Seasonal variation in anorexia nervosa? Some preliminary findings from a neglected area of research

Abstract

A review of the literature on normal development and on psychiatric disorders related to seasonal variation, suggests that this phenomenon is probable to occur in anorexia nervosa. A search of the available literature is entirely negative with respect to seasonal variation in anorexia nervosa. Preliminary analysis suggests the existence of a season of onset, a season of birth, and also oi a season of admission in Danish female anorexia nervosa patients. A formally correct analysis for seasonal variation supports the existence of a season of onset in a selected sample, maximum is in May, amplitude 50%. A season of birth is found in an unselected nationwide sample of patients aged 15 years or older at first psychiatric admission for anorexia nervosa. Maximum late in April, amplitude 40% in the period 1963–1968. Season of admission could not be modelled as a sine wave, but the data suggested a pulse structure (a minimum in one month, followed by a maximum in the next month). Two annual pulses: December/January and July/August. Peak of onset is at a time of the year with maximum increase in height, and peak of other psychiatric conditions. Pattern of birth is similar to that reported for schizophrenia and mania. Replications of this preliminary study should be done in larger countries, at different latitudes and continents. Geophysical, demographic, and climatological variables should be controlled.

Is season of birth related to disordered eating and personality in women with eating disorders?

“…By ignoring missing birth date data, most studies [e.g., (1, 2, 8)] did not account for exactness of birth dates. We excluded participants missing these data while employing a sample large enough to make meaningful comparisons.…”

“…In some studies, eating disorder samples were compared to the general population (1, 5, 6). Often control participants’ birth years only partly overlapped with affected participants’ (3, 5, 6).…”

“…As birth rates differ across time, control and eating disorders groups should assess the same birth years. Differing diagnostic systems and sample selection (1, 3, 5) have made comparative interpretations difficult. We clearly defined diagnostic criteria and used experienced assessors.…”

“…Occasional studies report that eating disorders occur more frequently in those born from February to June (1–6). One noted stronger restrictive eating attitudes in a non-clinical population in those born between May and August (7).…”

Season of birth and disordered eating in a population‐based sample of young U.S. females

“…Finally, because the aforementioned spring SoB bias for AN is thought to be greater for early-onset AN13, we identified from among the underweight and dieting/weight concern group those females who reported those symptoms in any survey year prior to 15 years of age, who then comprised the early-underweight and dieting/weight concern subgroup. (We used a cutoff of age 15 to be consistent with the original study1 of season of birth and AN. )…”