Back in 1995, I asked one of my colleagues, a well-known researcher at the Framingham Heart Study if we could determine whether HDL (the good cholesterol) was an independent risk factor for heart disease after factoring in triglycerides (the blood fats). The median (50th percentile) level of HDL is 45 mg/dL for men and 55 mg/dL for women.
Thanks to the Framingham Heart Study, HDL was discovered to be an important risk factor for heart disease. Low levels of HDL (less than 40 in men and 50 in women) were associated with an increased risk of heart disease whereas high levels (more than 50 in men and 60 in women) were viewed as protective to the heart. In fact, some folks with high HDL may have been reassured that their heart was in great shape only to suffer a heart attack or stroke.
Now 21 years later, with a follow-up study in Framingham Offspring, we finally have a better idea why. It turns out that the risk associated with HDL is tightly linked to levels of LDL (bad cholesterol) and triglycerides (blood fats). If these levels are normal (less than 100), then a high HDL is indeed protective while a low HDL does not weigh heavily on the risk of heart disease. However, if both LDL and triglyceride levels are above 100, watch out! Not only do folks with low HDL increase their risk of heart disease (by about 60%), but the high HDLers (especially the top 1%ers) also lose their cardioprotection.
What does this mean?
- If you have a low HDL, work toward lowering high levels of LDL and triglycerides through weight loss (if overweight), blood pressure (if hypertensive), blood glucose (if diabetic or prediabetic) and do not smoke.
- If you have a high HDL, you should no longer carry around a false sense of security unless LDL and triglycerides are normal (less than 100 mg/dL) and you do not have other risk factors for heart disease.
Here is the link to our new study: