Despite Americans’ growing girth and an increase in obesity-related diseases, cholesterol levels among adults in the United States have taken a turn downward, even in those who aren’t taking cholesterol-lowering medications such as statins, according to an analysis of national health surveys released Tuesday.
That review, conducted by the National Center for Health Statistics and the federal Centers for Disease Control and Prevention and involving more than 10,000 Americans, found a 5 percent drop in total cholesterol levels from 1988 to 2010, when the latest survey was conducted. The surveys involved in-person interviews, physical exams, and screening blood tests.
Levels of the bad kind of cholesterol, known as LDL, dropped even more — by about 10 percent — from an average blood measurement of 129 milligrams per deciliter to 116 milligrams per deciliter, according to the study that appears in the Journal of the American Medical Association. HDL cholesterol levels rose by about 5 percent, another piece of good news because high HDL levels are associated with a lower risk of heart disease.
Having an LDL measurement under 100 milligrams per deciliter is considered optimal. Current recommendations call for taking statins or other drugs when LDL levels reach at least 130 milligrams per deciliter, to lower the likelihood of heart disease in those at increased risk because of factors such as a family history or high blood pressure. Patients without risk factors are advised to start taking statins when their LDL reaches 160 milligrams per deciliter.
The study authors suspect that a sharp increase in statin use over the past two decades accounts for some of the improvement in cholesterol levels, with nearly 16 percent of Americans reporting in the most recent surveys that they take a cholesterol-lowering medication, compared with 3 percent in the earlier surveys.
But the data also indicate that adults who weren’t on statins or other drugs experienced a 7 percent decrease in LDL levels, with a corresponding increase in HDL. “I think it’s fair to say there’s something beyond drugs at work here,” said study coauthor Dr. Brian Kit, a medical epidemiologist at the National Center for Health Statistics.
American children have also experienced an improvement in cholesterol levels, according to an August study that Kit also coauthored, and few children are taking drugs to lower cholesterol levels.
While the survey analysis wasn’t designed to pinpoint reasons for the trend, Kit and his colleagues speculated that a nationwide decline in smoking and consumption of trans fats — once prevalent in margarine and baked goods — may have contributed to some improvements because smoking and trans fats have a negative impact on cholesterol levels.
Other lifestyle factors such as increased physical activity, weight loss, and a decrease in saturated fat intake probably didn’t play a major role because Americans haven’t made significant changes in those behaviors.
“Perhaps we’re eating more whole-grains rich in soluble fiber, which improve cholesterol levels,” said Joan Salge Blake, a registered dietitian at Boston University’s Sargent College of Health and Rehabilitation Sciences. The food industry began adding more whole grains to breakfast cereals and other processed foods after the government began recommending in 2005 that Americans get half their starches from whole grains.
The latest analysis didn’t examine whether Americans were actually consuming more whole grains, but Kit said it would be an interesting area for further research.
It’s also unclear, Kit said, whether the rosier cholesterol measurements are translating into improved heart health.
Government data from health surveys indicate that the prevalence of heart disease has remained steady from 1999 to 2010 for women and middle-aged men. For men older than 75, heart disease rates have edged up from 39 percent to 45 percent over that time period.
The percentage of Americans dying from heart disease and strokes, however, significantly decreased over the same period, but that could be because of better drugs to treat these conditions, rather than improved cholesterol levels.