A study conducted jointly by Cornell, Indiana and Carnegie Mellon Universities, estimates that 9.3 million people lost health insurance between 2007 and 2009.

"The Great Recession of 2007-09 is the longest and deepest macroeconomic downturn in the United States since 1933," they write. "This paper documents the impact of higher unemployment rates on one important outcome: health insurance coverage."

The 9.3 million figure is the difference in the number of adults with insurance coverage at the macroeconomic peak in December 2007 compared to the trough of June 2009. The study also shows in increase in the number of children (under age 18) insured in the same time, which proves that the social safety net works counter-cyclically.  As parents lose jobs and coverage, more children qualify for Medicaid and various state medical plans. 
Of the adults who lost coverage, men made up 7.1 million and women 2.2 million.

Just days after writing the above, (on December 14, 2011) the Department of Health and Human Services announced that since the inception of the health care reform bill (Sept. 23, 2010), an additional 2.5 million adults aged 19-25 had gained health insurance.  It was reported that 72.7% of adults that age were now insured compared to 64.4% in 2010.  The increase is attributed to a provision in the bill that requires employers to extend coverage to their employees’ children up to age 26.