StrokePatient friendly summary

  • UVB light may reduce the risk of stroke. However, there is little evidence that this is the case.
  • Vitamin D may reduce the risk of stroke by lowering blood pressure and preventing artery hardening.

A stroke is the rapid loss of brain function due to a disturbance in the blood supply to the brain.

A stroke is caused by either a blockage (often from a clot) or leakage (bleeding) of blood. As a result, the affected area of the brain is unable to function. This leads to the inability to move one or both limbs on one side of the body.

A person who has had a stroke may have difficulty speaking and also seeing on the affected side.

Strokes affect approximately 800,000 U.S. people annually. About 15% of strokes are caused by bleeding, and more than 50% are caused by blockage. Roughly 20% are called mini-strokes or transient ischemic attacks (TIAs). People with TIAs may not even know they have had a small stroke.

Risk factors

According to the American Heart Association/American Stroke Association, risk factors of stroke include:

  • Age, sex, low birth weight, race/ethnicity, and genetics
  • High blood pressure 
  • Pre-existing diseases: diabetes, atrial fibrillation, increased cholesterol, carotid artery stenosis, and inflammation
  • Poor diet, obesity, body fat distribution, and metabolic syndrome
  • Exposure to cigarette smoke
  • Postmenopausal hormone therapy 
  • Metabolic syndrome
  • Drug abuse

Sunlight exposure and stroke risk

Strokes are more common in winter, when solar ultraviolet-B (UVB) doses are lower. However, it is also colder in winter. Cooler temperatures raise blood pressure.

Vitamin D and stroke

Vitamin D levels

Two studies indicate that low vitamin D blood levels may increase the risk of stroke:

  • In a United Kingdom study, 77% of those who came to the hospital with a stroke had insufficient vitamin D blood levels.
  • In Germany, patients with suspected heart disease and low vitamin D blood levels also had an increased risk of stroke.

How vitamin D works

Vitamin D may reduce the risk of stroke by lowering the threat of:

  • High blood pressure
  • Coronary artery calcification or hardening (When arteries calcify, they become stiffer. This raises blood pressure.)


One study investigated the ability of vitamin D supplements to reduce stroke risk. Vitamin D had no effect on blood pressure. However, it did have a short-term benefit on the endothelial lining of the blood vessels. The endothelial lining affects blood coagulation, immune function, and control of volume and electrolyte content of the spaces in the vessels and the tissues surrounding the vessels.


There are no reported studies of using vitamin D to treat stroke.

However, increasing vitamin D levels after a stroke should help lower the risk of future strokes and other adverse health outcomes.

Find out more...

We will be adding a detailed evidence summary on this topic in the near future.  Please check back soon to find out more.

Page last edited: 17 May 2011