A decades-long decline in LDL cholesterol rates among Americans reportedly came to a screeching halt in 2008.
Known as the "bad" cholesterol, low-density lipoprotein blood levels are a key marker of death risk from heart disease.
The revelation is based on a study conducted by Quest Diagnostics that examined the LDL blood-serum cholesterol test results of nearly 105 million Americans from 2001-2011.
"Our study is the first nationally-representative analysis to show that improvements in the United States in LDL cholesterol blood levels abruptly ended in 2008, and may have stalled since," said Harvey W. Kaufman, MD, senior medical director and investigator for Quest Diagnostics Health Trends.
Cardiovascular disease accounts for one in every three deaths in the U.S. and cholesterol, a wax-like substance, is often a key player. Cholesterol is transported to and from the cells by carriers called lipoproteins.
There are two types of lipoproteins: LDL cholesterol and high-density lipoprotein (HDL), which is known as "good" cholesterol. These two types of lipids, along with triglycerides and Lp(a) cholesterol, make up an individual's total cholesterol count.
An individual's risk for coronary heart disease rises with his blood cholesterol levels. High levels of LDL cholesterol can slowly build up in the inner walls of the arteries and cause arterial clogging, increasing an individual's risk for heart disease and stroke. Treatment options range from lifestyle modification to use of statins and other lipid-lowering medications.
A Primary Biomarker
The study, "Blood Cholesterol Trends 2001-2011 in the United States: Analysis of 105 Million Patient Records," is part of Quest Diagnostics Health Trends, a series of reports on critical health issues based on the company's clinical laboratory data.
The study appeared in the peer-reviewed, open access journal PLOS ONE in May. The investigators found a 13% decline in the annual mean LDL cholesterol level of the study population over the 11-year period. The American Heart Association considers LDL levels of 100 mg/dL or lower to be optimal.
According to the study, the average age-adjusted mean LDL levels declined from about 120 mg/dL to 104.7 mg/dL between 2001 and 2008, at which point the level plateaued and held steady for the rest of the investigative period.
The National Health and Nutrition Examination Survey (NHANES) recently released data which showed declining blood cholesterol values from 1999 through 2010. Quest Diagnostics reported similar findings but additionally found the cholesterol values stalled between 2009 and 2011, the last year considered in the study.
In addition to being the only large-scale analysis to include data from recent years, the study is also the largest to have collected data on American LDL cholesterol. The results were gathered from men and women whose tests came through Quest Diagnostics in all 50 states, including the District of Columbia, from 2001-2011.
The strengths of the study include its size, national representation, longitudinal analysis, duration and data incorporation. "Other studies that have examined population trends in LDL cholesterol have been constrained by smaller populations, shorter study periods and smaller geographical coverage," stated Kaufman.
Quest Diagnostics most likely discovered the plateau because the study reported data annually, according to Kaufman. Most recently published studies, such as the NHANES research, report results in time periods that cover multiple years.
"Other research parameters may have masked the plateau observed in our study," explained Kaufman. "The finding that LDL cholesterol levels have plateaued since 2008 is novel and has important implications for our public health."
Interpreting the Results
The first Quest Diagnostics Health Trends report, published in 2005, described a four-year trend in LDL cholesterol.
The company's most recent cholesterol study intended to update the findings in 2005. In addition, the investigators wanted to perform the study after the NHANES published data showing declining blood cholesterol values from 1999 through 2010.
"NHANES provides the context that makes the Quest Diagnostics data from the last five years so interesting," said Kaufman. "Once we looked at the Quest Diagnostics data, we were surprised at the findings."
As the investigators began their cholesterol analysis, they had no pre-existing theories regarding trends in LDL cholesterol levels. "In fact, we assumed we might find a continuation of the same trends that had occurred over the last fifty years," Kaufman said.
The observational study did not uncover the cause or causes for the LDL cholesterol plateau, however, the investigators have suggested a few hypotheses. Mainly, the study indicates that lifestyle is a big contributor to cholesterol levels.
Eating a balanced diet, getting the recommended daily dose of physical activity and properly managing stress are all crucial elements in the fight against cardiovascular disease and stroke.
Although difficult to gauge the true effect of stress on cholesterol rates, stress is commonly associated with an increase in lipids. The suddenness and the timing of the plateau suggest a link to the Great Recession, an event which also occurred abruptly around the same time period.
"Other researchers have suggested that recessions may contribute to increased stress," Kaufman shared. "And now investigators will now be challenged to understand the abrupt halting in the decline in cholesterol."
Understanding the cause of the plateau will help refocus existing strategies to address cardiovascular disease, Kaufman told ADVANCE.
Educating the Public
Quest Diagnostics investigators hope the study will encourage additional research to both identify the cause or causes of the cholesterol plateau and inform public health efforts of preventive measures. Patients need to remain engaged in their own healthcare and understand the value of regularly communicating with physicians and other healthcare providers, stated Kaufman.
"We believe the study will prompt individual patients to be more vigilant about practicing healthy behaviors," Kaufman said. "Patients should talk to their physicians about lipid-lowering medications and other appropriate treatment plans."
Given the high mortality rate from cardiovascular disease, heart health needs to remain an area of focus in this country. "Sometimes personal things like an individual's finances will affect a patient's ability to maintain a consistent treatment regimen," Kaufman observed. "Patients should talk freely, honestly and without embarrassment to their doctors regarding all possible options."