July 26, 2011 -- Depression rates around the world vary according to a nation's affluence, with the highest income countries -- including the U.S. -- reporting the highest levels of depression, a study shows.
For the study, an international team working with the World Health Organization's World Mental Health Survey Initiative interviewed nearly 90,000 people in eighteen countries. The researchers assessed their mental health using criteria for major depressive episode (MDE).
The study is published in BMC Medicine.
The World Health Organization estimates that depression affects 121 million people worldwide. In the 10 higher income countries surveyed, an average of nearly 15% of the population had suffered from depression at least once in their lives. By contrast, people living in low to middle income countries reported an 11% likelihood of having had the disease.
At 19.2%, the U.S. had the second highest lifetime rate of depression. Only France, at 21%, had a greater frequency of the disease. Among the high-income countries, Japan, Germany, Italy, and Israel reported the smallest percentages, ranging from under 7% to 10%.
Low to middle income countries, by contrast, reported much lower rates overall. China (6.5%) and Mexico (8%) had the smallest percentage of lifetime incidence of depression. Only Brazil, at 18.4%, approached the level of depression in the U.S.
The researchers also measured the rates of depression that occurred in the year preceding the survey. Brazil had the highest level overall; an estimated 10% of its population experienced depression in the previous year. The United States, with the second highest rates, reported an 8.3% rate. Japan, Germany, and Italy had the lowest 12-month rates.
People in the U.S. also appear to suffer from depression at an earlier age than people in other high-income countries. The median age for the onset of the disease in the U.S. was 22.7. In New Zealand, the next earliest, the median was 24.2. Spain and Japan had the latest average age of onset at 30 and 30.1, respectively. Out of all countries, both high and low income, China had the youngest depressed population. The age of onset there was 18.8.