It has been demonstrated that low vitamin D is associated with blood clots (thromboses) of both small vessels and large vessels, which can cause a stroke. One study that used doses of just 35 ng/mL (a very low amount) demonstrated a significant relationship with blood clots. Other studies have confirmed this relationship.

Increasing vitamin D levels has also been successful for improving stroke outcomes and reducing damage to the blood-brain barrier and brain itself in the area of the stroke. Protecting the blood-brain barrier prevents damaging immune cells such as microglia and macrophages from harming brain tissue.

Vitamin D also causes these microglia and macrophages to calm down. They normally become active during a stroke, especially when vitamin D is deficient — a situation that worsens the damage.

What that means is vitamin D deficiency causes the brain to be even more inflamed during a stroke than it would be if the vitamin D levels were normal. This shows that high levels of vitamin D protect the brain in such cases.

It was also demonstrated that if vitamin D receptors on cell nuclei were deficient, introduction of microglia caused them to produce more harmful inflammatory cytokines, including Il-ß, IL-6 and TNF alpha. This indicates that vitamin D protects the brain from excessive immune-induced inflammation.

The same thing seems to hold true in many neurodegenerative diseases, such as multiple sclerosis, Alzheimer’s, and other brain disorders. As we age, microglia and macrophages become more harmful by producing greater amounts of the pro-inflammatory cytokines when stimulated. Low vitamin D has also been shown to make microglia less efficient at removing debris in the brain and less effective for engulfing and killing invading bacteria and viruses (a process called phagocytosis).