Secular trends in the incidence of anorexia nervosa: integrative review of population-based studies.

OBJECTIVE AND
METHOD: Aggregating across retrospective cohort samples, this integrative review synthesizes the findings of 12 cumulative incidence studies (45 hypotheses) on anorexia nervosa secular trends.
RESULTS: (1) The female/male anorexia incidence rate ratio was estimated to be 8.20, 18.46 versus 2.25 cases per 100,000 per year, p < .05; (2) female teenagers experienced anorexia at a rate fivefold greater than other women, 50.82 versus 10.37 incident cases per 100,000 per year, p < .001; (3) no secular trend or change in the incidence of anorexia was observed among teenagers, while a near threefold increase was observed over the past 40 years among women in their 20s and 30s, 6.28 (1950-1964) versus 17.70 (1980-1992) cases per 100,000 per year, p < .05; and (4) the two cohort characteristics of age, and the age by year interaction accounted for nearly two thirds of the variability among anorexia incidence estimates, R2 = .614, F(2,27) = 21.49, p < .001. After the two factors of age and the Age x Year interaction were accounted for, none of the other study characteristics, including study year(s), were found to be significantly associated with anorexia incidence, that is, a main effect of time was not observed. DISCUSSION: The integrative evidence across the population-based epidemiologic studies covering 40 years in this field suggests strongly that, overall, the incidence of anorexia nervosa, particularly among those very young women at greatest risk of experiencing it, has not increased significantly. However, the risk does seem to have increased significantly among women in their 20s and 30s.