THURSDAY, March 8 (HealthDay News) -- Black Americans are more likely than whites to suffer severe, untreated and disabling depression, U.S. research shows.

Researchers at the Harvard School of Public Health analyzed data on 6,082 people who took part in a national survey conducted between 2001 and 2003.

They found that 17.9 percent of white Americans had depression at some point in their lives, compared with 10.4 percent of blacks of African descent and 12.9 percent of blacks of West Indian or Caribbean descent.

Rates of depression in the 12 months before they were surveyed were 7.2 percent for Caribbean blacks; 6.9 percent for whites; and 5.9 percent for blacks of African descent. Among those who reported depression at some point in their lives, rates of depression in the 12 months before they were surveyed were 56.5 percent for blacks of African descent; 56 percent for Caribbean blacks; and 38.6 percent for whites.

"Fewer than half of the African Americans (45 percent) and fewer than a quarter (24.3 percent) of the Caribbean blacks who met the criteria (for depression) received any form of major depressive disorder therapy," the study authors wrote.

About 57 percent of white Americans with major depression received treatment.

"In addition, relative to whites, both black groups were more likely to rate their major depressive disorder as severe or very severe and more disabling," the researchers reported in the March issue of the Archives of General Psychiatry.

Investigating why blacks may be less likely to develop depression and why they fare worse when they do develop the condition may help improve understanding about depression.

"Future research should explore the extent to which social support systems, including religious participation and psychological resources, such as high levels of self-esteem, can provide some protection to the black population from exposure to adverse social conditions." the study authors wrote.