Your ZIP code can signal a lot about your health — including how consistent you are in taking your pills.

STAT wanted to know: Where in America are people most likely to take their prescription drugs? And where are they least likely?

For a window into these broader patterns, we turned to a 2016 study from the Centers for Disease Control and Prevention, which looked at 18.5 million seniors taking medication for high blood pressure. The stakes here are high: When patients don’t take these drugs as directed, they’re at elevated risk of having a stroke or heart attack, being hospitalized, and dying early.

The government researchers examined when patients filled and refilled their prescriptions, defining non-adherent patients as those who had access to their medication for fewer than 80 percent of the days after their first fill. (The seniors were all covered by Medicare’s Part D program and the data collected were from 2014.)

Those findings can be drilled down to the county level. STAT only ranked counties that have at least 50,000 people, to ensure counties with small numbers of seniors didn’t skew the findings. A handful of white counties in the upper Midwest had sky-high rates of seniors taking their medications. But in several poor rural counties in the southwest, more than 40 percent of seniors don’t regularly refill their prescriptions.

Read on to see the list:

America’s most adherent counties

  1. La Crosse County, Wis., 16.6 percent non-adherent
  1. Wood County, Wis., 16.6 percent
  1. Manitowoc County, Wis., 16.7 percent
  1. Olmsted County, Minn., 16.7 percent
  1. Otter Tail County, Minn., 16.7 percent

These upper Midwest counties have plenty of advantages that can make it easier for seniors to take their pills. Take as an example Olmsted County, Minn., which is surrounded by smaller counties with similarly good adherence.

Its residents are wealthier than most Americans, with a median household income of $68,000. That’s important, because although there are cheap generic blood pressure drugs available, patients who are financially comfortable tend to be in the habit of engaging with the health care system. Olmsted County also has plenty of rural space, but it’s densely populated enough that it’s never more than a short drive to the doctor’s office or the pharmacy.

And, crucially, Olmsted County is home to one of the world’s best-known hospitals, Mayo Clinic, which has five primary care clinics serving the county’s residents. Mayo is among the providers pushing a model of community care aimed in part at boosting medication adherence, according to Dr. Robert Stroebel, a primary care physician at Mayo. The tweaks can be simple but powerful, like making sure that everything is done consistently during an office visit and following up with calls or messages reminding at-risk patients to come back in.

“If we have a mechanism to identify those patients and engage with them, then we can hopefully readdress the issues that may be leading to their non-adherence,” Stroebel said.

America’s least adherent counties

  1. Apache County, Ariz., 45.1 percent non-adherent
  1. Maverick County, Texas,  41.8 percent
  1. Webb County, Texas, 41.7 percent
  1. McKinley County, N.M., 38.1 percent
  1. Columbus County, N.C., 38 percent

You don’t have to look far to find the challenges that make it hard for residents of these largely rural, minority-majority counties to take their pills consistently.

Consider Apache County, where seniors are nearly three times more likely than those in Olmsted County to be non-adherent to their blood pressure medications. Spanning parts of Navajo Nation and two other reservations, Apache County is three quarters American Indian — a population with high rates of high cholesterol and diabetes along with hypertension. Apache County residents live in poverty at a rate more than double that of the U.S. as a whole. And health resources are widely dispersed in a county that spreads just over 70,000 people over a landmass larger than the state of Massachusetts.

Dr. Daniel Derksen, a trained family practitioner who directs the University of Arizona’s Center for Rural Health, said that interventions to try to boost adherence won’t succeed if they don’t take these challenges into account.

After all, Derksen said, in Apache County, “it may not always be easy for individuals to access health care or get to a pharmacy — that could be an all-day endeavor across many miles of dirt roads.”

Republished with permission from STAT. This article originally appeared on August 4, 2017