Too Much Vitamin D! Yes, we have found a ceiling.

For a column that has spent some effort to advocate for Vitamin D and its benefits, it’s important for us to also know where our upper limit is. What is toxic? I get that question all the time and we haven’t had a clear answer. Now we do! It’s atrial fibrillation that emerges as the risk.


Atrial fibrillation is when the top part of your heart, the atrium, that is meant to prime the ventricle with a coordinated filling beat, gets spastic and effectively shivers like a little bowl of jello. In effect, it is beating 400 beats a minute which the ventricle below just can’t do. The net result is a chaotic beating of the heart with no pattern to the beat. Often it’s too fast, around 140-160 but the output of blood is actually lower because the ventricle isn’t being primed properly. You feel crummy. Younger folks will often revert back to a normal rhythm when the offending cause of their atrial fibrillation goes away – most commonly too much thyroid hormone.



Dr Bunch was the lead investigator in this study and found that folks with an excessive level of Vitamin D, greater than 100 ng, have a two and a half time increased risk of developing atrial fibrillation. The study has pretty good predictive power because they were following some 132,000 people. The comparison was to folks with “normal levels” that they defined as 40-80 ng.



Isn’t that interesting! See where we have come. A few years ago we called normal 9-50 ng because that is what we observed in the population. Now we are calling anything below 40 to be low. The Institute of Medicine is saying its safe to take up to 4000 IU a day, which is what a young 20 year old Caucasian will make in 4 minutes of good sunshine. But the IOM recommends only 600-800 IU a day for bone health. That’s way too low for heart protection. The average person taking 4000 IU a day will likely level off at around 40-50 ng. On just 2000 IU a day, the average person in Wisconsin will level off around 30-40 ng – too low.



Only 5% of the population develops atrial fibrillation in their lifetime, but it becomes much more common as we age and develop heart failure. This study becomes a bit of a caution to the Vit D enthusiasts who cheerfully take 10,000 IU a day without measuring a blood level. On 10K a day, the average person will level off at 80 ng, but some petit folks with little body fat will be much higher.



WWW. What will work for me?: I’m glad to hear the normal range being defined as 40-80 ng. That’s pretty good science. I got my level checked and I’m in the 60s. The reduction in cardiac risk with more D is pretty impressive when your level gets to 45 or so, so I like to think of that as my floor. A level of 100 is a long ways away.


Reference: American Heart Association Meetings in Orlando, Nov 18, 2011 Report from Intermountain Medical Center, Dr Jared Bunch

Avatar Written by John Whitcomb

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