Mercury Rising
Circulation is complex, and so are the causes of high blood pressure. One contributing factor is blood volume. Blood pressure rises as blood volume increases, as if your blood vessels were a water balloon being filled. This is why a salty diet may result in high blood pressure: Sodium doesn’t travel in blood alone; it needs to be hydrated. As water floods into the blood to join the sodium, blood volume increases, causing pressure to rise. (There’s no doubt that sodium affects blood pressure, but there is conflicting research about just how much impact salt in the diet has on it.)

Another way blood pressure rises is through the narrowing of blood vessels. Just as it’s easier to drink through a big straw than a little one, blood flows more easily through larger arteries. Atherosclerosis (fat buildup on blood vessel walls), a risk factor for heart attacks and strokes, can narrow, harden, and clog blood vessels, increasing blood pressure.

Doing Damage
High blood pressure takes a toll in part because it forces the heart to struggle to keep blood flowing through your arteries. This stress can enlarge and weaken the heart. Also, as blood is forced through your blood vessels, it can damage their inner walls and lead to atheromas. These clumps of cell debris and fat can narrow the blood vessels; their accumulation is a part of atherosclerosis, which in turn causes higher blood pressure, in what can become a vicious cycle.

The eyes and kidneys are also vulnerable to high blood pressure. These sensitive organs are laced with intricate networks of blood vessels. High blood pressure can damage the delicate vessels, causing hypertensive retinopathy (eye disease) or hypertensive nephropathy (kidney disease). Kidney damage can start its own vicious cycle; as the kidneys become less adept at removing sodium and waste from the blood, the volume of blood grows, heightening pressure. In a person with diabetes, all of this adds to the extra risk that the disease already poses for the eyes and kidneys. Even if your blood glucose control is good, an eye exam or a urine test may reveal signs that high blood pressure is damaging your eyes or kidneys, respectively.