Chemical determinants
Cholesterol
One important determinant of blood vessel health is cholesterol levels, with the LDL subtype of cholesterol being bad for your arteries and HDL being good.
Smoking reduces HDL.
Trans fats
Explained in poison page.
Oxidative damage
Since the brain uses about 25% of the body’s oxygen, the brain is highly susceptible to oxidative damage.
Diabetes
Diabetes damages the small blood vessels in the brain, and eventually rots these vessels to the point where they entirely close off. When this happens, the brain tissue fed by the blood vessel dies (i.e. a stroke). The diabetic brain therefore frequently looks like Swiss cheese, with lots of little holes scattered all over the place.
High blood pressure
Also damages the plumbing. High Blood Pressure ravages the small blood vessels that feed the brain, and over time leads to many little holes in your gray and white matter that are quite obvious on MRI brain scans.