BOSTON -- The death rate in Massachusetts dropped significantly after it adopted mandatory health care coverage in 2006, a study released Monday found, offering evidence that the nation's first experiment with universal coverage -- and the model for crucial parts of President Barack Obama's health care law -- has saved lives, health economists say.
The study tallied deaths in Massachusetts from 2001 to 2010 and found that the mortality rate -- the number of deaths per 100,000 people -- fell by about 3 percent in the four years after the law went into effect. The decline was steepest in counties with the highest proportions of poor and uninsured people. In contrast, the mortality rate in a control group of counties similar to Massachusetts in other states was largely unchanged.
A national 3 percent decline in mortality among adults under 65 would mean about 17,000 fewer deaths a year.
"It's big," said University of Pennsylvania demographer Samuel Preston, an authority on life expectancy. Mr. Preston, who was not involved in the study, called the research "careful and thoughtful," and said it added to a growing body of evidence that people with health insurance could reap the ultimate benefit -- longer life.
Experts said the study, published online Monday in the Annals of Internal Medicine, will not settle the long-debated question of whether being insured prolongs life, but it provides the most credible evidence yet that it might. Still, health improvements can take years to surface in mortality data, and some researchers were skeptical of the magnitude and suddenness of the decline.
"Health care is a much more involved process -- you don't just sign up and suddenly get well," said Joseph Antos, a health economist at the conservative American Enterprise Institute.
Massachusetts is whiter and more affluent than most states, and has more doctors per capita and fewer uninsured people. But researchers said the state's health insurance law nevertheless amounted to the best natural experiment the nation has had for testing effects of a major insurance expansion on a large population. Another study, in Oregon, found that Medicaid, the insurance program for the poor, improved mental health and financial security, but not physical health, and the study was too small to gauge mortality effects.
"This is an important piece of the puzzle," Katherine Baicker, a professor of health economics at the Harvard School of Public Health, who took part in both studies, said of the Massachusetts one. "Putting the evidence together paints a very strong picture that expanding insurance substantially improves the well-being of people who get it."
In the waiting rooms of the East Boston Neighborhood Health Center, bustling with a working-class clientele, doctors said much had changed since the state insurance law passed in 2006. People are less likely to put off care out of fear of unaffordable bills, and patients with diabetes can get medication regularly.
Stelios Maheras, medical director of the emergency department, said some patients used to ask for prices "like at the supermarket." Dr. Maheras recalled one patient who was having chest pains but refused an ambulance because he was afraid of the bill.
In Suffolk County, which includes Boston, the death rate for adults under 65 dropped about 7 percent from 2005 to 2010, the study's authors said.
The authors identified 513 counties in 46 other states that were most similar to Massachusetts before reform in demographics and levels of poverty and insurance, then compared their mortality rates to that of Massachusetts. They found that the rate declined 2.9 percent in Massachusetts, but remained flat in counties outside the state.
Researchers also examined death rates for people 65 and over, a population minimally affected by the insurance overhaul. Mortality patterns over time in that age group were the same in Massachusetts and the control counties.
Lead author Benjamin Sommers, a health economist and a Harvard School of Public Health physician, cautioned that researchers did not have individual data on the 270,000 people who had gained insurance in the state, and could not tell for sure whether it was the expansion that had driven the mortality decline.
Researchers have long debated whether health insurance and better access to medical care saves lives, but it has been hard to construct a study to settle the issue. In 2002, the Institute of Medicine estimated that a lack of health insurance was responsible for 18,000 deaths a year in the United States. But in 2009, a University of California researcher found that the survival rate of uninsured people resembled that of insured people.
There will be more evidence in coming years. The Affordable Care Act is its own sweeping experiment, because only about half the states expanded Medicaid. "It's very unfortunate for people living in states not expanding Medicaid," said Richard Kronick, a health policy official at the Department of Health and Human Services, "but from the point of view of research, it's a gold mine."