As a longtime physician, I know that having access to stable, affordable health coverage is a critical step in achieving better health outcomes.

That view is underscored in a study that appeared in today’s (May 2) New England Journal of Medicine (NEJM) on the effects of Medicaid coverage on individuals’ health and finances. Led by researchers at Harvard and MIT, the study—the Oregon Health Insurance Study—offers a good snapshot of how being insured can help low-income Americans.

Here’s the background:  In 2008, Oregon officials created a lottery giving uninsured, low-income adults a chance to apply for Medicaid. Nearly 90,000 people signed up, and approximately 30,000 were selected. By randomly providing health insurance to some, but not all, Oregon effectively established both treatment and control groups, presenting a unique opportunity to analyze the effects of having public health insurance.

The study in NEJM highlighted the latest data from the experiment. It showed that enrollment in Medicaid, after about two years, profoundly increased patients’ use of needed medical services, and vastly reduced the financial strain that previously limited their care.

The use of physician services, prescription drugs and hospitalizations increased by about 35 percent when patients had Medicaid. The probability of having a consistent place to get care, and to receive preventive services and screenings, increased by 50 percent or more.

Having Medicaid had a big impact on family finances. It virtually eliminated out-of-pocket catastrophic medical expenditures for enrolled individuals. It alleviated other measures of financial strain, such as reducing by more than 50 percent the probability of having to borrow money, or having to skip paying other bills because of medical expenses.

One of the most significant findings is that expanding Medicaid was shown to substantially reduce depression. Those who received Medicaid in the Oregon lottery reduced rates of depression by a noteworthy 30 percent compared to those who did not have coverage. This is important, because improving mental health is a powerful gateway to improving overall health.

Each of these factors demonstrates the value of health insurance coverage, but the study’s findings show that coverage alone will not necessarily lead to good health. Over two years, those who received Medicaid through the lottery were more likely to be diagnosed with diabetes than those who were uninsured, but their blood sugar levels remained about the same. The same was true for their blood pressure and cholesterol levels.

Coordinating care for complex illness—as well as adhering to new medications and reversing the effects of detrimental lifestyle choices—are all difficult to accomplish, regardless of a patient’s insurance status. Providers and patients, and our health system as a whole, must do a better job navigating these thorny issues. Various efforts are underway to improve care for those with chronic illnesses. We also know that these conditions are affected by factors unrelated to health care, such as where people live, their income and their education.

The bottom line is that better health requires health insurance coverage, but it doesn’t end there.

So far, the Oregon Health Insurance Study shows us that people who obtained Medicaid coverage received more health care services in the first two years—especially needed preventive care—and had less depression and financial worries. Their health outcomes weren’t significantly better, but at least they are now participating in the health care system and getting the care they need, without plunging their families deeper into poverty. From this vantage point, the glass seems more than half full.