Patients with diabetes need access to doctors and medicines to help them keep their disease under control. But they also need food in their pantries and enough money in their pockets to pay for necessities like rent and heat, a new study shows.

Among a group of 411 patients being treated for Type 2 diabetes in the Boston area, those who suffered from food insecurity and those who tried to save money by skimping on their meds were only half as likely as their more financially secure counterparts to be managing their disease. This disparity turned up despite the fact that in Massachusetts nearly everyone has medical insurance and prescription coverage.

The results, published Monday in JAMA Internal Medicine, underscore the fact that some aspects of health are controlled by factors outside the medical system. And yet, doctors are increasingly being held accountable when their patients miss their targets for things like blood sugar and cholesterol, the study authors noted.

It stands to reason better access to medical care ought to improve people’s health.

But clinical trials have found that things aren’t always so simple, especially for low-income patients with diabetes.

So researchers decided to look for answers at four clinics that treat diabetes patients. Two of the clinics were based at Boston’s famed Massachusetts General Hospital — one focused on diabetes care and another served general internal medicine patients — and two were community health centers in the Boston suburbs of Revere and Charleston. Study participants took a survey about their economic needs.

Among the 411 patients, only 4.1 percent lacked health insurance and 2.8 percent had no prescription coverage.

But about 40 percent of them had trouble paying for food, medicine, rent or energy, and more than 20 percent reported more than one of such “material need insecurity,” as the researchers put it.