(01)00278-5. [DOI] [PubMed] [Google Scholar]
  37. Wallace-Guy GM, Kripke DF, Jean-Louis G, Langer RD, Elliott JA, Tuunainen A. Evening light exposure: implications for sleep and depression. Journal of the American Geriatrics Society. 2002;50:738–739. doi: 10.1046/j.1532-5415.2002.50171.x. [DOI] [PubMed] [Google Scholar]
  38. WHI Study Group Design of the Women's Health Initiative Clinical Trial and Observational Study. Controlled Clinical Trials. 1998;19:61–109. doi: 10.1016/s0197-2456(97)00078-0. [DOI] [PubMed] [Google Scholar]
  39. Wirz-Justice A, Graw P, Krauchi K, Sarrafzadeh A, English J, Arendt J, Sand L. ‘Natural’ light treatment of seasonal affective disorder. Journal of Affective Disorders. 1996;37:109–120. doi: 10.1016/0165-0327(95)00081-x. [DOI] [PubMed] [Google Scholar]
  40. Youngstedt S, Leung A, Kripke D, Langer R. Association of morning illumination and covering with mood and sleep among post-menopausal women. Sleep and Biological Rhythms. 2004;2:174–183. doi: 10.1111/j.1479-8425.2004.00139.x. [DOI] [PMC free article] [PubMed] [Google Scholar]

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