Of all the common causes of disability, many people fear strokes the most. A stroke is the rapid loss of brain function due to disturbance in brain’s blood supply. This can be due to blockage or leakage of blood. As a result, one might have the inability to move the limbs, inability to talk, vision or multiple other problems. A rare but disastrous stroke causes the “locked-in” syndrome, a condition in which a patient is aware and awake but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body except for the eyes. I will always remember a man with the locked in syndrome from medical school who silently started to cry as the doctors callously talked about his “locked in” condition across his bed.
Strokes are a leading cause of adult disability in the United States and Europe and the second leading cause of death worldwide. Known risk factors for stroke include old age, high blood pressure, previous stroke, diabetes, high cholesterol, cigarette smoking and cardiac arrhythmias like atrial fibrillation. To date, high blood pressure is the most important modifiable risk factor of stroke.
A silent stroke is a stroke that does not have any outward symptoms, and the patients are typically unaware they have suffered a stroke. Despite not causing obvious symptoms, a silent stroke still causes damage to the brain, and places the patient at increased risk for major stroke in the future. Conversely, those who have suffered a major stroke are at risk of having silent strokes. A large 1998 study estimated that more than 11 million people have experienced a stroke in the United States. Approximately 770,000 of these strokes were symptomatic but 11 million (14 times more) were silent strokes, a surprisingly high differential.
Dr. Qi Sun and four colleagues from Harvard medical school recently conducted a prospective study on ischemic stroke risk and vitamin D status. In the same paper, they then ran a meta-analysis on their study and six other prospective studies that examined vitamin D and stroke.
For their own study, they identified 464 women from the Nurse’s Health Study (32,826 participants who had their blood drawn) who suffered an ischemic stroke. They then matched these 464 women with 464 controls (women who did not suffer from a stroke). From these 928 women, they found a slight, nonsignificant higher risk of ischemic stroke for those in the lowest vitamin D level tertile (median 14 ng/ml) versus those in the highest third (median 31 ng/ml). When they began adjusting for variables – like body mass index, physical activity, chronic condition and lifestyle – the association became stronger (OR 1.42, .99-2.04).
When they added their study to six other prospective cohort studies, they had 1214 stroke cases, and the associations became significant. The combined relative risk of stroke comparing low versus high vitamin D status was 1.52 (1.20-1.85). Furthermore, their model showed the lowest risk with levels above 36 ng/ml.
The authors explain the mechanisms of action,
“Consistently, animal and human experiments provide data supporting the effects of vitamin D treatment/supplementation on increasing endothelium-dependent vascular relaxation, inhibiting vascular smooth muscle cell growth, improving insulin resistance and β-cell dysfunction, inhibiting production of inflammatory cytokines, and regulating the reaction of monocytes to environmental stressors.”
The authors conclude that these findings warrant clinical trials (which are already underway) to clarify these findings. While I agree, I think this is another observational study that shows, in the meantime, it’s better to have levels over 40 ng/ml than under.