By Genevra Pittman
NEW YORK (Reuters Health) - The cholesterol levels of U.S. adults have been dropping since the late 1980's, a new study suggests - and not just because of the increased popularity of lipid-lowering drugs.
Researchers said that cholesterol, which is closely tied to heart disease risk, may be looking better because of improvements in diet, including the substitution of vegetable oils for less-healthy trans fats.
They found average total cholesterol dropped from 206 milligrams per deciliter in 1988-1994 to 196 in 2007-2010, with a similar decrease in "bad" LDL cholesterol.
"It's important and significant, the reduction that we see here, but it's not unbelievable," said Dr. Goodarz Danaei, from the Harvard School of Public Health in Boston.
"I don't think we needed a huge change in diet... to produce this change," added Danaei, who wasn't involved in the new study.
Researchers from the Centers for Disease Control and Prevention consulted nationally representative health surveys that took blood samples from adults and interviewed them on their medication use. Each survey included between 9,000 and 17,000 people.
Along with a drop in total cholesterol, Margaret Carroll and her colleagues saw average LDL levels decline from 129 to 116 between the survey periods. HDL, or "good" cholesterol, rose slightly from 50.7 to 52.5, on average.
Guidelines recommend keeping total cholesterol under 200 and LDL below 100, although 100 to 129 is still considered "near optimal."
As expected, the use of statins and other cholesterol-lowering medications increased among survey participants, from just over 3 percent to above 15 percent during the study period.
However, average cholesterol levels also fell among people who weren't on the medications, Carroll's team reported Tuesday in the Journal of the American Medical Association.
The most recent numbers suggest about one-quarter of adults age 45 and older in the U.S. are on a statin.
Danaei said the current findings support past research also showing average cholesterol is decreasing in the U.S., with a corresponding drop in heart disease. The question, he told Reuters Health, is whether cholesterol levels will continue to fall, given increasing rates of obesity.
Carroll told Reuters Health that based on this analysis, researchers "can only speculate" as to what might be causing cholesterol levels to drop.
One theory is that Americans are eating less trans fat as manufacturers cut it out of baked goods, fried food and butter-like spreads. Eating trans fat both raises LDL cholesterol and lowers HDL cholesterol.
"(The decrease) was probably due to the reductions in smoking (and) the reductions in trans fat in our diet, particularly in processed food, that have occurred over the same time period," said Donna Arnett, president of the American Heart Association, who wasn't involved in the new study.
Carroll said besides avoiding trans fats and taking any prescribed medications, people can reduce their cholesterol by limiting saturated fat intake, exercising more and losing any extra pounds.
"Everyone should know their number and seek an appropriate diet or treatment if needed," Arnett told Reuters Health.
SOURCE: http://bit.ly/JjFzqx Journal of the American Medical Association, online October 16, 2012.