How Much D Do You Really Need?

By David Blyweiss M.D.

How much vitamin D do you really need? If you ask the Washington DC-based Institute of Medicine (IOM), it’s not much. In fact, their new recommendation is a mere 600 IU, up from the paltry 400 IU the government had previously recommended.1

The IOM also thinks that most people are already getting enough vitamin D from the sun and their diets.

Not surprisingly, this new IOM report has a lot of people talking—and wondering if they really need to take their vitamin D supplement.

If you ask me, the answer is a resounding ‘YES!’

Hundreds of studies show the benefits of taking more—not less—vitamin D. Researchers have uncovered up to 2,000 different genes—roughly one-sixth of the human genome—that are regulated by the nutrient. Vitamin D is essential for healthy bones, a strong immune system, and good brain function as you age. It affects cell death and proliferation, as well as insulin production.

What’s most remarkable about vitamin D is the sheer number of health issues it has been linked to. In the past few years, studies have shown that a lack of the vitamin may be the primary culprit in depression, heart disease, pregnancy problems, birth defects, some cancers and multiple sclerosis.

Researchers at the University of Minnesota have also found that vitamin D levels at the start of a low-calorie diet predict weight loss success, suggesting a possible role for vitamin D in weight loss.2

Even if you aren’t overweight and don’t suffer from any of these conditions, getting more D is still a smart idea. Many of my patients report a dramatic improvement in their feeling of overall well-being after they increase their vitamin D levels to at least 1,000 IU daily.

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The problem with this IOM report is that it flies in the face of responsible research highlighting the fact that many of us simply don’t get enough D. In fact, according to the Archives of Internal Medicine, up to 77 percent of Americans are vitamin D deficient (defined as having blood levels of less than 30 nanograms per milliliter).3

Why do we come up so short, especially since vitamin D is one of the few vitamins our bodies can actually make? Sunlight converts a cholesterol-like substance naturally found in the skin into D. The problem is, where we live, our use of sunscreen and the color of our skin all impact how much vitamin D is actually made by our bodies. These are factors the IOM apparently didn’t consider when they came up with their recommendation.

If you live north of Atlanta, it’s impossible to get enough D from sunlight between October and March, no matter how exposed you are. And it’s tougher for people of color to make D—the melanin in dark skin decreases vitamin D production by up to 90 percent.

What should you do? Here’s what I tell my own patients—if you live in a sunny climate like Florida, Hawaii or the Southwest, it’s wise to take 1,000 IU daily. For those in gloomier climates like the Pacific Northwest or East Coast, increase the dosage to 2,000 IU each day. No matter where you live, it’s also smart to spend 10 to 15 minutes in the sun each day without sunscreen.

If you or your doctor suspect a true deficinecy or if you are at high risk of heart disease, cancer or depression, have your vitamin D levels tested. If you are deficient, you may need 5,000 IU or more to optimize vitamin D’s benefits.

When buying supplements or fortified foods, make sure the label reads “D3.” This is the same type the skin makes. Don’t buy any supplement containing D2. This is a plant-based form of the vitamin that the body doesn’t metabolize as easily.


  1. Dietary Reference Intakes for Calcium and Vitamin D. Institute of Medicine of the National Academies. November 30, 2010.
  2. Vitamin D linked to successful weight loss with dieting. NutraIngredients. June 12, 2009.
  3. Adit A. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Archives of Internal Medicine. 2009;169:626-632