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A Nutrition Scientist Explains Why A Daily Vitamin D Supplement Is So Critical

Ashley Jordan Ferira, Ph.D., RDN
August 19, 2023
Ashley Jordan Ferira, Ph.D., RDN
mbg Vice President of Scientific Affairs
By Ashley Jordan Ferira, Ph.D., RDN
mbg Vice President of Scientific Affairs
Ashley Jordan Ferira, Ph.D., RDN is Vice President of Scientific Affairs at mindbodygreen. She received her bachelor's degree in Biological Basis of Behavior from the University of Pennsylvania and Ph.D. in Foods and Nutrition from the University of Georgia.
Woman in light smiling
Image by Sophia Hsin / Stocksy
August 19, 2023

When it comes to vitamin D supplements, there are dissenters. "I eat healthy" and "I get plenty of sunshine" are the two most common reasons people give for not needing vitamin D supplementation. Unfortunately, those individuals have been misled at some point. As a nutrition scientist and registered dietitian, I'm here to clear things up..

Candidly, I'll admit that answers to some nutrition queries are kind of "TBD," like whether wheat is our friend or frenemy, or if a ketogenic diet is equally effective in men and women or prudent for the long term. But "why a vitamin D supplement is necessary" (and actually critical) for most every human is crystal clear. The answer has been demonstrated with research and in clinical practice time and time again. 

I'll let the science speak for itself. Here are four science-backed reasons you need a daily vitamin D supplement:


Vitamin D is "extra"-critical for whole-body health

Vitamin D's role in the body is sometimes minimized to calcium absorption and bone density. In reality, vitamin D is actually whole-body relevant. Fascinating and fast-moving research over the past four decades has revealed vitamin D receptors in cells and tissues throughout the body, from your brain and liver to your gut and reproductive organs, just to name a few. 

What are those receptors doing there? They are binding with vitamin D (when we nourish our bodies with vitamin D daily), orchestrating, and promoting the critical cellular and organ functions that translate to whole-body health in so many ways:

Like I said, vitamin D is essential.


"Food first" fails you in this particular instance

Vitamin D is one of the four essential fat-soluble vitamins (you know: A, D, E, K). We need to receive this micronutrient in adequate amounts daily for the myriad health functions described above. While you might think food is the answer, that's simply not the case here. Let me explain.

If dietitians had a motto, it might be "Food First." I'm not sure who started that slogan, but loads of RDs and other health experts say it with such conviction, and some people try to wield it as anti-supplement fodder. 

I'm a registered dietitian, and I'm here to say, that's a genuinely silly motto. Of course, we consume our nutrition in the form of whole foods. First and multiple times a day. But then what? Food first assumes that your food is wholly sufficient for an entire array of essential and unique macro- and micronutrients that are responsible for an array of essential and unique functions in the human body every day.

I think I prefer the Girl Scouts' motto of "Be prepared" or Gatorade's "Is it in you?" These are more relevant to nutrition, particularly given that nationally representative clinical research data9 has repeatedly and clearly demonstrated that multiple vitamins (A, C, D, E, K) and minerals (calcium, magnesium, zinc) are missing from our food (diet). We aren't consuming enough of these from our diet to achieve adequacy.

We need to mind these gaps, and for some nutrients, the food-first approach is grossly failing us. As the most widespread nutrient shortfall in our country, vitamin D is the worst victim.

You see, when we practice "food first" for vitamin D, 100% of Americans9 over the age of 2 fail to consume just 400 IU of vitamin D per day (you actually need a minimum of 3,000 IU daily to avoid vitamin D deficiency, but more on that later) from naturally occurring vitamin D food sources.

Let's fold in fortified food sources. OK, that leaves 93% of Americans9 still unable to eat their way to just 400 IU of vitamin D daily. That's about 300 million folks with a major vitamin D gap. I'd call that a nutrition emergency.

You can't eat your way to daily vitamin D sufficiency. I mean, you could...but you wouldn't want to, and it might break the bank. How about 50 glasses of milk? That will provide you with 5,000 IU of vitamin D, which is an optimal dose for most adults to achieve vitamin D sufficiency (i.e., a serum 25-hydroxyvitamin D level of 50 ng/ml or higher).

Here are some other options for the top food sources of vitamin D10 (natural or fortified), listed by order of ridiculousness, that will provide you with 5,000 IU of vitamin D:

  • 294 cubes of cheddar cheese
  • 217 sardines
  • 125 servings of canned tuna fish
  • 119 servings of liver
  • 113 large eggs
  • 62 cups of fortified cereal
  • 50 glasses of milk
  • 50 glasses of orange juice
  • 9 servings of sockeye salmon
  • 8 servings of rainbow trout
  • 7 cups of irradiated mushrooms
  • 4 tablespoons of cod liver oil

OK, so maybe the cod liver oil is semi-doable. My take on cod liver oil is that it was fine (and actually critical for basic bone health needs) when Grandma dished one dose out, but at 4 tablespoons, that's not only costly and fishy, but you have to worry about contaminants from the ocean and fish (heavy metals, mercury, dioxins, furans, PCBs) and the variable levels of vitamin D3 present.


Reliance on sun exposure is risky business

Going outside and getting some sun is not just important, it's downright healing. But relying on the sun for your daily vitamin D requirements for life is risky. Why? First, prolonged sun exposure stresses the skin, damages it, and increases risk for major skin and whole-body concerns later in life. 

Secondly, the ability of a limited range of UVB rays to hit your skin and cutaneously synthesize vitamin D3 endogenously is limited by numerous variables:

  • Regularity of sun exposure opportunities (or lack thereof)
  • Quality of sun exposure (i.e., pollution, latitude)
  • Surface area of skin available to sun exposure (i.e., sunscreen, quantity of clothing, cultural practices involving coverings)
  • Skin color, with higher melanin (darker skin tones) requiring proportionately more sun exposure
  • Age, with older age reducing the ability of skin to synthesize vitamin D3 from sun exposure

Interestingly, even when you consider all inputs (food, beverages, and sun), over 40% of U.S. adults meet the clinical criteria for vitamin D insufficiency11, a 25(OH)D level < 30 ng/ml.

Full-on deficiency is a 25(OH)D result < 20 ng/ml, and that describes the vitamin D status of nearly one-third of Americans11. Again, nutrition emergency.


The target is vitamin D sufficiency for life (not sometimes)

The purpose of a daily vitamin D supplement is to achieve vitamin D sufficiency for life. Practically, that means increasing your 25(OH)D levels in the blood well above 30 ng/ml12. Note: Total 25(OH)D is the biomarker for vitamin D status (i.e., the lab your health care provider can order).

Why 30 ng/ml? Again, below that you're clinically considered vitamin D insufficient12, and less than 20 ng/mL puts you squarely in vitamin-D-deficiency territory. Landing in either of these sub-sufficient vitamin D categories is 100% preventable, and thankfully, the solution isn't elusive.  

Pivotal pharmacokinetic research13 demonstrates that 1,000 IU of vitamin D will increase a normal-weight adult's 25(OH)D level by about 10 ng/ml. So, 3,000 IU would bump us up to 30 ng/ml (but don't stop there; this is the boundary for insufficiency), while 5,000 IU would help us achieve 50 ng/ml. That's the math.

Since we know that 93% of Americans9 are not consuming 400 IU of vitamin D from all food sources, then we can surmise that a solid 100% are also not eating their way to 3,000 IU, much less 5,000 IU per day. What can stand in the gap? A high-quality vitamin D supplement designed with potency and sufficiency in mind. 

If you want to become more intimately acquainted with your vitamin D status, plus track the success of and individualize your supplementation regimen, you can ask your health care provider to measure your serum 25(OH)D level.

Here's your vitamin D status guide:

  • Sufficiency: 25(OH)D lab result ≥ 50 ng/ml
  • Insufficiency: 25(OH)D lab result ≤ 30 ng/ml but > 20 ng/ml
  • Deficiency: 25(OH)D lab result ≤ 20 ng/ml

Again, for the sake of your health, you don't want to toy with those last two categories of vitamin D inadequacy. Sufficiency is the goal—for life. You don't want to yo-yo with vitamin D adequacy.

First, the need. Then, the solution.

Of course, deciding you need a supplement is Step 1. Then comes the actual supplement. Leveraging the full benefits of this wonderful micronutrient is wholly dependent on taking it consistently:*

Thankfully, mindbodygreen created vitamin D3 potency+, which serves up all of these paramount features in one simple gelcap per day. In addition to 5,000 IU of organic vitamin D3 per gelcap (sourced from sustainable algae), you gain the incremental benefits of unique absorption technology: a built-in trio of organic, virgin oils from avocado, flaxseed, and olives.* That way, you can take it any time of the day, with or without a meal. Now that's a smart supplement.

The takeaway

Vitamin D is an essential micronutrient with impressive pleiotropic effects in the body. Neither food intake nor regular sun exposure are evidence-based answers to the pandemic of vitamin D inadequacy.

Vitamin D sufficiency is critical for so many organ systems and whole-body health, and daily supplementation is pivotal for that mission. With vitamin D3 potency+, mission accomplished.*

If you are pregnant, breastfeeding, or taking medications, consult with your doctor before starting a supplement routine. It is always optimal to consult with a health care provider when considering what supplements are right for you.
Ashley Jordan Ferira, Ph.D., RDN author page.
Ashley Jordan Ferira, Ph.D., RDN
mbg Vice President of Scientific Affairs

Ashley Jordan Ferira, Ph.D., RDN is Vice President of Scientific Affairs at mindbodygreen. Ashley received her B.A. in Biological Basis of Behavior from the University of Pennsylvania (along with a double minor in Nutrition and Music) and Ph.D. in Foods and Nutrition from the University of Georgia. Her research contributions span vitamin D, cardiometabolic health, bone density, and weight management. Ferira is a nutrition scientist and dietitian with experience in nutrition product innovation and development, scientific affairs, education, communications, and SEO writing for global firms, including Nature Made, Metagenics, Three Ships, and mindbodygreen.

In addition to her mindbodygreen contributions, Ferira is published in Health, Metagenics Institute, American Family Physician, The Journal of Clinical Endocrinology & Metabolism, and Osteoporosis International. She has a passion for the translation of evidence-based science into innovative and high-quality products and information that help people lead healthier lives. She is a believer in compassionate, informed, and personalized approaches to nutrition, health care, and wellness. Ashley lives in beautiful Charleston, South Carolina, where she was born and raised. Whether savoring an orchestral performance or delectable meal at a local restaurant, you will find her enjoying Charleston’s cultural and culinary arts with family and friends.