4 Signs You Have A Vitamin D Deficiency — & What To Do About It

Although ample vitamin D is a must in order for your body to run as it should, it is one of the most common nutrients of concern out there.

With 41% of American adults meeting the criteria for clinical insufficiency1, and an alarming 93-plus% failing to consume just 400 IU of vitamin D per day2, it's possible you may need more of the sunshine vitamin yourself.*

You see, research suggests we need a minimum of 3,000 IU vitamin D33 (which is the body's preferred form) per day to achieve a total serum of 25-hydroxyvitamin D—also known as 25(OH)D, the clinical biomarker measure of whole-body vitamin D status—of 30 ng/ml4.

That's a whole lot more than the 400 IU per day the average person gets! Given that, it's no surprise that 29% of American adults are straight-up deficient in D. Mind you, that stat considers diet and sun, too.

Even that 30 ng/ml benchmark is really the bare minimum (because it's the cutoff for clinical vitamin D insufficiency), which is not ideal. "As an endocrinologist, I know that achieving optimal serum 25(OH)D levels in the 50+ ng/ml range is imperative for immune health, bone health, and more," says board-certified endocrinologist Brittany Henderson, M.D.

And in order to reach that 50+ ng/ml range, you actually need 5,000 IU of vitamin D per day. Here's how mbg's vice president of scientific affairs, Ashley Jordan Ferira, Ph.D., RDN breaks it down: "Pharmacokinetic research3 shows that it takes 100 IU of vitamin D to increase a normal-weight adult's serum D levels by about 10 ng/ml. So, that means that in order to achieve 50 ng/ml, you need 5,000 IU of vitamin D per day." (Read more about that here).

Basically, we're not in a good place with the sunshine vitamin—and don't let the fact that vitamin D deficiency is so common it can fool you into thinking it's not a really big deal.

Although anyone can develop a deficiency due to how widespread the vitamin D nutrient gap is, there are a few key risk factors that make a person more prone to it.

Ready for a powerful reminder not to take vitamin D deficiency lightly?

The impact of vitamin D deficiency is holistic, putting the whole body at risk of health issues, affecting bone density and immune system resilience to cardiometabolic health, to name a few, explains Crouch. 

Sufficient vitamin D is also a requirement for proper calcium absorption in the body.

Because it plays so many roles in the body (including supporting immunity, gut health, thyroid health, and more), you can bet your body will let you know when you're not getting enough vitamin D.*

A significant volume of research has been conducted on the association between low vitamin D levels and mental well-being.

If you suspect you have a vitamin D deficiency, your doctor can run a simple blood test to confirm your 25(OH)D levels.

While anything below 30 ng/ml4 is considered insufficient, anything below 20 ng/ml4 is flat-out deficient. 

When it comes to consuming more vitamin D, it is important to understand the difference between D2 and D3—especially if you follow a vegan or vegetarian diet.

While animal sources provide D3, plant sources only offer D2 (with the rare exception of algae, which contains D3), says Crouch.

Vitamin D3 is the form we produce via the sun and is the body's preferred form, which means it more effectively increases vitamin D levels in the blood, she explains. 

Given that, the most concentrated food sources of vitamin D (all of which provide D3) are cod liver oil, trout, and salmon, according to the National Institutes of Health5.

However, since we ideally need 5,000 IU of vitamin D per day just to reach our optimal 50 ng/ml levels, we can't rely on these foods alone. (A serving of cod liver oil5 offers just 1,360 IU—and who's really downing cod liver oil on a daily basis?)

When diet and sunlight alone can't supply your body with adequate vitamin D (which you now know is pretty much all the time for the average person), supplements are a must.*

While that's not true for every nutrient, it truly is the case for vitamin D. Since optimal blood vitamin D levels are between 50 and 70 ng/ml, you'll need to supplement with 5,000 IU of vitamin D3 per day to reach and maintain the ideal throughout life, Crouch says.*

Beyond that, Crouch recommends making sure you pair your supplement with healthy fats (like extra-virgin olive oil) to best absorb it.*

Many of us don't get enough vitamin D from our diet or the sun, making deficiency common.