Time trends in lifetime incidence rates of first‐time diagnosed anorexia nervosa and bulimia nervosa across 16 years in a danish nationwide psychiatric registry study

OBJECTIVE: To study recent time trends in the incidence of diagnosed anorexia nervosa (AN) and bulimia nervosa (BN) based on nationwide psychiatric register data. METHOD: The Danish Psychiatric Central Research Registry was used to identify the incidence of diagnosed cases with AN and BN at the ages of 4-65 years from 1995 to 2010. Age- and sex-adjusted incidence rates per 100,000 person-years were calculated and were adjusted for time trends in the total number of people diagnosed in psychiatry. Time trends were analyzed using JoinPoint regression analysis. RESULTS: A total of N = 5,902 persons had a first-time incidence of AN, and a total of N = 5,113 had first-time incidence of BN. Incidence rates increased for AN from 6.4 to 12.6 per 100,000 person-years, and for BN from 6.3 to 7.2 per 100,000 person-years. In 2010, the male-to-female ratio was 1:8 for AN, and 1:20 for BN. There was an earlier onset for AN than for BN, and age at incidence decreased during the observation period for AN but not for BN. A sizeable part of the increasing incidence rates for AN and in particular, the younger AN age groups, could be attributed to an increase in the total number of N = 249,607 persons with first-time diagnoses in psychiatry. DISCUSSION: Incidence rates had increased slightly for AN, but were stable for BN across 16 years in this nationwide study and to a large extent were reflective of a general increase in diagnosed mental disorders.