Vitamin D- How Low Can You Go?

by Lauren Streicher, MD

Vitamin D: It’s the magical supplement pill you can purchase at your local pharmacy that prevents cancer, and reduces the risk of autoimmune diseases, chronic inflammation, multiple sclerosis, osteoporosis, heart disease, and even the flu. Or is it?

A quick Internet search would seem to confirm the many health benefits of vitamin D. But before you go out and purchase a lifetime supply, there are two things that you should know about this much-touted vitamin.

The first is that scientific research shows only one absolutely proven medical reason to take vitamin D: to facilitate the absorption of calcium that can decrease bone loss and reduce your risk of breaking a bone. Even if vitamin D doesn’t prevent cancer and chronic disease, prevention of osteoporosis is reason enough to want to maintain an adequate vitamin D level.

Which leads me to the second thing you should know about vitamin D: Experts are still debating the optimal vitamin D level to assure bone health, but also for other possible health benefits. Recommendations have ranged from the Institute of Medicine’s suggested 20 nanograms per milliliter (ng/mL), to the National Osteoporosis Foundation‘s 30 ng/mL, to the Vitamin D Council‘s 40-80 ng/mL.

Why You May Need That Vitamin D Supplement

It’s no surprise that a significant portion of the adult population has low, and sometimes really low, vitamin D levels. The winter months pretty much guarantee a deficit in many adults, since vitamin D is synthesized in the skin after exposure to sunlight.  Even if you live on the beach, getting plenty of sunshine — and therefore vitamin D — puts you at risk for melanoma, wrinkles, and sunspots. Skin problems like these make basking in the sun without a hat, sunglasses, and a high SPF sunscreen a forbidden treat. And there is not much vitamin D found naturally in food, so you can’t always improve your levels through diet.

There are other reasons that you may have low vitamin D levels. Decreased absorption of vitamin D due to gastrointestinal illness, surgery, and normal aging also can contribute to levels that are too low in your body to effectively protect your bones.

Researchers have also theorized about the connection between vitamin D levels and inflammation. But, as a July 2014 Inflammation Research review  states, “Evidence that vitamin D supplementation cures or prevents chronic disease is inconsistent.” What appears to be likely is that chronic inflammation is what leads to low vitamin D levels in the body.

Why You May Need Less Vitamin D Than You Think

The debate over vitamin D  is no small issue, since almost half of all women break a bone after menopause, and millions of women over the age of 50 are advised by their doctors to take a vitamin D supplement to get their levels up to “normal.”

A study published in the August 2015 issue of the Journal of the American Medical Association looked specifically at the serum (or  blood) levels of vitamin D needed to absorb calcium. In this randomized, double-blind clinical trial,  researchers at the University of Wisconsin at Madison gave230 postmenopausal women under the age of 75 one of the following:

  • Dailyand monthly doses of placebo pills
  • Daily 800 international units (IU) vitamin D3 with monthly placebo pills (low dose)
  • Daily placebo pills with twice monthly doses of50,000 IU vitamin D3 (high dose)

This trial lasted for four years, and the results revealed a couple of things:

First, calcium absorption increased 1 percent in the high-dose group, but decreased 2 percent and 1.3 percent  in the low-dose and placebo groups, respectively. So while supplementing with high levels of D increased calcium absorption, it wasn’t enough to deliver bone and muscle health benefits.

Second, the researchers found that the most-commonly cited recommendation, to maintain a level of at least 30 ng/mL, is not necessary for bone health.

This is a major paradigm shift, since most doctors (myself included) have routinely measured serum vitamin D levels and recommended a supplement to patients whose levels are lower than 30.

As the authors of the Wisconsin study concluded, “Study results do not justify the common and frequently touted practice of administering high- dose cholecalciferol (vitamin D3) to older adults to maintain serum [vitamin D] levels of 30 ng/mL or greater.” They suggest instead that a lower minimum level, 20 ng/mL, is adequate.

While the jury is still out on this one, it is something to consider. No, I haven’t stopped my daily vitamin D supplement (I live in cold, cloudy Chicago). But I’m certainly thinking about it.

Originally published 8/15/15