I've heard a lot of people claiming they they have a disorder called Seasonal Affected Disorder.
Is there any research that indicates this is an actual mental disorder?
Yes....Scientific research supports seasonal relationships with changes in mood....changes that can cause depressive episodes. As described by the Mayo Clinic .....
Seasonal affective disorder is a cyclic, seasonal condition. This means that signs and symptoms come back and go away at the same time every year. Usually, seasonal affective disorder symptoms appear during late fall or early winter and go away during the sunnier days of spring and summer. Some people have the opposite pattern and become depressed with the onset of spring or summer. In either case, problems may start out mild and become more severe as the season progresses.
I found the following bits on the research helpful for a start (there is a lot of research...these are really small bits).....
The initial focus of the pathophysiology of SAD was on circadian rhythm theories, but research interest has expanded to include hypotheses related to abnormalities in monoamine neurotransmitters, personality and genetics (Lam and Levitan, 2000; Partonen and Magnusson, 2001)....
.....Neurotransmitters and genetics. A robust body of research also supports the role of neurotransmitters such as serotonin in the pathophysiology of SAD (Neumeister et al., 2001a). For example, neuroendocrine studies have shown evidence for serotonergic dysregulation in SAD.
Sorry this is a bit long. I tried cutting it down....and failed.
Past studies in rodents have demonstrated circannual variation in central dopaminergic activity as well as a host of compelling interactions between melatonin--a scotoperiod-responsive neurohormone closely tied to seasonal adaptation--and dopamine in the striatum and in midbrain neuronal populations with striatal projections. In humans, seasonal effects have been described for dopaminergic markers in CSF and postmortem brain, and there exists a range of affective, psychotic, and substance abuse disorders that have been associated with both seasonal symptomatic fluctuations and dopamine neurotransmission abnormalities. Together, these data indirectly suggest a potentially crucial link between circannual biorhythms and central dopamine systems. However, seasonal effects on dopamine function in the living, healthy human brain have never been tested. For this study, 86 healthy adults underwent (18)F-DOPA positron emission tomography (PET) scanning, each at a different time throughout the year. Striatal regions of interest (ROIs) were evaluated for differences in presynaptic dopamine synthesis, measured by the kinetic rate constant, K(i), between fall-winter and spring-summer scans. Analyses comparing ROI average K(i) values showed significantly greater putamen (18)F-DOPA K(i) in the fall-winter relative to the spring-summer group (p = 0.038). Analyses comparing voxelwise K(i) values confirmed this finding and evidenced intrastriatal localization of seasonal effects to the caudal putamen (p < 0.05, false-discovery rate corrected), a region that receives dopaminergic input predominantly from the substantia nigra. These data are the first to directly demonstrate a seasonal effect on striatal presynaptic dopamine synthesis and merit future research aimed at elucidating underlying mechanisms and implications for neuropsychiatric disease and new treatment approaches.
Light therapy can be an effective treatment for mood disorders, suggesting that light is able to affect mood state in the long term. As a first step to understand this effect, we hypothesized that light might also acutely influence emotion and tested whether short exposures to light modulate emotional brain responses. During functional magnetic resonance imaging, 17 healthy volunteers listened to emotional and neutral vocal stimuli while being exposed to alternating 40-s periods of blue or green ambient light. Blue (relative to green) light increased responses to emotional stimuli in the voice area of the temporal cortex and in the hippocampus. During emotional processing, the functional connectivity between the voice area, the amygdala, and the hypothalamus was selectively enhanced in the context of blue illumination, which shows that responses to emotional stimulation in the hypothalamus and amygdala are influenced by both the decoding of vocal information in the voice area and the spectral quality of ambient light. These results demonstrate the acute influence of light and its spectral quality on emotional brain processing and identify a unique network merging affective and ambient light information.