You see, research suggests we need a minimum of 3,000 IU vitamin D3 (which is the body’s preferred form) per day to achieve a total serum 25-hydroxyvitamin D—also known as 25(OH)D, the clinical biomarker measure of whole-body vitamin D status—of 30 ng/ml. 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.
Thing is, even that 30 ng/ml benchmark is really the bare minimum (because it’s the cutoff for clinical vitamin D insufficiency), which not the 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.
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 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.
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:
Anybody with limited sun exposure (i.e., anyone who spends less than the suggested 5 to 30 minutes, 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)
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.
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:
1. Suboptimal bone health
Because vitamin D aids in the absorption of calcium,* vitamin D deficiency ultimately leads to decreased calcium absorption as well as the release of calcium from the bones, sabotaging bone health and strength over time.
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 2020 review, numerous studies have identified an apparent link, noting that individuals with mood health concerns have been seen to have lower vitamin D levels.
3. 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 resilience.*
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.
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/ml is considered insufficient, anything below 20 ng/ml 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 Health. However, since we ultimately need 3,000 IU of vitamin D per day just to reach that 30 ng/ml baseline of acceptable D levels, we can’t rely on these foods alone. (A serving of cod liver oil offers just about a third of that, at 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 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.
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 often necessary if you want to get your levels up to a truly optimal place of 50 ng/ml or higher.*
