What causes high diastolic pressure in people?

Most idiopathic: Most systolic or diastolic hypertension is 'essential" (no reason, you just have it). It does run in families. There are certain unusual causes such as adrenal tumors and blockage in the arteries that supply the kidney which cause "secondary hypertension". (there is a cause.) coarctation of the aorta is another example of "correctible hypertension.".

Diastolic bp: Usually stiffening of the arteries and loss of elasticity.