Brace yourselves, dear readers: according to a shocking study in the journal JAMA Internal Medicine, health insurance may be good for your health.

Researchers at Harvard surveyed the health of nearly 9,000 low-income people in Texas, Arkansas, and Kentucky from 2013 to 2015. During this time, Arkansas and Kentucky expanded Medicaid healthcare under the Affordable Care Act while Texas did not. In the course of the study, survey respondents in Arkansas and Kentucky not only reported improvements in their access and quality of care, but were five percent more likely to report being in excellent health compared to their counterparts in Texas.

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. The data doesn’t directly prove ACA’s role in any health improvements captured. In the words of the Harvard researchers, the study design “precludes any clear causal interpretation."

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. That is, in the course of those two years, people signed up for new policies, got into doctor’s offices, and eventually started receiving new care and treatments.

By 2015, survey participants in Arkansas and Kentucky were 22.7 percent less likely than Texans to report that they had no insurance. Arkansans and Kentuckians also reported increased access to primary care, fewer skipped medications due to cost, lower out-of-pocket spending, lower chances of having an emergency room visit, more outpatient visits, and more screening for chronic conditions such as heart disease and diabetes. They also reported more routine care and higher quality of care.

These results back up other early studies that suggested people who gained health insurance coverage under the ACA had lower risks of debt from medical bills and were more likely to get routine and preventative care.

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.

Only time will tell, the authors caution, if the trends continue and lead to clear improvement in health, such as lower disease incidence and longer lifespans. The Harvard researchers also caution against using their study to generalize to the rest of the country. In the meantime, they argue that the study “provides support for staying the course” with Medicaid expansion in the two states. Their results may inform other states considering expansion.

The authors also note that Arkansas and Kentucky expanded coverage in different ways. While the former offers private options and the latter expanded Medicaid-managed care, the researchers found no significant difference between the health outcomes in the two states.

JAMA Internal Medicine, 2016. DOI: 10.1001/jamainternmed.2016.4419 (About DOIs).