Are You Getting Enough Vitamin D?
It’s well known that vitamin D is vital for keeping your bones strong as you age. But a growing number of studies suggests that the “sunshine” vitamin may also favorably affect heart health.
Strong evidence now connects low vitamin D levels to increased risks of heart attack, stroke, heart failure, and peripheral artery disease. What’s more, many people—older adults, in particular—have inadequate blood levels of vitamin D.
That said, it’s too soon for anyone to take supplements solely to thwart heart disease. Studies show a correlation between vitamin D deficiency and heart disease, but that doesn’t prove it causes heart disease. Researchers also have yet to prove that taking supplemental vitamin D can improve people’s cardiovascular outlook.
Here’s what the science says so far.
Vitamin D basics
Vitamin D is found naturally in only a few foods—mainly fatty fish like salmon, mackerel, and tuna. Many people get their vitamin D from supplements and fortified foods like milk, orange juice, and breakfast cereals.
Sunlight, the other main source, triggers the skin to synthesize a form of vitamin D that the body later converts into an active form.
Vitamin D is best known for its role in maintaining bone density, in part by helping the body absorb calcium. But it has many other functions as well: The vitamin also acts as a hormone, helping to regulate over 200 genes. Its jobs include reducing inflammation, modifying immune system activity, and influencing cell growth throughout the body.
There is debate about how much vitamin D is enough, but most experts agree that adult blood levels should be between 30 and 60 nanograms per milliliter (ng/ml). Most Americans fall short of that goal: Up to 60 percent of U.S. adults may be deficient in vitamin D, and older adults are among those at highest risk.
Age is a factor for a few reasons. Older adults often spend little time outdoors, and even when they get some sun, their bodies typically produce less vitamin D versus younger people. They also absorb less of the vitamin from food.
Being overweight can further the risk of deficiency, because fat cells store vitamin D and alter its release into the bloodstream.
Possible heart risks
Vitamin D may affect several major risk factors for heart disease. Deficiency in the vitamin alters the hormonal system that regulates blood pressure, for example. And some small studies have found that vitamin D supplements can help lower elevated blood pressure.
Deficiency may have a similar effect on cholesterol, as well—as a study led by researchers at Johns Hopkins Medicine shows. The study, published in 2016 in the Journal of Clinical Lipidology, examined more than 20,000 middle-aged and older Americans and found that almost 4,000 were deficient in vitamin D (with blood levels below 20 ng/ ml). And that group tended to have less-healthy cholesterol levels, versus people with optimal D levels of 30 ng/ml or higher.
On average, HDL cholesterol levels of the vitamin D–deficient group were 5 percent lower and their LDL cholesterol was 13 to 24 percent higher, depending on the LDL subtype. The connection remained even after the researchers factored in people’s ages, blood sugar levels, and tests of kidney function.
Many other studies have linked vitamin D deficiency with heart disease itself. One, also by Hopkins researchers, followed nearly 12,000 older Americans for roughly 20 years.
In that study, published in Atherosclerosis in 2015, white adults faced an increased risk of coronary heart disease when their vitamin D levels dropped below 17 ng/ml. Those men and women were 28 percent more likely to develop heart disease, versus people with vitamin D levels above 17 ng/ml. That was with age, weight, and exercise and smoking habits taken into account.
When the researchers investigated further, they found that high blood pressure, diabetes, and high cholesterol seemed to largely account for the link between vitamin D deficiency and coronary heart disease. That supports the theory that vitamin D may protect the heart by helping the body maintain healthier blood pressure, cholesterol, and blood sugar levels.
A complex relationship
One question is whether vitamin D deficiency affects heart disease risk in everyone, or only certain groups of people. The study described above is a case in point: Low vitamin D was linked to a higher heart disease risk for white adults, but not African Americans. That pattern has been seen in other studies as well.
The reasons are not clear, but there are some potential explanations. To diagnose vitamin D deficiency, doctors use a blood test that measures 25-hydroxyvitamin D. That is a form of vitamin D that circulates in the blood, but needs to be converted into an active form to do its job.
Studies have found that while African Americans are more likely to be deficient in 25-hydroxyvitamin D than whites, levels of active vitamin D are actually similar in both groups. So deficiency, as typically defined, may not affect all racial and ethnic groups the same way.
Researchers are also investigating the role of genes. People carry different variants of a gene that influences the amount of active vitamin D in the blood. So it’s possible that vitamin D deficiency affects people differently, depending on the gene variants they carry.
Waiting for proof
Major clinical trials are underway to test whether vitamin D supplements can reduce the risks of heart disease and stroke.
One recent preliminary trial had encouraging results: Researchers found that high-dose vitamin D—along with standard medication—seemed to modestly improve the heart’s pumping ability in patients with vitamin D deficiency and chronic heart failure.
It’s not clear, however, whether that will translate into improvements in patients’ quality of life. And until there’s more evidence, vitamin D cannot be recommended for preventing or treating heart disease. You can, however, ask your doctor to test you for vitamin D deficiency. If your levels are low, you will probably be prescribed a supplement.
In general, older adults should get at least 600 to 800 international units (IU) of vitamin D each day. But amounts of up to 2,000 IU a day may actually be optimal. Keep in mind, however, that supplemental vitamin D can build up to toxic levels and cause problems like appetite loss, fatigue, or even kidney damage. Your doctor can recommend a dosage that’s right for you.
Sun exposure, on the other hand, does not cause vitamin D toxicity. And just a short amount of time outdoors goes a long way. Spending about 10 minutes in the summer sun, without sunscreen, can supply you with 3,000 to 5,000 IU of vitamin D.