Excess Vitamin D Linked to Heart Problems

Vitamin D levels higher than the low end of normal do not provide any benefits and may actually increase the risk of heart attack and other heart problems, according to new research from a Johns Hopkins University research team.

The study was led by Muhammad Amer, M.D., an assistant professor in the division of general internal medicine at the Johns Hopkins University School of Medicine. Amer and his colleague Rehan Qayyum, M.D., M.H.S., published their findings in the January 15 issue of the American Journal of Cardiology.

Amer and Qayyam examined data from more than 15,000 adult participants in the continuous National Health and Nutrition Examination Survey (NHANES), a nationally representative sample, from 2001 and 2006. People in the study undergo a range of tests, including blood tests, to evaluate their overall health and nutritional status.

The researchers looked at two measurements from blood tests: vitamin D and c-reactive protein (CRP). CRP is a factor linked to stiffening of the blood vessels and an increased risk of cardiovascular problems. CRP is produced by the liver in response to inflammation in the body. Many doctors consider a high CRP level to be a risk factor for heart disease. However, it is not known whether CRP is merely a sign of cardiovascular disease or if it actually plays a role in causing heart problems.

Amer and Qayyam discovered an interesting pattern: As vitamin D levels rose, CRP dropped – to a point. They found an inverse relationship between vitamin D and CRP in adults without cardiovascular symptoms but with relatively low vitamin D levels. Healthier, lower levels of inflammation were found in people with normal or close to normal vitamin D levels.

But as vitamin D blood levels rose above 21 nanograms per milliliter of 25-Hydroxyvitamin D –considered the low end of the normal range for vitamin D – so did CRP levels. Any additional increase in vitamin D was associated with an increase in CRP.

“The inflammation that was curtailed by vitamin D does not appear to be curtailed at higher levels of vitamin D,” Amer said. “Clearly vitamin D is important for your heart health, especially if you have low blood levels of vitamin D. It reduces cardiovascular inflammation and atherosclerosis, and may reduce mortality, but it appears that at some point it can be too much of a good thing.”

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that has long been linked with bone health. There’s growing evidence that vitamin D also plays an important role in heart and blood vessel (cardiovascular) health. Several studies have linked low levels of vitamin D with higher risk of heart disease. Vitamin D insufficiency has also been linked to other health problems, many of which – such as diabetes and obesity – are themselves risk factors for heart disease.

This growing body of research comes with increasing realization that many people may not be getting enough Vitamin D. Vitamin D occurs naturally in only a few foods, although some foods are fortified with vitamin D, including milk, some breakfast cereals, and some orange juice.

The sun is the primary source of vitamin D. But during winter months, especially in northern climates, most people do not get enough sun exposure to make enough of the vitamin. Insufficiency may persist even during the summer months, as people become more aware of the sun’s dangers and use sunscreens to help prevent skin cancers and skin damage.

Vitamin D from the sun, foods, or supplements is inactive or inert. To use it, your body must convert it into its active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol. Conversion requires a two-step process that occurs first in the liver and then the kidney.

Is More Better?

As information has accumulated about vitamin D’s health benefits, many people have started taking vitamin D supplements. Doctors prescribe vitamin D supplements for patients from newborns to post-menopausal women. Older women may be getting vitamin D from calcium supplements and taking additional large doses of the vitamin as they attempt to prevent or slow osteoporosis. And healthy people in all age groups have started self-dosing with the vitamin.

However, not all of the evidence suggests that vitamin D supplements are needed — or helpful. A 2008 review of available evidence about vitamin D and cardiovascular health was equivocal, with investigators concluding that “more research needs to be done to determine the just how much influence vitamin D might have on heart health.” That research has continued – with mixed results.

In 2010, for an Institute of Medicine report on calcium, vitamin D and health, an expert panel reviewed existing evidence on the health effects of vitamin D. The panel summarized their findings in their report brief: “This thorough review found that information about the health benefits beyond bone health—benefits often reported in the media—were from studies that provided often mixed and inconclusive results and could not be considered reliable.”

In addition, the IOM committee members concluded, “the majority of Americans and Canadians are receiving adequate amounts of both calcium and vitamin D. Further, there is emerging evidence that too much of these nutrients may be harmful.”

How Much is Enough?

These conflicting findings, said Amer, spurred him to investigate optimal levels of vitamin D and heart health. “With the confusion in the literature about the beneficial effects [of vitamin D], we wanted to know why it is  not beneficial for heart health in the long run,” he explains. “It seems like it enhances inflammation after a certain range, which we have shown for the first time.”

Amer said his findings suggest that while adequate vitamin D levels are important to heart health, the optimal range is narrow – and toward the low end of what is considered normal. However, he said, the biological and molecular mechanisms that lead  to the loss of cardiovascular benefits are unclear.

Consumers should exercise caution before taking supplements and physicians should know the potential risks of supplementation, Amer said. Each 100 international unit of vitamin D ingested daily produces about a one nanogram per milliliter increase in 25-Hydroxyvitamin D levels in the blood.

“People taking vitamin D supplements need to be sure the supplements are necessary,” Amer said. “Those pills could have unforeseen consequences to health even if they are not technically toxic.”

It’s important that that people who do choose to take the supplements get their blood levels checked regularly. “Do not just keep taking it,” Amer said in an email. “You should get your levels checked periodically because it seems to lose its beneficial effects and may be harmful after a certain range.”

Do I Need a Vitamin D Supplement?

Who might benefit from vitamin D supplements? Should you be reaching for vitamin-D fortified foods?

Before you start taking a Vitamin D supplement, said Amer, get your vitamin D blood level tested. Some people – for example, people with dark pigmentation living in urban environments in northern states and who spend little time outside in the northern – are at risk of deficiency. But everyone processes vitamin D differently.

Elevated levels of vitamin D are known to cause kidney and tissue damage, the committee said. They provide some basic guidelines for how much vitamin D you should be getting in your daily diet, based on minimal sun exposure. These recommendations were developed with the assumption that people would receive minimal sun exposure:

It’s important to remember that these are general guidelines. Some people might benefit more from from vitamin D supplements or consuming foods fortified with vitamin D. Others might not need to supplement at all, depending on how much they’re exposed to the sun and how their body metabolizes the vitamin.  Amer cites preliminary results from other research that suggest people whose vitamin D levels are already below normal might benefit more from supplements than people with normal levels.

At least in the U.S., Vitamin D is being added to more foods (e.g. orange juice, breakfast cereals), is this a concern? Or is it a good move in terms of population health? ( Generally it is good, especially for the ones in the urban/metropolitan areas with lack of physical activity and sun exposues. But again we  would not know unless you get your blood test done to know where you are).

Amer’s take-home message? “If you’re taking a vitamin D supplement, do not just keep taking it. Get your levels checked periodically, because it seems to lose its beneficial effects and may be harmful after a certain range.”

References

Amer, M. (2012, January 7). email interview.

Amer, M. & Qayyam, R. (2012). Relation Between Serum 25-Hydroxyvitamin D and C-Reactive
Protein in Asymptomatic Adults (From the Continuous National Health and Nutrition Examination Survey 2001 to 2006). Am J Cardiol;109:226 –230.

Institute of Medicine. (2010). Dietary Reference Intakes for Calcium and Vitamin D. Report Brief. http://www.iom.edu/Reports/2010/Dietary-Reference-Intakes-for-Calcium-and-Vitamin-D/Report-Brief.aspx

National Institutes of Health. Office of Dietary Supplements. (2011). Dietary Supplement Fact Sheet: Vitamin D. Retrieved from http://ods.od.nih.gov/factsheets/vitamind

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