Is a low level of high density lipoprotein (HDL), or what we call “good cholesterol,” warning enough of an increased risk of heart disease? A latest study by REGARDS (Reasons for Geographic and Racial Differences in Stroke) found that while HDL is singularly linked with an increased risk of heart disease in White Americans, it alone was not a trigger among African-American adults.
The study, published in the Journal of American Cardiology, is significant, say cardiologists, noting that there is a need to look beyond a single lipid fraction. This holds particularly true among Indians. For us HDL levels matter very little in countering the effects of low-density lipoprotein (LDL) or bad cholesterol. This leads to fatty build-ups in arteries, narrowing them and increasing the risk for heart attack, stroke and peripheral artery disease.
“It is more like a combination key than a single key turning the atherosclerotic lock,” says Dr K Srinath Reddy, honorary distinguished professor at Public Health Foundation of India (PHFI).
Why Indians should be more worried about LDL, Triglycerides
“Indians have a low HDL. They say 50mg/dL HDL is ideal to neutralise LDL but in Indians, that level never crosses 45 mg/dL in the best of times. Which is why we should only focus on the LDL levels and keep them low. In fact, over the last three decades, the safe limit for LDL has been pushed down and for Indians, who are genetically prone to cardiac conditions, the LDL levels are the only concern,” says Dr Balbir Singh, Chairman, Cardiac Sciences, Cardiology, Cardiac, Electrophysiology-Pacemaker, Max Hospital, Saket.
“Internationally, they prefer LDL levels to be less than 70 mg/dL but for Indians, I would say less than 50 mg/dL. Heart disease among Indians is compounded by additional risk factors like family history, smoking, stress, hypertension and diabetes. So many young Indians are getting a stent in early ages,” he says.
The other worrisome factor is triglycerides. “LDL levels need to be reworked for some people in combination with co-morbidities, high triglycerides and body weight. Triglycerides are blood fat, which along with cholesterol, cause plaque build-up. Therefore, both triglycerides and LDL levels need to be significantly lower,” says Dr Singh.
What elevated small, dense LDL, low HDL and high triglycerides do to Indians
In the Indian context, “We have lower HDL levels as compared to the Western population and here the role of genetics, low levels of physical activity and inadequate diet have to be considered,” says Dr Ambuj Roy, Professor in Cardiology, All India Institute of Medical Sciences, New Delhi.
“However, there are sub-fractions of HDL and LDL which have different effects,” says Dr Reddy. Small dense LDL has an atherogenic effect whereas high buoyant LDL fraction does not. HDL sub-fractions too have different effects. High triglyceride levels also correlate with an elevated small, dense LDL fraction. “In metabolic syndrome, common in Indians, a combination of elevated small, dense LDL, low HDL and high triglycerides is seen. This raises the risk of vascular disease. Since small, dense LDL is not easy to measure, a high triglyceride to HDL ratio is often used as a surrogate marker for elevated small dense LDL levels,” the cardiologist points out.
According to Dr Reddy, “small, dense LDL are smaller but more densely packed with lipids. They are more numerous than big buoyant LDL particles. That’s the reason they increase the risk of atherosclerosis in the blood vessels. High levels of plasma triglycerides increase the risk of acute coronary events. Together they markedly enhance the risk of heart attacks.”
Ethnic variations in blood lipid levels and disease associations
All of these studies go to show that we should not be looking at a single lipid fraction or sub-fraction in isolation. The levels of other lipid fractions appear to modify the effects. The level of insulin resistance also matters. “The lesson we must heed is that human physiology is a complex adaptive system and a reductionist approach of chasing a single molecule seldom works,” says Dr Reddy.
HDL-elevating drugs have not helped Indians
HDL is a field actively researched and we need longitudinal studies to understand disease associations. Generally, those with low HDL levels are assumed to be at risk of heart disease. However, drugs that have been used to raise HDL levels have not shown to reduce heart disease, says Dr Roy, adding that this is a broad field and several factors are yet unexplained.
“Earlier trials of HDL elevating drugs were not successful in prevention of coronary disease,” adds Dr Reddy. Dr Bhushan Bari, senior cardiologist at Manipal Hospital, also observed that in their clinical setting, they get several patients suffering from a heart attack but they had absolutely normal HDL and LDL levels. “This only confirms that factors like lifestyle, stress and family history need to be taken into consideration rather than high LDL and low HDL levels,” he says.
(With inputs by Rinku Ghosh)