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

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. 

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. 

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.

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).

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. 

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.

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.

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.