Abstract:
The “winter blues” would appear to be a global concept. This thesis examined features of
depression, seasonal change and meteorological data in relation to theories on the
development of seasonal depression and Seasonal Affective Disorder (SAD). It reviewed
the neurotransmitter based theories of causation where increased exposure to light is
thought to stimulate normal neurotransmitter production. It also examined the dual
vulnerability hypothesis (DVH) which postulated that vegetative symptoms arose from a
different vulnerability than depressive symptoms. Levels of vegetative symptoms and
depression were analysed in relation to the different climate experienced in Auckland,
New Zealand. Three studies were undertaken. In the first study, the sample consisted of
195 individuals in New Zealand who self-referred to participate in a separate research
project examining the effects of “homework” and cognitive behavioural therapy for first
time depression. Meteorological data were investigated in order to explore any potential
vulnerability to seasonal depression in this sample. Additionally, age and gender were
explored in relation to season of presentation. The second study involved the subsample
(n = 81) who were assessed for therapy and examined season and symptom profile in
relation to when the person presented. The third study traced the progress through
therapy of 28 adults who were selected from the second study for CBT. The Beck
Depression Inventory (BDI-II) provided additional data to test the related hypotheses
Rate of change in depression scores and symptom expression in relation to seasonality
were analysed using multilevel modelling (MLM). Daily hours of bright sunlight was
found to have an unusual relationship to temperature in New Zealand when compared
with previous research. In this setting increased sunshine was associated with lower
temperatures. Therefore, the variables were separated in order to ascertain whether one
affected results more than others. Bright sunshine hours affected the expression of
vegetative symptoms with a decrease observed over time in relation to increased
photoperiod. Subtle relationships between temperature and vegetative symptoms were
observed. However, there was an overall lack of correlation between vegetative and
depressive symptoms observed in the CBT sample, and sunlight was not observed to
have any effect on typical depressive symptoms. The investigation provided partial
support for the neurotransmitter basis of vegetative symptoms and for the dual
vulnerability hypothesis. Gender and age were correlated with vegetative symptom
endorsement, although over time only gender was found to have any ongoing
significance in the presentation of seasonal symptoms with women more likely to exhibit
vegetative responses over time.
