• anorexia nervosa;
  • eating disorders;
  • seasons;
  • reproduction;
  • psychotic disorders



A preponderance of births between April and June in patients with anorexia nervosa (AN) and other eating disorders (EDs) has recently been explained by a higher environmental temperature at conception. This hypothesis, however, does not explain some other irregularities in the month of birth distribution in contrast to the seasonal preovulatory overripeness ovopathy (SPrOO) and seasonal optimally ripened oocytes (SOptRO) hypotheses.


The month of birth distribution of 408 patients with EDs from Southeast England and of 199 patients from Australia has been reassessed in relation to previously determined high-risk and low-risk months based on a priori knowledge from mammals and on the physiologic birth peaks and troughs in humans at population level. The differences between high-risk and low-risk months were assessed by conventional chi-square analyses and by relative risks (RRs) with 95% confidence intervals (CI).


In England, fewer AN patients (n = 259) were born at the peaks of the total birth pattern, that is, during the 2 low-risk months, and more were born during the transitional stages, that is, during the remaining 10 high-risk months (p = .004; RR = 1.66 [95% CI = 1.13–2.41]). After the addition of 149 other ED patients (n = 408), this result remained (p = .005; RR = 1.47 [95% CI = 1.10–1.97]). Similar results were found in 199 ED patients from Australia (p = .009; RR =1.70 [95% CI = 1.09–2.64]).


ED patients appear to be more frequently conceived during the transitional stages of the ovulatory pattern due to SPrOO and less frequently at the ovulatory peaks due to SOptRO. The pathophysiologic processes of oocyte maturation in estrous animals and the circumstantial evidence of similar phenomena in humans are more appropriate to explain these coincidences than the temperature at conception hypothesis. © 2005 by Wiley Periodicals, Inc.