3. Prevalence of GAD in population samples and in primary
care
European and U.S. prevalence studies show similar rates of GAD in
the adult population. For example, a representative sample of
10,000 twins in Sweden aged 55e74 years was interviewed about
GAD symptomatology.12 The lifetime risk of GAD was estimated at
3.95% in women and 1.74% in men. The genetic contribution was
27% and individual environmental factors 72%. Thus, only 1% was
accounted for by shared environment, such as parenting.
A British population study found that 3% of those interviewed
had GAD, and only 8% of those diagnosed with GAD were in
treatment with medications or psychotherapy.13 A populationbased
survey of GAD in Hong Kong found a 3.4e4.0% 12-month
prevalence.14
Turning to GAD in health care settings, the chances of identifying
the disorder are influenced by comorbidity. Secondary
depressions are common in GAD, as shown in prospective and
longitudinal studies.15 This is usually the time when a GAD patient
first seeks help, after several years of trying to cope with worry.
General practitioners more easily recognize GAD patients who
appear with secondary depression and are more likely to institute
treatment.16
On a typical working day in 2001, 648 general practitioners in
Sweden and their 8879 patients participated in a comprehensive
survey to identify cases of GAD in primary care.17 The agestandardized
rate of GAD was 4.1e6.0% among men and 3.7e7.1%
among women.
Ethnic aspects influence the symptomatology of anxiety disorders,
with a shift toward somatizing in Asians, called distress
syndromes.18,19 GAD, panic disorder, and posttraumatic stress
disorder may have other names in Asian cultures stemming from
traditional medicine in China, Cambodia, Vietnam, and Thailandd
for example, shenjing shuairuo, wind overload, weak heart and
weak kidney, and neck soreness. Hwa byung is marked by catastrophic
cognition about negative emotions in Korea. Neurasthenia
is another term used in Japan and China that probably overlaps with
GAD. Illness attribution and illness presentations need to be
considered in treating patients in their ethnic environment or in
migration to western society. The pharmacodynamics and pharmacokinetics
of medications for GAD, usually assessed in western
populations, may also be influenced by pharmacogenetic factors