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Vitamin D: Do you get enough?

couple sunbathing
March 7, 2016 (Updated: August 4, 2021)
Lily Moran

Vitamin D is a critically important nutrient. Though it’s considered a vitamin, it actually functions more like a hormone. Every single cell has a receptor for it, so it has far-reaching effects on your health.

In addition to its well-proven role in maintaining bone health, the so-called “sunshine vitamin” can:

  • Boost your immune system’s defenses
  • Reduce your risk of depression
  • Decrease your risk of high blood pressure, cardiovascular disease, type 2 diabetes, and stroke
  • Help delay—even prevent—cognitive decline and Alzheimer’s disease
  • Protect against several forms of cancer
  • Prevent eye diseases such as macular degeneration

The problem is, most people don’t get to experience the profound benefits of vitamin D because they’re flat-out deficient in the nutrient. In fact, vitamin D deficiency is rampant not just in the US but throughout the world. By some estimates, 1 billion people worldwide have levels considered too low.

Typical Vitamin D Deficiency Levels

In one survey of 4,495 US adults, the overall rate of vitamin D deficiency was 41.6%. African Americans fared the worst (82% were deficient) followed by Hispanics (69%). Deficiency was defined as concentrations less than or equal to 50 nmol/L or 20 ng/mL (nanograms per milliliter).

These researchers concluded, “Given that vitamin D deficiency is linked to some of the important risk factors of leading causes of death in the United States, it is important that health professionals are aware of this connection and offer dietary and other intervention strategies to correct vitamin D deficiency, especially in minority groups.”

Seems easy enough, but there’s a problem…

Current RDAs Are Too Low

One of the central players in defining vitamin D sufficiency is the Food and Nutrition Board at the Institute of Medicine (IOM).

Their suggestion for the recommended daily allowance (RDA) is 600 IU. Age, sex, health status, environmental factors, and other considerations are not taken into account. It’s just 600 IU, straight across the board.

According to a study published in 2014 in the journal Nutrients, “RDA is the nutrient intake considered to be sufficient to meet the requirements of 97.5% of healthy individuals. The RDA for vitamin D is 600 IU per day for individuals 1 to 70 years of age and is assumed to achieve [blood levels] of 50 nmol/L or more in 97.5% of healthy individuals.”

Unfortunately, with 1 billion people on our planet severely lacking in D, that amount just doesn’t seem to be cutting it. And the authors of that research paper agree…

In it, they explain that the IOM determined their RDA by looking at 10 studies that were carried out during the winter months in northern climes (to minimize the influence of sun exposure on D levels). They collected 32 study averages of D blood levels then gauged those against vitamin D intake, which yielded them an estimated dosage needed to achieve those blood levels.

In their calculations, the IOM estimated that 600 IU would achieve an average vitamin D level of 63 nmol/L and a lower prediction limit of 56 nmol/L. The latter value was rounded down to 50 nmol/L to accommodate for uncertainty.

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The study authors, however, completely disagreed with the IOM’s conclusions. Without boring you with the intricate details, they redid the IOM’s “math” and actually found that by taking 600 IU daily, 97.5% of individuals would have vitamin D blood levels closer to 26.8 nmol/L—nowhere near the adequate range of 50 nmol/L estimated by the IOM.

These researchers also wrote that “8,895 IU of vitamin D per day may be needed to accomplish that 97.5% of individuals achieve [blood levels] of 50 nmol/L or more…a dose well in excess of the current RDA of 600 IU per day and the tolerable upper intake of 4,000 IU per day.”

They concluded, “The public health and clinical implications of the miscalculated RDA for vitamin D are serious. With the current recommendation of 600 IU, bone health objectives and disease and injury prevention targets will not be met.”

This study laid the groundwork for other researchers to look into the accuracy or inaccuracy of this RDA. Most have resoundingly agreed that 600 IU is far too low to achieve any substantial benefit.

In a study published in 2017, the researcher wrote that based on all the research, “we call public health authorities to consider designating as the RDA at least three-fourths of the levels proposed by the Endocrine Society Expert Committee as safe upper tolerable daily intake doses. This could lead to a recommendation of 1,000 IU for children <1 year on enriched formula and 1,500 IU for breastfed children older than 6 months, 3,000 IU for children >1 year of age, and around 8,000 IU for young adults and thereafter. Actions are urgently needed to protect the global population from vitamin D deficiency.”

How Much Vitamin D Should You Take?

To figure out how much vitamin D you should supplement every day, the first step is to have your doctor test your levels. This is accomplished with a simple and relatively inexpensive blood test.

If your levels are in the ideal range, you should take a D supplement to help sustain those healthy levels. A good maintenance dose is 1,500 IU per day.

If your result shows you have a deficiency, you should supplement at least 5,000 IU daily. It may take several months—even up to a year—to increase your levels into the healthy range, but if you stay consistent, it will eventually happen.

You may also consider getting out in the sun more often. Vitamin D is produced in the body from exposure to the sun’s UV rays, but most Americans spend little time outdoors anymore. And when they do, they slather on the sunscreen, which prevents the UV light from penetrating the skin.

You certainly don’t want to spend hours on end baking in the sun, but 20-30 minutes per day of unprotected sun exposure should help you naturally boost your body’s ability to synthesize vitamin D.

Some foods contain vitamin D, as well, such as fortified dairy products and fatty fish like salmon.

But don’t count on food and sun exposure alone to get you where you need to be. The only surefire way to raise your levels of vitamin D is to supplement. And based on all the research, taking upwards of 5,000-8,000 IU if you are severely deficient is the way to go. As always, though, work with your doctor to determine the best dosage for you.


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