A shocking study, published in the journal JAMA Internal Medicine, suggested that health insurance could be good for your health.

Harvard researchers surveyed the well being of roughly 9,000 low-income people in Arkansas, Kentucky, and Texas from 2013 to last year. In the time course, Arkansas and Kentucky increased Medicaid healthcare as part of the Affordable Care Act, and Texas didn’t.

During the study course, survey respondents in Arkansas and Kentucky not just reported enhancements in their quality and access care, but had 5% more chances of saying they possessed excellent health in comparison to Texas counterparts.

The results aren’t perhaps surprising, but they have come up with some first hard data that the ACA has really been enhancing the health of the 20 million people in America who gained insurance as part of the elaborate health law.

However, the authors have warned that it’s only a correlation. The data hasn’t clearly proved the role of ACA in any recorded health improvements. Harvard researchers mentioned that the study design ‘precludes any clear causal interpretation’.

Even then the data collected in the three years- from 2013, prior to the law’s Medicaid extension came into existence, to the end of 2014 and again in last year- recorded stepwise improvements, with most of the gains noted in 2015.

By last year, Arkansas and Kentucky survey participants were 22.7% less likely in comparison to Texans to say that they had no insurance. Arkansans and Kentuckians also said that they have increased access to primary care, lesser missed medications due to expense, lower odds of visiting an emergency room, lower out-of-pocket spending, more outpatient visits, and higher screening for chronic conditions including diabetes, and heart disease. They also received more regular care and better care quality.

According to a report in Arstechnica by Beth Mole, "While the findings are perhaps not surprising, they offer some of the first hard data that the ACA is actually improving the health of the 20 million Americans that gained insurance under the elaborate health law. However, the authors caution that it’s just a correlation."

Yet the data collected over three years—from 2013, before the law’s Medicaid expansion had taken hold, to late 2014, a year after and again in 2015—captured stepwise improvements, with the biggest gains seen in 2015. Gradual-but-delayed improvements square with with how new coverage would roll out.

Yet the most substantial gain in the new study may be the uptick in respondents self-reporting that they’re in “excellent” health. Previous studies have found that how people describe their health is a strong predictor of their real mortality, with those describing themselves in bad shape actually closer to death.

A report published in NY TIMES informed, "This has been the central question as we’ve been watching the complex and expensive health law unfurl. We knew the law was giving people coverage, but information about whether it’s protecting people from debt or helping them become more healthy has been slower to emerge."

In its 2012 ruling, the Supreme Court made the health law’s Medicaid expansion optional for states. The resulting variation in choices makes it much easier to compare what happened in different states and draw conclusions about what effects health insurance coverage might have for the finances and health of Americans.

There are differences between Arkansas and Kentucky as well. Kentucky expanded Medicaid in a more conventional way, while Arkansas tried an innovative expansion, offering its low-income residents private insurance. But the study found only small differences between the two approaches.