Researchers say people with too little or too much HDL cholesterol can have a higher risk of heart disease.

For years we’ve been told how important “good” cholesterol is to prevent heart disease.

However, new research indicates that too much of a good thing can also be bad for you.

The results have turned the conventional wisdom about cholesterol and health on its head.

It turns out that too much of any cholesterol may be bad — it’s only a matter of how much and what type.

The results were presented at the annual conference of the European Society of Cardiology (ESC Congress 2018) in Munich, Germany.

Cholesterol is a lipoprotein, a combination of fat and protein.

Unlike body fat, it doesn’t just sit around and make your clothes feel too tight.

It moves around.

“Cholesterol is essential to life,” Henry J. Pownall, PhD, scientist and medical biochemist at the Houston Methodist Research Institute in Texas, told Healthline

Pownall explains that cholesterol “is a functional component of cell membranes and plasma lipoproteins, and a precursor to steroid hormones, which regulate body function, and to bile acids, which are required for normal digestion and regulate many cell activities.”

Cholesterol is transported to where it’s needed by your blood.

It comes in two types.

Low-density lipoprotein (LDL) cholesterol is considered “bad” cholesterol because it can cause atherosclerosis, a fatty buildup in the arteries called plaque.

Plaque narrows arteries, increasing the risk for heart attack and stroke. It can also cause narrowed arteries in the legs, also called peripheral artery disease.

High-density lipoprotein (HDL) cholesterol is the “good” cholesterol.

It takes LDL cholesterol away from the arteries and moves it to the liver, where it’s broken down and passed from the body.

But, according to Pownall “While this is the conventional wisdom, at very high plasma levels, HDL may actually transfer cholesterol to the arterial wall and promote vascular disease. This is supported by cell studies and studies in mice but not humans.”

Researchers at Emory University School of Medicine in Georgia studied almost 6,000 people to discover the effect of cholesterol levels on the risk of heart attack and death.

Study participants had an average age of 63. Most already had heart disease.

Their findings showed that people with HDL (good) cholesterol levels of 41–60 mg/dl (milligrams per decilitre) had the lowest risk of heart attack or cardiovascular death.

Lower levels of HDL (less than 41 mg/dl) were associated with an increased risk.

They also discovered that the risk was significantly higher in people with high levels (greater than 60 mg/dl) of HDL cholesterol.

These people had an almost 50 percent increased risk of dying from a cardiovascular cause or experiencing a heart attack compared to those whose HDL cholesterol levels were in the 41–60 mg/dl range.

Mindy Haar, PhD, RDN, CSN, assistant dean at the School of Health Professions at the New York Institute of Technology, told Healthline “Although this research found a relationship between elevated HDL levels and heart attack risk, the findings indicate that this relationship is not necessarily a causative one but suggests the two occur together in a significant number of people.”

Haar also cautioned that more investigation is needed to clarify this relationship.

A 2017 study published in the European Heart Journal also found a strong association between high HDL cholesterol levels and increased risk of death.

More than 50,000 men and more than 60,000 women from two large population studies were include in this analysis.

The conclusion was that high HDL cholesterol levels are associated with a significantly increased risk of death from all causes, not just cardiovascular disease.

The recent Emory University study is groundbreaking because researchers focused specifically on the effect of high HDL in a population that already had heart disease.

“The study used unambiguous end points of heart attacks or death due to other cardiovascular causes. It involved a large number of participants, which gave the study good statistical power, and enough female participants were involved so that the findings applied to men and women alike,” said Pownall.

According to researchers, the results were consistent even after controlling for other risk factors for heart disease such as diabetes, smoking, alcohol consumption, race, and sex.

Researchers concluded that patients with HDL levels in the middle range had the lowest risk for heart attack or death from heart disease.

The association between high levels of HDL and increased risk of death or cardiovascular disease was also seen more frequently in women compared to men.

“It may be time to change the way we view HDL cholesterol. Traditionally, physicians have told their patients that the higher your ‘good’ cholesterol, the better. However, the results from this study and others suggest that this may no longer be the case,” Dr. Marc Allard-Ratick, a study author and an internal medicine specialist at Emory University School of Medicine, said in a press release.

Haar said don’t change your diet just yet.

“The bottom line is that this research, at this point, doesn’t change recommendations for healthy eating,” she said. “We don’t consume LDL or HDL cholesterol. These substances are created in the body.”

Haar also offers some practical advice.

“Current guidelines that have a positive effect on cholesterol levels and heart attack risk include eliminating trans fats, moderating intake of saturated fats, and focusing on the monounsaturated fats,” she said.

“We can do this by reducing intake of processed food and animal products, eating more whole plant-based foods that include fruits, vegetables, whole grains, and legumes. The bulk of our fat intake should come from monounsaturated sources such as olive oil, nuts, and avocado,” explained Haar.

Pownall notes that while patients with low HDL that’s associated with other chronic diseases will still be advised to “Lose weight, exercise more, stop smoking, and take your cholesterol and high blood pressure medication.”

However, he said, the picture is murkier for those at risk because of high HDL levels.

“High HDL as a risk factor is so new that interventions have not been validated or even proposed,” Pownall said.