Much ado has been made over the news story “Vitamin D warning: Too much can harm your heart” that appeared on MSNBC recently. As of today, 2000 people forwarded this story over email, while 1500 shared over Facebook, and who knows how many read over it in their Google News feed or MSN check in.
The story covered a presentation at the American Heart Association annual meeting. The abstract to the presentation can be found here:
Smith MB et al. Vitamin D Excess Is Significantly Associated with Risk of Atrial Fibrillation. American Heart Assocation 2011 Meeting. 2011; 124: A14699.
The investigators found in an observational study of 132,000 subjects at Intermountain Medical Center that patients with 25(OH)D serum levels greater than 100 ng/ml were at a 2.5 times greater risk of developing atrial fibrillation. They found no increased risk of developing atrial fibrillation in levels of 0-20 ng/ml, 21-40 ng/ml, 61-80 ng/ml or 81-100 ng/ml. They did find an increased risk of hypertension, heart failure, diabetes, and renal failure for those who were deficient (0-20 ng/ml).
First off, I would like to remind everyone that levels above 100 ng/ml are hard to achieve. This is well outside levels recommend by the Endocrine Society (40-60 ng/ml), Professor Heaney (48-60 ng/ml) and the Vitamin D Council (50-80 ng/ml). Also keep in mind that we know from many studies that the higher your blood levels, the more difficult it is to raise your blood levels. In other words, 1,000 IU/day increase at a baseline 25(OH)D level of 10 ng/ml will take you much further than a 1,000 IU/day increase at a baseline level of 60 ng/ml.
A 25(OH)D level of 100 ng/ml is usually achieved with intake of 10,000 IU/day or more, coupled with consistent sun exposure. As many people with absorption issues know, even then, there is still a possibility that you do not achieve vitamin D blood serum levels greater than 100 ng/ml. This is why the Vitamin D Council recommends that anyone dosing at or higher than 10,000 IU/day get their 25(OH)D tested on a regular basis to ensure they are achieving optimal levels. Regardless of this study, we feel it is important to follow the recommendations of experts, and maintain levels between 40-80 ng/ml (either following the Endocrine Society or Vitamin D Council guidelines).
The mechanism has yet to be accounted for by the investigators of the study. And many have cited that association does not necessarily translate to causation, and in consequence, we can’t take this study too seriously. However, I would like to remind everyone that to date, 25(OH)D levels recommend by experts are largely based on observational studies and human physiology, with a strong emphasis of logic placed on what levels humans evolved to maintain in response to consistent year-round full body sun exposure. To date, there are not many randomized controlled trials that even attempt to delve into the 40-80 ng/ml range, or even open studies that attempt this.
If diseases are associated with what is presumed to be deficient levels (under 40 ng/ml, based on human physiology), then it is not unreasonable to think that there are a host of diseases associated with high levels (over 100 ng/ml, perhaps lower). With this in mind, this observational study on atrial fibrillation should not come shocking or alarming. As mentioned, it is very difficult to find subjects over 100 ng/ml, so these kinds of observational studies will not come nearly as quickly as studies observing deficient subjects.
What is unfortunate here is the lack of perspective in the MSNBC article. This study is a victim of poor journalism. The title reads like a siren, warning all who take vitamin D to stop. Much to our dismay, we are sure they achieved this for a portion of readers. They also cite a figure of 600 IU recommended daily allowance, which is irrelevant to the study. People can take several thousand units higher than 600 IU of vitamin D , and not come close to 25(OH)D levels of 100 ng/ml. The Vitamin D Council recommends 5,000 IU/day for those who do not get consistent full body sun exposure. Also note the cringe inducing typo in both the MSNBC article and the abstract. It should read “ng/ml,” not “ng/dl.” We have confirmed this error with the investigators.
Lastly, we commend the approach of Intermountain Medical Center. Says one of the investigators and staff members of the IMC, Dr. Jared Bunch,
“There are definite risks with under supplementation, so we advocate serum assessment after stable dosing in our practice.”
Dr. Bunch recommends levels between 40-80 ng/ml, right in line with what we believe in.