“There is a growing body of evidence that vitamin D deficiency is associated with many conditions, including hypertension, insulin resistance, diabetes mellitus, cancers, infections, autoimmune diseases, heart failure, cardiovascular diseases, and stroke.” Those are not my words but the words of Dr. Gotaro Kojima and eight colleagues from the University of Hawaii. It was great to see those words begin a paper.
Dr. Kojima studied 7,385 Japanese-American men, calculating their dietary vitamin D between 1965 and 1968. They then observed a 34-year period to see if dietary vitamin D had any effects on stroke incidence. While we all know that dietary vitamin D is close to useless, when followed over 34 years, a little bit may go a long way, especially in a pool of over 7,000 participants.
Stroke is the second leading cause of death in the USA, ranking before cancer and just after heart disease. It causes 10% of deaths, and stroke risk greatly increases after 35 years of age with two-thirds of strokes occurring in those over 65. A cardiovascular hazardous lifestyle (smoking, high blood pressure, cholesterol, diabetes, etc.) and genetics both contribute to stroke risk. Patients with atrial fibrillation have a 5% yearly risk of having a stroke. Having one stroke greatly increases your risk of another stroke.
Thus, anything that decreases the risk of stroke would be welcomed news. I wrote about a Harvard vitamin D and stroke study only a few months ago where higher vitamin D levels were found to be protective with maximal protection associated with the highest 25(OH)D levels (above 36 ng/ml) and no evidence of any U-shaped curve (higher risk with both lower and higher vitamin D levels).
In this study, Dr. Kojima in Hawaii found about a 20% increased risk of stroke in those people with the lowest vitamin D consumption, which was pretty low (0-40 IU/day). Those with the highest dietary vitamin D consumption between 160 to 8,000 IU/day, suggesting they counted cod liver oil as food. On the other hand, perhaps there is a native Japanese food, other than cold-water fatty fish, with high vitamin D content?
The authors concluded, “Vitamin D deficiency is known to be associated with cardiovascular risk factors, including hypertension, insulin resistance, diabetes mellitus, and systemic inflammation… All of these conditions could lead to accelerated atherosclerosis and subsequent cardiovascular events.”
To their credit, they suggested vitamin D supplementation as well as more studies.