The overarching question of whether nondrug interventions such as phototherapy and vitamin therapy might lead to better outcomes in SAD can be answered only in part because studies were found on phototherapy, but not on vitamin D therapy. Below, the domain-specific results are presented and synthesized.

For phototherapy with patient-facing light boxes, indications of benefit were derived. Patients using such light boxes responded more frequently to therapy, were more successful in achieving remission of depression, and reported less severe symptoms of depression at the end of the intervention than patients receiving sham treatment. However, it must be noted that the studies suffered from a high risk of bias as well as a risk of random errors due to small study sizes. In addition, slightly less than half of users neither showed any response nor achieved remission despite phototherapy. For phototherapy with HMUs, no hint of benefit was derived, and for dawn simulation, a hint of benefit was derived only for the outcome of response [45–47,49–51,53,56–58,60,67,68,70–73].

In direct comparison with other treatment options, no hint can be derived of light box therapy having any greater benefit than the antidepressant fluoxetine or cognitive behavioural therapy [54,55,59,60,62,66]. Response or remission rates for all 3 interventions were around 50%, but the confidence intervals were broad. Overall, AEs such as headache or eye pain were reported only in isolated cases. There is no hint of phototherapy being more likely to lead to AEs than placebo [46,47,57,67,71,73]. Since the studies surveyed AEs only until the end of the intervention, it is not possible to assess any long-term harm of phototherapy, e.g. permanent eye damage. However, there is a hint of certain AEs being more commonly caused by fluoxetine treatment than by phototherapy [54,55]. Light box therapy is therefore likely associated with a short-term benefit regarding depression-related outcomes and with few short-term AEs. However, the long-term effects of light box therapy are unknown.

No studies were found on the outcome of mortality. Since only 1 study each reported the outcomes of functioning and health-related quality of life, no meaningful conclusions about the benefit of the interventions can be drawn with regard to these outcomes.

The health economic systematic review found 2 health economic studies, but they failed to meet the central methodological standards. Due to the U.S. setting and a lack of relevant comparators, these studies were of very limited informative value and their conclusions are not transferable to the German healthcare system. However, it was possible to calculate intervention costs for the German healthcare context.

Phototherapy can be administered either at home or on an outpatient basis at a hospital or medical practice. When administered at a practice or hospital, a set of 28 sessions at 40 minutes each costs patients between EUR210 and 390.32. Phototherapy is typically an out-of-pocket service and is reimbursed by few SHIs. In case of therapy at home with the patient’s own device, costs primarily include the device’s purchase price, ranging from EUR59.99 to EUR430. The initial and final consultations cost about EUR102 extra. However, some SHIs offer a (partial) reimbursement in this case as well. Vitamin D therapy is not reimbursable for the indication of SAD [80]. The intervention costs for 8 weeks of vitamin D therapy include 50 vitamin D soft capsules at a dose of 20 000 IU each as well as an additional ligand-binding assay plus the costs of psychiatric care, for a total of approximately EUR182. In terms of the intervention costs of the comparator therapies, the focus was on SSRI treatment with fluoxetine as well as cognitive behavioural therapy since, in the benefit assessment, studies were found only on these two interventions. For fluoxetine therapy (acute treatment and follow-up), the reimbursable costs ranged from EUR184.91 to 185.10. The total cost of cognitive behavioural therapy is EUR1115.23 in a group of 4, EUR834.67 in a group of 8, and EUR1359.92 in individual therapy. This cost can be billed to the SHI.

The focus on biological causes might lead to SAD being less stigmatized in society than nonseasonal depression. However, societal doubts as to whether SAD is actually a clinical picture or a “normal” part of winter represent ethical and social challenges [103]. Patients report perceiving physicians as lacking awareness of SAD, which might lead to delayed or missed diagnosis and late or no treatment of SAD [104]. Considering the greater vulnerability of many SAD patients, protecting them is particularly important.

Patient acceptance of phototherapy is likely high, particularly because it represents a nondrug alternative and many people have negative attitudes toward drug therapies [9,108]. Given the high sales of vitamin D preparations in Germany, the acceptance of vitamin D in the general population seems equally high [10]. In this context, the ethical and social challenge is the lack of SHI coverage of phototherapy and vitamin D therapy, while the cost of comparator therapies such as fluoxetine or cognitive behavioural therapy are covered. In acute SAD, drug therapy with antidepressants is recommended most frequently [28], despite the fact that the benefit assessment failed to show a hint of greater benefit of antidepressants in comparison with phototherapy in SAD patients.

A particularly relevant issue from a legal perspective is for physicians to inform patients about nondrug SAD treatment options, such as phototherapy. While specialists in the clinical setting often recommend phototherapy to SAD patients [28], patients report that this is not yet the case in the general practice setting. In addition, patients expect to receive more information as well as support and consultation in the selection of light devices [104].

From an organizational perspective, the implementation of phototherapy and vitamin D therapy does not require more personnel because both therapies can be independently implemented by the patient. An increased use of phototherapy in hospitals or practices is not expected to lead to any shifts in services because the same healthcare professionals responsible for these therapies are also responsible for antidepressant therapy. No further forms of communication would be needed, because the treatment methods do not require any coordination with other service providers.