Looking at Vitamin D’s Role in Blood Pressure
High blood pressure is exceedingly common in the United States, occurring in one of every four people, or 75 million Americans. Vitamin D may be used to help prevent or treat high blood pressure. Only three-fourths of those who have high blood pressure are aware of their condition.
High blood pressure is a chronic medical condition discovered by measuring the pressure in one or more arteries, usually the brachial artery in the arm just below the shoulder. For the vast majority of cases (90 to 95 percent) no specific reason is known for the high blood pressure.
Explaining high blood pressure
Having your blood pressure taken is as simple as holding your arm away from your body and enduring a few seconds of squeezing. The measurement on the arm consists of two values:
A higher value, called the systolic blood pressure, which represents the maximum pressure of the blood flowing in the artery.
A lower value, called the diastolic blood pressure, which represents the minimum pressure of the blood flowing in the artery. The diastolic pressure never goes down to zero (you hope) because that means the heart is no longer pumping.
These days, a portable aneroid gauge is often used to check blood pressure. It uses a spring and air pressure to move a needle on a scale. The observer listens for the sound of blood to start and then disappear, glancing at the numbers that the needle points to on the scale. The combination of these two numbers is the blood pressure.
An abnormal blood pressure is considered to be greater than 140 systolic and/or greater than 90 diastolic. Exceptions do exist, though. For instance, a person with diabetes or kidney disease should have a blood pressure no greater than 130 over 80, written as 130/80.
High blood pressure risk factors
High blood pressure is a risk factor for many other diseases. It may be responsible for any or all of the following complications:
Aneurysm (a bulge ballooning out from the normal pipelike artery)
Stroke (loss of brain function when the blood supply to the brain is disrupted)
Kidney failure (loss of the ability of the kidney to filter the blood and to make urine)
Heart attack (also called myocardial infarction, is when the blood supply to a part of the heart is lost, leading to damage to parts of the heart and possibly heart failure)
Heart failure (inability of the heart to supply enough blood to the body)
Usually no symptoms occur with mild or moderate high blood pressure. If the blood pressure is much higher (in the range of 180 systolic and 110 diastolic), it’s accelerated high blood pressure. Symptoms such as headache and confusion may develop.
High blood pressure is a lifestyle disease, so treatment begins with weight loss and exercise. Salt reduction and increasing fruit and vegetable intake also may help for some people, whereas meditation and biofeedback have worked for others. If these treatments fail, drugs can be administered to effectively lower blood pressure to normal, but they must be taken as prescribed.
Vitamin D’s role in blood pressure
There is a strong geographic affect on blood pressure — the further one goes from the equator, the higher blood pressure gets. This suggests that high vitamin D production may protect against high blood pressure. Several large studies show that when serum 25-hydroxyvitamin D levels are high, blood pressure is low. There is some evidence that additional vitamin D will reduce blood pressure.
There aren’t yet studies that tell us the lowest effective doses for reducing blood pressure. Also, there isn’t any evidence that the effect of vitamin D on blood pressure translates to a lower risk of hypertension. Finally, it’s possible that vitamin D has nothing to do with blood pressure but that lower levels of vitamin D are indicators of people who are overweight or obese, and who do not exercise or consume a healthy diet. These are factors which are known to cause high blood pressure.
If you have high blood pressure, it may be reasonable to ask your doctor to measure your 25-hydroxyvitamin D level. Take a supplement if your serum level is less that 20 ng/ml (50 nmol/l) and see if it makes a difference in your blood pressure.
A number of potential biological mechanisms may explain why vitamin D might lower blood pressure:
Effect on the kidneys and renal glands: The kidneys indirectly control blood pressure by controlling water excretion. They do this through the help of renin, a hormone produced in the kidney. Calcitriol or vitamin D analogs are potent suppressors of the production of renin in cell and animal studies.
Effect on parathyroid hormone (PTH): PTH levels increase when dietary calcium intake or vitamin D status is low in an effort to correct calcium metabolism. Elevated PTH has a small effect to raise blood pressure, but it is uncertain how this happens. One suggestion is that PTH has a direct elevating effect on renin secretion. High vitamin D status suppresses PTH, which could indirectly suppress blood pressure.
Effect on insulin resistance: Low levels of vitamin D are associated with decreased sensitivity to insulin, which is a feature of the metabolic syndrome. The body makes excessive levels of insulin to keep the blood glucose under control. Insulin has been shown to raise blood pressure.
Direct effect on blood vessels: Vitamin D deficiency may cause increased vascular resistance, which raises blood pressure. Lack of vitamin D may also cause thickening of the walls of the blood vessels and stiffening, leading to increased blood pressure. A study showed that a single 100,000 IU dose of vitamin D to vitamin D-insufficient people improved the function of the blood vessels.