People with health insurance are more likely to have their high cholesterol, diabetes, and high blood pressure correctly diagnosed--and to have these chronic conditions under control--than similar uninsured people, according to a new study led by researchers at Harvard T.H. Chan School of Public Health.

Using these results and 10-year Affordable Care Act (ACA) enrollment projections from the Congressional Budget Office (CBO), the researchers developed an estimate of the number of Americans who might benefit from improved diagnosis and treatment of chronic disease through the expansion of health insurance coverage. They estimated that if the number of nonelderly Americans without health insurance were reduced by half, as the CBO projects, there would be 1.5 million newly insured individuals diagnosed with one or more of these conditions, and 659,000 newly insured individuals able to achieve control of at least one condition.

"These effects constitute a major positive outcome from the ACA," said senior author Joshua Salomon, professor of global health. "Our study suggests that insurance expansion is likely to have a large and meaningful effect on diagnosis and management of some of the most important chronic illnesses affecting the U.S. population."

The study appears in the September 2015 issue of Health Affairs.

The researchers analyzed data from 28,157 people ages 20-64 participating in the National Center for Health Statistics' National Health and Nutrition Examination Survey (NHANES) from 1999-2012. The researchers found that insured people had a significantly higher probability of being diagnosed with a chronic disease than similar people without insurance--by 14 percentage points for diabetes and high cholesterol, and 9 percentage points for high blood pressure. Among those already diagnosed, having insurance was associated with higher probabilities of achieving standard clinical benchmarks for control of each condition, and with significantly healthier average levels of blood sugar, total cholesterol, and systolic blood pressure.

While these effects represent a step toward achieving the ACA's objective of improving health, "they also remind us that there is urgent need to ensure that the U.S. health care system is equipped to provide high quality care for large numbers of people who will be newly diagnosed with a chronic disease," said Salomon.