A season of birth bias is said to be present if the season of birth pattern for a particular group varies from the pattern within the local normal population. Such a phenomenon may contribute to the aetiological understanding of psychological disorders, perhaps by identifying subgroups within heterogeneous diagnostic categories. This can have implications for treatment. For example, season of birth biases have been identified for subgroups within the eating disorder category, especially for patients with anorexia nervosa (AN).
This dissertation will review the findings from season of birth research in eating disorders and summarize some methodological issues. Two proposed hypothesis that aim to explain this bias, will be explored. As an additional contribution to the field, one of those will be developed further. Directions for future research to expand this field of knowledge will be offered throughout.
Despite methodological issues that need to be addressed, the reviewed papers consistently show a season of birth bias for AN. Here is a brief presentation of the two hypotheses that will be explored:
The first hypothesis claims that the fertility of some thin, food restricting women will vary as a consequence of temperature fluctuation through the year. This is due to a higher need to use energy to maintain bodily temperature in colder months. Conception is more likely in the warmer months, leading to spring births. Encouragement and modelling of restrictive eating will increase the child s vulnerability for AN. The second hypothesis proposes that it is variations in sunlight exposure that lead to the observed bias. This could happen because; i) Intense ultraviolet radiation might cause maternal oxidative stress or mutations, both which may alter the neurodevelopment in some foetuses. This leaves them vulnerable for AN. ii) Higher levels of sunlight exposure might alter the mothers mood by lifting symptoms of depression. This may improve her sexual life, increasing likelihood of conception in the summer. iii) The interaction between the mother-child might be altered as a consequence of a higher birth weight in the spring due to increased sunlight exposure during the first trimester of gestation. The interaction increases the child s vulnerability to AN.
Based on this discussion of the methodological issues, discussion and development of these hypotheses, future research can settle if the SoBB in ED is a fact or fiction.