New study links excessive amounts of vitamin D to onset of atrial fibrillation

While previous studies have linked vitamin D deficiency to an increased risk for cardiovascular disease, new research at the Intermountain Medical Center Heart Institute shows that too much vitamin D can lead to the onset of a dangerous heart condition known as atrial fibrillation.

17 nov 2011--Researchers at Intermountain Medical Center, the flagship facility for the Intermountain Healthcare system, studied more than 132,000 patients and found the risk of developing atrial fibrillation was two and a half times greater in those with excess levels of vitamin D compared to patients with normal levels.

Results of the study will be presented on Wednesday, Nov. 16, at the American Heart Association Scientific Sessions in Orlando, Fla.

Atrial fibrillation is a condition in which the heart's upper chambers quiver instead of beating rhythmically, which can cause blood to pool and clot. Atrial fibrillation has been linked to an increased risk of stroke, heart failure, heart attack, dementia and even Alzheimer's disease.

T. Jared Bunch, MD, a heart rhythm specialist at the Intermountain Medical Center Heart Institute and lead investigator on the study, says the findings are significant because so many Americans use vitamin supplements to promote their health.

"There are both benefits and harm to taking vitamin supplements of all kinds," says Dr. Bunch. "Our goal is to determine a safe dose and usage range so patients can understand what amount is healthy, and what amount may be toxic."

To determine if there is a correlation between too much vitamin D and increased heart risk, Dr. Bunch and his colleagues examined blood tests from 132,000 patients in the Intermountain Healthcare database at Intermountain Medical Center.

Patients did not have any known history of atrial fibrillation, and all had previously received a vitamin D assessment as part of their routine care. Patients were then placed into categories to compare levels of vitamin D: low (less than 20 nanograms per decilter), low/normal (21-40 ng/dl), normal (41-80 ng/dl), high/normal (81-100 ng/dl), and excess (more than 100).

Patients with vitamin D levels in the normal range were compared with other groups to assess their risk of developing atrial fibrillation. In patients with low, low-normal, normal and high-normal levels of vitamin D there was no increased risk of atrial fibrillation. However, in those with excess levels of vitamin D there was a significant increased risk of atrial fibrillation. Atrial fibrillation risk was two and a half times greater in patients with excess levels of vitamin D compared to those with normal levels.

The Institute of Medicine currently advises that healthy adults should be able to take as much as 4000 IU (international units) of vitamin D daily. But the reality is that doctors don't yet know how much vitamin D causes toxicity, which is why Dr. Bunch says communication between a patient and their healthcare provider is critical.

Vitamin D, which is synthesized by the body with exposure to sun, is used to regulate calcium and phosphate concentrations in the blood and is essential for growth and development, cellular health, and bone remodeling, a process where mature bone tissue is removed from the skeleton and new bone tissue is formed.

In regions where sun exposure may be limited, supplemental vitamin D may be required to maintain normal blood levels. The exact amount of vitamin D to achieve normal levels is unknown and usage varies in different regions and communities, which can cause problems, say the researchers.

Dr. Bunch stresses that patients need to tell their doctors about all of the vitamins and supplements they take, as well as all medications, in order to ensure they get the best care possible. He says this research also suggests that checking blood levels of vitamin D in patients that develop atrial fibrillation may help uncover the cause of the abnormal heart rhythm disorder.

"Patients don't think of vitamins and supplements as drugs," says Dr. Bunch. "But any vitamin or supplement that is touted as 'healing' or 'natural' is a drug and will have effects that are both beneficial and harmful. Just like any therapy, vitamins need to be taken for the right reasons and at the right doses."

More than two millions Americans suffer from atrial fibrillation. The risk of developing atrial fibrillation increases as people age. About five percent of people over the age of 80 will develop the heart disorder during their lifetime.

Provided by Intermountain Medical Center

Higher Vitamin D Supplements Advised for Older Black Women


MINEOLA, N.Y., Dec. 7 -- Because dark skin acts as a barrier to sunlight, the vitamin D supplementation recommended for postmenopausal African-American women may need to be higher, according to researchers here.
Action Points --->
Explain to interested patients that this study suggests that postmenopausal black women need higher doses of vitamin D from supplements to achieve recommended serum levels because dark skin blocks sunlight.
Black women who took 20 μg a day (800 IU) instead of the recommended daily allowance of 10 to 15 μg (400-600 IU) had a relatively rapid rise in serum vitamin D compared with a baseline period and a placebo group, John F. Aloia, M.D., of Winthrop University Hospital here, and colleagues reported in the December issue of the American Journal of Clinical Nutrition.
Nevertheless, they added, still higher amounts, ranging from 50 μg/d (2000 IU) to 70 μg/d (2800 IU) may be needed.
Reports of the dose response to vitamin D have been conflicting, and most data were derived from white men and women, while those with dark skin were generally neglected, Dr. Aloia and colleagues said.
To quantify the response in serum 25-hydroxyvitamin D concentrations, the researchers undertook a three-year study that included 208 healthy postmenopausal black women (mean age 60). All women took calcium supplements with a daily intake from all sources of approximately 1,349 mg.
Half the women were randomly assigned to consume a daily placebo, while the other half took 20 μg/d of vitamin D (800 IU) for two years, followed by 50 μg /d (2,000 IU) for another year.
Compared with the baseline period, supplementation with 20 μg/d (800 IU) of vitamin D produced a relatively rapid increase with a mean serum 25(OH)D concentration that rose from a baseline 46.9 ±20.6 nmol/L to 71.4 ±21.5 nmol/L at three months.
During the final year when the vitamin D dose was increased to 50 μg (2000 IU) a day, serum concentrations again rose, but to a lesser extent, 87.3 ±27.0 nmol/L.
Although age, weight, and body fat did not influence a woman's response, a lower baseline measure tended to increase her vitamin D response, the researchers said.
All participants achieved a serum vitamin D concentration >35 nmol/L while 95% achieved a concentration >50 nmol/L. However, they said, only 60% achieved a concentration >75 nmol/L.
The researchers also found a strong positive relationship between vitamin D and serum calcium, which suggested that vitamin D had a potentially positive effect on the availability of calcium to the body. The mean serum calcium concentration among those in the highest quartile of serum vitamin D was 0.25 mg/dL higher than that of those in the lowest quartile (P<0.0001).
However, six women in the vitamin D group had isolated episodes of mild hypercalcemia, which resolved on repeat fasting samples. Similarly, there were isolated episodes of elevated 24-hour urinary calcium excretion in three women, which resolved spontaneously in two participants, while supplements were discontinued in the other woman.
These adverse effects could lead to serious complications, such as kidney stone formation, the investigators noted.
The researchers also reported that they found no influence of increasing vitamin D intake on bone loss. African Americans differ from whites in that they have a more efficient calcium economy, their bone mass is superior to that of whites, and their risk of fracture is therefore lower, the researchers said.
Although the calcium requirement is lower among blacks than it is for white women, the optimal calcium and vitamin D status will be determined in the future by potential extracalcemic effects in protecting against hypertension, obesity, diabetes, autoimmune diseases, and certain cancers, the researchers concluded.
The investigators noted that these results may not apply to other populations. The study took place in a northern latitude so that among light-skinned women or where sun exposure is greater, seasonal adjustments would be a greater consideration.
They also said that their simplified one-measurement, one-dose adjustment algorithm gave satisfactory results, but given individual variability in responses to vitamin D, a better result would be expected if measurements were adjusted a second time.
On the basis of these findings, the researchers suggested an algorithm for prescribing vitamin D in black women. They recommended a dose of 70 μg/d (2800 IU) for those with a concentration >45 nmol/L and a dose of 100 μg/d (4000 IU) for those with a low concentration.
None of the authors reported a conflict of interest.
Primary source: American Journal of Clinical NutritionSource reference:Talward SA, et al "Dose response to vitamin D supplementation among postmenopausal African-American women" Am J Clin Nutr 2007; 86: 1657-1662.