Often referred to as “the sunshine vitamin,” vitamin D is absorbed naturally by the body through sunlight and works together with calcium for bone health.
But as winter begins today — the winter solstice, when the Earth's axial tilt is farthest away from the sun — our bodies will receive less sunlight, which, without taking vitamin supplements, could lead to people not having enough vitamin D.
Just don't take too much.
That's what recent dietary guidelines issued by the prestigious Institute of Medicine, the health arm of the National Academy of Sciences, warned, saying super-high levels of the vitamin could be risky.
“More is not necessarily better,” cautioned Dr. Joann Manson, of Harvard Medical School, who co-authored the Institute of Medicine's report released Nov. 30.
Most people in the U.S. and Canada — from age 1 to age 70 — need to consume no more than 600 international units of vitamin D a day to maintain health, the report found. People in their 70s and older need as much as 800 IUs. The report set those levels as the “recommended dietary allowance” for vitamin D.
That's far below the 2,000 IUs a day that some scientists recommend, pointing to studies that suggest people with low levels of vitamin D are at increased risk of certain cancers or heart disease.
John Lowry, a pharmacist for area Walgreen Drug Stores, has seen an increase in vitamin D prescriptions in recent weeks, he said, ones that are typically written for about 50,000 IUs a week. Those levels are issued for people who are vitamin D deficient and may be naturally so, however; based on the Institute of Medicine's guidelines, the average consumer should take much less.
Vitamin D supplements can be bought over the counter, but purchasing them through prescriptions helps guarantee their consistency, Lowry said.
“The only difference is the FDA requires (behind the counter) drugs to be effective,” he said. “They're more consistent as far as the strength and what you get in your bloodstream.”
Certain foods can be sources for the vitamin as well, such as fatty fish, eggs, mushrooms and low-fat milk.
It can be hard to tell if you're vitamin D deficient, Lowry said. Often, the signs are similar to those of depression, and it is always best for people to visit a general practitioner on a regular basis.
As for calcium, the report recommended already accepted levels to go along with your daily D — about 1,000 milligrams of calcium a day for most adults, 700 to 1,000 mg for young children, and 1,300 mg for teenagers and menopausal women.
Most testing laboratories are using a too-high cutoff for vitamin D blood levels, said report co-author Dr. Clifford Rosen, of the Maine Medical Center. The report says at least 20 nanograms is adequate for bone health, while many labs instead list people as low if their blood levels are below 30 ng. Serious vitamin D deficiencies are diagnosed when levels dip well below 20, something that hasn't changed.
It's true that most studies link poor health to vitamin D levels that are below 20 ng, said preventive cardiologist Dr. Erin Michos, a Johns Hopkins University School of Medicine professor who wasn't part of the study.
But, “I'm not sure I'm going to dramatically change my practice,” said Michos, who pushes her patients to boost their levels until they're between 30 and 50 ng.
Lowry recommends paying attention to your vitamin D levels this winter, as well as taking other supplements.
Just don't overdo it.
“I think everybody should take a multiple vitamin,” Lowry said. But, “the rule of thumb is that if you're taking too much, it's better not to take any at all.”
Sarah Carlson can be reached at 256-740-5722 or sarah.carlson@TimesDaily.com.
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