An increase in which type of cholesterol has been shown to be a risk factor for heart disease?

The correct choice is LDL, which stands for low-density lipoprotein. An increase in LDL cholesterol is widely recognized as a significant risk factor for heart disease. LDL is often referred to as "bad" cholesterol because elevated levels can lead to the buildup of fatty deposits in arteries, a condition known as atherosclerosis. This buildup can narrow the arteries and restrict blood flow, increasing the likelihood of heart attacks and strokes.

In contrast, HDL (high-density lipoprotein) is known as "good" cholesterol, as it helps to remove other forms of cholesterol from the bloodstream, potentially providing a protective effect against heart disease. Triglycerides and VLDL (very-low-density lipoprotein) also play roles in heart health, but they are primarily more closely associated with conditions like metabolic syndrome rather than being direct indicators of cardiovascular risk in the same manner as elevated LDL levels. Thus, an increase in LDL cholesterol clearly establishes a direct connection to an increased risk of heart disease.