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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Study: Stroke risk and dietary vitamin D

“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.

Kojima G, Bell C, Abbott RD, Launer L, Chen R, Motonaga H, Ross GW, Curb JD, Masaki K. Low Dietary Vitamin D Predicts 34-Year Incident Stroke: The Honolulu Heart Program. Stroke. 2012 May 24.

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.

  About: John Cannell, MD

Dr. John Cannell is founder of the Vitamin D Council. He has written many peer-reviewed papers on vitamin D and speaks frequently across the United States on the subject. Dr. Cannell holds an M.D. and has served the medical field as a general practitioner, emergency physician, and psychiatrist.

8 Responses to Study: Stroke risk and dietary vitamin D

  1. Could you ask the authors about the 8000IU group? WHERE did they get that level from food!?
    IF there is a Japanese food that supplies this, it would explain all sorts of things, like longevity, etc.

    Thanks!
    Pete A

    • Brant Cebulla says:

      optionzz, I think it’s probably cod liver oil that people were taking, which the authors counted as food; which it pretty much is.

  2. Rick says:

    It would be interesting to see if other findings correlated with 25(OH)D levels: carotid plaques detected by carotid artery studies including angiograms, and whether any of these findings changed in people who had low 25(OH)D levels before starting a Vitamin D regimen. We all (even kids) shower platelet emboli, from time to time, by straining or by bumping one’s head–“seeing stars before one’s eyes,” comes from platelet emboli flowing through retinal arteries. These emboli may have launched from the internal carotid where they nested on normal endothelium or in the pits and etches of a plaque. Could Vitamin D possibly reduce the incidence of platelet emboli or clots? And if so, what is the mechanism.

  3. I was surprised that such a poor study was every published.
    Based on a single day recall of what was eaten, the study tried to tease out associations to stroke 30 years later. Those people who happened to eat some fish on the day of the survey were assumed to have higher levels of vitamin D for the rest of their lives. This is bad science. The study also failed to ever measure the vitamin D levels, amount of time in the sun, obesity,other components of the diet, etc. etc.

  4. JBG says:

    I have to agree with lahore. The study as described would not seem like a basis for concluding anything. Citing it favorably here seems like a blot on the credibility of VDC.

  5. Brant Cebulla says:

    I disagree with a couple points. First off, at no point here does Dr Cannell laud the study design. He’s just simply giving you a recap. It’s up to you to decide the merits!

    As for the merits; it’s an interesting study, but by no means telling. A lot of epidemiological studies fall into this category. Doesn’t mean it’s not worth publishing.

    The authors retrospectively looked at data, so they only had intake to look at. I’m sure if they had blood levels (which they still don’t know how to measure in 1965) and sun exposure habits, they would have gladly published those results.

  6. JBG says:

    “… when followed over 34 years, a little bit may go a long way, especially in a pool of over 7,000 participants.”

    That certainly sounds like an endorsement to me, not to mention bringing it to our attention in the first place.

    I suspect Dr. C. was so pleased by the generalities at the beginning and end of the paper that he couldn’t resist mentioning it. I can understand, but I think it was a mistake.

    • Brant Cebulla says:

      A little bit does go a long way in a pool of 7,000 in the context of statistical significance! Not sure how that’s an endorsement.

      Again, we’re just briefing the public studies published on vitamin D. Why do you think it’s a mistake to review a new study that has flaws?