Americans appear to be doing a better job of managing diabetes, with more than half of diabetics reaching recommended targets for controlling blood sugar last year, according to a survey published on Saturday.

Just over a third of people had their diabetes well-controlled in 2001, according to a study of lab tests done on more than 4 million people with type 1 and type 2 diabetes.

“Control has gotten better and impressively so, but we are not there yet,” said Dr. Francine Kaufman, of the University of Southern California and past president of the American Diabetes Association, who analyzed the data.

Overall, diabetes control between 2001 and 2006 improved by 44 percent, according to the study, which was conducted by lab testing company Quest Diagnostics Inc.

Controlling diabetes is important because the condition can quietly damage blood vessels, leading to loss of toes and limbs, blindness, heart disease and death.

The study found that people with diabetes have a worse time controlling their diabetes in the winter, and that men struggle with it more than women. The results were presented on Saturday at the American Diabetes Association’s annual scientific meeting in Chicago.

About 20.8 million Americans have diabetes, which causes about 5 percent of all deaths globally each year. Most have type 2, or adult onset diabetes, in which the body loses its ability to use insulin properly.

The Quest study is based on 22.7 million lab tests that measured the average amount of sugar or glucose in a person’s blood between 2001 and 2006.

Called the hemoglobin A1C, the test can show whether a person’s blood sugar has been normal or too high over recent weeks.

Kaufman called the test a sort of report card for diabetics, with the goal of having blood sugar levels of less than 7 percent of total hemoglobin - the main protein in red blood cells.

Some studies have shown that every percentage point drop in hemoglobin A1c cuts a patient’s risk of eye, kidney or nerve-related complications by 40 percent.

Kaufman said the problem now is that the rate of improvement appears to have slowed.

“What is really tough is the last decrease in the A1c,” she said in a telephone interview. She thinks a lot of the initial decrease in blood sugar levels was related to more patients getting medications, but that will not be enough for many people to get their disease to the target level.

“People with diabetes will have to get out and get walking, lose that 5 to 10 pounds (2 to 5 kg). Just taking a pill and not doing anything else isn’t enough,” she said.

Kaufman said the study highlighted other trouble spots.

“The group with the overall poorest control is men,” she said. “One could presume they are busy trying to get ahead in the workplace and start a family.”

It also found diabetics struggle more in the winter.

“People do worse in January, February and March than they do in the summer, probably because we start overeating around Thanksgiving and don’t get serious until the sunshine begins,” she said.

The problem is that people underestimate the threat of diabetes, which Kaufman said is a big mistake.

Poorly managed type 2 diabetes, the kind linked with obesity and lack of exercise, costs the U.S. health system an extra $22.9 billion a year in direct medical costs, a recent study found.

“This is a life-taking, life-altering disease if you don’t manage it,” she said.