What is considered a low HDL cholesterol level?

A low HDL (high-density lipoprotein) cholesterol level is an important factor in assessing cardiovascular risk. HDL is known as "good" cholesterol because it helps remove other forms of cholesterol from the bloodstream. Typically, an HDL level of less than 40 mg/dL in men and less than 50 mg/dL in women is considered low and a risk factor for heart disease.

In this case, a level of less than 40 mg/dL is recognized as a threshold indicating low HDL cholesterol, which is why the correct answer is identified as being less than 40. The significance of maintaining a healthy HDL level is highlighted in numerous health guidelines and studies that underscore its protective role against coronary artery disease.

Recognizing the other values presented, while levels below 30 mg/dL are extremely low and suggest a serious risk, less than 40 mg/dL is the accepted cut-off for defining low HDL levels in clinical practice.