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

Josey Murray
Updated on April 8, 2022
Josey Murray
mbg Contributing Writer
By Josey Murray
mbg Contributing Writer
Josey Murray is a freelance writer focused on inclusive wellness, joyful movement, mental health, and the like.


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.

In fact, deficiency can cause quite a long list of annoying and serious issues. So, let's break down everything you need to know about vitamin D deficiency, including the telltale signs to look out for, plus what you can do to get your levels back into a healthy place.


Vitamin D is one of the most common nutrients of concern. Roughly 41% of American adults meet the criteria for clinical insufficiency and 29% for deficiency. Research suggests we need a minimum of 3,000 IU vitamin D3(which is the body's preferred form) per day, but experts recommend getting 5,000 IU in order to achieve optimal serum 25(OH)D levels.*

Who is at risk for a vitamin D deficiency?

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.

According to functional nutrition dietitian Whitney Crouch, RDN, CLT, the following people face higher risk of vitamin D deficiency:

  • People with darker skin tones, who have a reduced ability to produce vitamin D from UV rays5 because of the melanin in their skin
  • Anybody with limited sun exposure (i.e., anyone who spends less than the suggested five to 30 minutes6, three days per week, between 10 a.m. and 4 p.m., in the sun, and anyone that lives far north enough to have distinct fall and winter seasons—during which the UV strength of the sunlight is low)
  • Individuals with overweight or obesity, who have significantly increased vitamin D needs4
  • Those with health issues affecting their liver or kidneys 
  • People on low-fat diets or who don't properly absorb fat (since vitamin D is a fat-soluble vitamin)
  • People who don't regularly consume a vitamin-D-containing supplement*

The health risks of a vitamin D deficiency.

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.

"Without it, you need more dietary calcium—and most people do not meet their calcium requirements as it is," says Connie Weaver, Ph.D., a professor in Purdue University's Department of Nutrition Science.


Vitamin D deficiency can put the entire body at risk for health issues. Sufficient vitamin D is also a requirement for adequate calcium absorption in the body.

Signs & symptoms of vitamin D deficiency.

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.*

The following signs of vitamin D deficiency are among the most common:


Suboptimal bone health

Because vitamin D aids in the absorption of calcium,* vitamin D deficiency ultimately leads to decreased calcium absorption7 as well as the release of calcium from the bones, sabotaging bone health and strength over time. 


Low mood

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

In fact, according to a 2021 review8, numerous studies have identified an apparent link, noting that there is a potential positive influence of vitamin D on mental health.


Less immune resilience

Vitamin D supports a healthy and effective immune system—and research suggests that avoiding deficiency of this essential fat-soluble micronutrient is imperative when it comes to supporting your immune system function and resilience9.* 


Brain fog

Since vitamin D can support daily brain function,* falling short may leave you feeling like you're in a fog, Nicole Avena, Ph.D., an assistant professor of neuroscience at Mount Sinai School of Medicine, previously told mbg.


A few common signs of vitamin D deficiency include suboptimal bone health, mood health concerns, less immune resilience, and brain fog.

How to get more vitamin D.

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. 

Once you know your numbers, you have a couple of options for boosting your levels above that baseline of 30 ng/ml (i.e., to a minimum of 50 ng/ml, per Henderson's earlier advice).

Getting vitamin D from food.

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?)

But what about milk, you might ask? Well, it turns out that a glass of milk only provides 100 IU of vitamin D.

Meeting your vitamin D needs with supplements.*

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.*

As you supplement, work with your health care provider to test your levels a couple of times per year to ensure your efforts are paying off.


A couple ways to get more vitamin D include taking a vitamin D3 supplement and consuming vitamin D-rich foods.*

The bottom line on vitamin D deficiency.

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

Symptoms like brain fog, low mood, and suboptimal bone density can tip you off to low vitamin D levels—and supplements are necessary if you want to get your levels up to a truly optimal place of 50 ng/ml or higher.*

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.
Josey Murray author page.
Josey Murray
mbg Contributing Writer

Josey Murray is a freelance writer focused on inclusive wellness, joyful movement, mental health, and the like. A graduate of Wellesley College, where she studied English and Creative Writing, her work appears in Women’s Health, Cook & Culture, and more. By expressing her own vulnerability, she writes with warmth and empathy to help readers find self-compassion and true wellness that’s sustainable for body, mind, and planet.