What causes hardening of the arteries?

Several things: Hight blood pressure , diabetes, high cholesterol , smoking , family history of early atherosclerosis , some hypercoagulable disease like homocystenemia , vasculitis

Multiple Factors: Atherosclerosis, also known as “hardening of the arteries”, occurs when areas of the artery wall thicken in response to either increased modifiable (high LDL particle levels, smoking or high blood pressure )and non-modifiable (genetics, age, gender) risk factors. Over time, areas of focal thickening may grow into a larger lesion called a “plaque" that can limit blood flow through the vessel.