Why is this review important?
Many people in northern latitudes suffer from winter blues, which occurs as a reaction to reduced sunlight. Three-quarters of those affected are women. Lethargy, overeating, craving for carbohydrates and depressed mood are common symptoms. In some people, winter blues becomes depression, which seriously affects their daily lives. Up to two-thirds experience depressive symptoms every winter.
Who will be interested in this review?
Anyone who has experienced winter depression, or who has relatives and friends who have experienced winter depression.
What questions does this review aim to answer?
In light of the seasonal pattern and the high rate of recurrence, beginning light therapy in early autumn (fall) when people are still free of depressive symptoms could help to prevent the onset of depressed mood. The goal of this review was to find out whether light therapy can prevent the onset of depression in winter when it is used in healthy people with a history of winter depression, and if it is safe. To date, this question has not been examined in a systematic way, but it is of importance for those who have suffered winter depression.
Which studies were included in the review?
We searched databases up to 19 June 2018 for studies on light therapy to prevent winter depression. Among 3745 records, we found one randomised controlled study including 46 people who received light therapy or no treatment. All individuals in these studies had a history of winter depression.
What does the evidence from the review reveal?
The quality of evidence for all outcomes was very low, so we can draw no conclusions about whether light therapy is effective in preventing winter depression. The included study provided no information on side effects of light therapy.
Doctors need to discuss with patients considering preventive treatment the advantages and disadvantages of light therapy and other potentially preventive treatments for winter depression, such as drug treatments, psychological therapies or lifestyle interventions. As no available studies have compared these treatments, treatment selection should be strongly based on patient preferences.
What should happen next?
The review authors recommend that future studies should directly compare light therapy versus other treatments, such as drug treatments, psychological therapies or lifestyle interventions to determine the best treatment for preventing winter depression.
Evidence on light therapy as preventive treatment for people with a history of SAD is limited. Methodological limitations and the small sample size of the only available study have precluded review author conclusions on effects of light therapy for SAD. Given that comparative evidence for light therapy versus other preventive options is limited, the decision for or against initiating preventive treatment of SAD and the treatment selected should be strongly based on patient preferences.
Seasonal affective disorder (SAD) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring. The prevalence of SAD ranges from 1.5% to 9%, depending on latitude. The predictable seasonal aspect of SAD provides a promising opportunity for prevention. This review - one of four reviews on efficacy and safety of interventions to prevent SAD - focuses on light therapy as a preventive intervention. Light therapy is a non-pharmacological treatment that exposes people to artificial light. Mode of delivery and form of light vary.
To assess the efficacy and safety of light therapy (in comparison with no treatment, other types of light therapy, second-generation antidepressants, melatonin, agomelatine, psychological therapies, lifestyle interventions and negative ion generators) in preventing SAD and improving patient-centred outcomes among adults with a history of SAD.
We searched Ovid MEDLINE (1950- ), Embase (1974- ), PsycINFO (1967- ) and the Cochrane Central Register of Controlled Trials (CENTRAL) to 19 June 2018. An earlier search of these databases was conducted via the Cochrane Common Mental Disorders Controlled Trial Register (CCMD-CTR) (all years to 11 August 2015). Furthermore, we searched the Cumulative Index to Nursing and Allied Health Literature, Web of Science, the Cochrane Library, the Allied and Complementary Medicine Database and international trial registers (to 19 June 2018). We also conducted a grey literature search and handsearched the reference lists of included studies and pertinent review articles.
For efficacy, we included randomised controlled trials (RCTs) on adults with a history of winter-type SAD who were free of symptoms at the beginning of the study. For adverse events, we also intended to include non-randomised studies. We intended to include studies that compared any type of light therapy (e.g. bright white light, administered by visors or light boxes, infrared light, dawn stimulation) versus no treatment/placebo, second-generation antidepressants, psychological therapies, melatonin, agomelatine, lifestyle changes, negative ion generators or another of the aforementioned light therapies. We also planned to include studies that looked at light therapy in combination with any comparator intervention.
Two review authors screened abstracts and full-text publications, independently abstracted data and assessed risk of bias of included studies.
We identified 3745 citations after de-duplication of search results. We excluded 3619 records during title and abstract review. We assessed 126 full-text papers for inclusion in the review, but only one study providing data from 46 people met our eligibility criteria. The included RCT had methodological limitations. We rated it as having high risk of performance and detection bias because of lack of blinding, and as having high risk of attrition bias because study authors did not report reasons for dropouts and did not integrate data from dropouts into the analysis.
The included RCT compared preventive use of bright white light (2500 lux via visors), infrared light (0.18 lux via visors) and no light treatment. Overall, white light and infrared light therapy reduced the incidence of SAD numerically compared with no light therapy. In all, 43% (6/14) of participants in the bright light group developed SAD, as well as 33% (5/15) in the infrared light group and 67% (6/9) in the non-treatment group. Bright light therapy reduced the risk of SAD incidence by 36%; however, the 95% confidence interval (CI) was very broad and included both possible effect sizes in favour of bright light therapy and those in favour of no light therapy (risk ratio (RR) 0.64, 95% CI 0.30 to 1.38; 23 participants, very low-quality evidence). Infrared light reduced the risk of SAD by 50% compared with no light therapy, but the CI was also too broad to allow precise estimations of effect size (RR 0.50, 95% CI 0.21 to 1.17; 24 participants, very low-quality evidence). Comparison of both forms of preventive light therapy versus each other yielded similar rates of incidence of depressive episodes in both groups (RR 1.29, 95% CI 0.50 to 3.28; 29 participants, very low-quality evidence). Reasons for downgrading evidence quality included high risk of bias of the included study, imprecision and other limitations, such as self-rating of outcomes, lack of checking of compliance throughout the study duration and insufficient reporting of participant characteristics.
Investigators provided no information on adverse events. We could find no studies that compared light therapy versus other interventions of interest such as second-generation antidepressants, psychological therapies, melatonin or agomelatine.