Hypertension, or high blood pressure, means that the heart has to push harder than it should to get the blood to the entire body.

There are two blood pressure numbers: systolic (the top number) and diastolic (the bottom number). Systolic indicates the pressure at the heart’s maximum contraction, while diastolic indicates the remaining pressure when the heart is at maximum rest. Both numbers matter, and they can imply different causes.

Causes of Hypertension Generally

Most commonly, high blood pressure is linked to high cholesterol—and for good reason. High cholesterol is a good predictor of hypertension. The idea is that, much like a stiff and gunky hose will require higher water pressure to achieve the same effect, cholesterol plaques will force the heart to work harder.

This is certainly true. But correlation is not the same thing as causation—there’s a deeper cause than cholesterol: namely, what causes the damage to the blood vessels requiring higher cholesterol levels in the first place. Check out this article for more detail.

Systolic Hypertension

Elevation in the top number only, with a normal bottom number, is the most common type of hypertension with age. This is because arteries tend to stiffen with age—and the less flexible they are, the harder the heart has to work for the same effect.

Hyperthyroidism will also increase the heart rate and cardiac output, and can therefore present with this form of hypertension as well.

Diabetes can also stiffen arteries, due to Advanced Glycosylated End Products (AGEs). This can also lead to systolic hypertension.

Chronic kidney disease likewise can also present with systolic hypertension. According to this article, this is primarily due to increased blood volume when the kidney filtration is less efficient.

Diastolic Hypertension

Since diastolic blood pressure is determined by the blood vessels’ ability to relax, anything that will impair this will cause diastolic hypertension specifically. One of the most common causes of this is hypothyroidism, and specifically low T3, since T3 encourages the smooth muscles of the blood vessels to relax.

Sleep apnea can also present with diastolic hypertension. Reasons for this are unclear, but this article attributes it to “alterations in vascular function.”

Another possible cause is fibromyalgia or Chronic Fatigue Syndrome. This is because both are characterized by low levels of ATP, the body’s energy currency produced by the mitochondria, and it takes more ATP for a muscle to relax than it does for a muscle to contract. When ATP is low, among other things, the diastolic (relaxation) function of the heart suffers. This is likely why supplementing with the 5-carbon sugar called D-Ribose, one of the building blocks for ATP, helps to restore diastolic function.

The Upshot

Causes of hypertension are more varied than just cholesterol levels, though this is a common predictor.