7 Signs You May Have a Vitamin D Deficiency

Analysis by Dr. Joseph Mercola Fact Checked

vitamin d deficiency signs symptoms

Story at-a-glance

  • Many people are lacking vitamin D; the global prevalence of vitamin D deficiency and insufficiency is 40% to 100%
  • Vitamin D plays a role in numerous diseases, including cancer, diabetes and autoimmune diseases
  • Signs you may have a vitamin D deficiency include being over 50, having darker skin, obesity, achy bones, feeling blue, head sweating and gut trouble
  • The best way to optimize your vitamin D levels is via sun exposure; if you don’t get out in the sun regularly, a vitamin D3 supplement may be necessary
  • The only way to determine how much sun exposure is enough and/or how much vitamin D3 you need to take is to measure your vitamin D level, ideally twice a year

Vitamin D deficiency is incredibly common in the U.S., but many Americans mistakenly believe they aren't at risk because they consume vitamin D-fortified foods, such as milk. There are very few foods that have therapeutic levels of vitamin D naturally, however, and even fortified foods do not contain enough vitamin D to support your health needs.

Despite its name, vitamin D is not a regular vitamin. It's a steroid hormone that your body is designed to obtain primarily through sun exposure, not via your diet.

Just How Widespread Is Vitamin D Deficiency?

Before the year 2000, very few doctors considered the possibility of vitamin D deficiency in their patients. But as the technology to measure vitamin D became inexpensive and widely available, more research was done. It became increasingly clear that vitamin D deficiency is rampant.

According to leading vitamin D researcher Dr. Michael Holick and colleagues, the global prevalence of vitamin D deficiency (defined as a level of less than 20 ng/mL) and insufficiency (defined as a level of 20 to less than 30 ng/mL) is 40% to 100%.1

Further, 20 ng/mL has repeatedly been shown to be grossly insufficient for good health and disease prevention and, to maintain your health, levels below 40 ng/mL (100 nmol/L) are not recommended. For example, research has shown that once you reach a minimum serum vitamin D level of 40 ng/mL, your risk for cancer diminishes by 67%, compared to having a level of 20 ng/mL or less.2

Among older adults in the U.S., vitamin D deficiency may affect up to 100% of the population,3 not only because they tend to spend a lot of time indoors but also because they produce less vitamin D in response to sun exposure than a younger person with the same sun exposure.

7 Signs You May Be Vitamin D Deficient

The only way to know for sure if you're vitamin D deficient is via blood testing. However, there are some signs and symptoms to be aware of as well. If any of the following apply to you, you should get your vitamin D levels tested sooner rather than later — and optimize your levels accordingly.

1. You have darker skin — African Americans are at greater risk of vitamin D deficiency, because if you have dark skin, you need more sun exposure to produce the same amount of vitamin D as a person with pale skin. Your skin pigment acts as a natural sunscreen, so the more pigment you have, the more time you'll need to spend in the sun to make adequate amounts of vitamin D.

2. You feel "blue" — Serotonin, the brain hormone associated with mood elevation, rises with exposure to bright light and falls with decreased sun exposure. When scientists evaluated the effects of vitamin D on the mental health of 80 elderly patients, they found those with the lowest levels of vitamin D were 11 times more likely to be depressed than those with healthy levels.4

3. You're 50 or older — As mentioned, as you get older your skin doesn't make as much vitamin D in response to sun exposure as it did when you were younger. At the same time, your kidneys become less efficient at converting vitamin D into the form used by your body. Plus, older adults tend to spend a lot of time indoors, getting even less sun exposure and therefore producing even less vitamin D.

4. You're overweight, obese or have a higher muscle mass — Vitamin D is a fat-soluble, hormone-like vitamin, which means body fat acts as a "sink" by collecting it. If you're overweight or obese, you're therefore likely going to need more vitamin D than a slimmer person.5 The same holds true for people with higher body weights due to muscle mass. In one recent study, vitamin D deficiency was three times more prevalent in obese individuals.6

5. Your bones ache — According to Holick, many who see their doctor for aches and pains, especially in combination with fatigue, end up being misdiagnosed as having fibromyalgia or chronic fatigue syndrome:

"Many of these symptoms are classic signs of vitamin D deficiency osteomalacia, which is different from the vitamin D deficiency that causes osteoporosis in adults. What's happening is that the vitamin D deficiency causes a defect in putting calcium into the collagen matrix into your skeleton. As a result, you have throbbing, aching bone pain."

6. Head sweating — Also according to Holick, one of the first, classic signs of vitamin D deficiency is a sweaty head. In fact, physicians used to ask new mothers about head sweating in their newborns for this very reason. Excessive sweating in newborns due to neuromuscular irritability is still described as a common, early symptom of vitamin D deficiency.7

7. You have gut trouble — Remember, vitamin D is a fat-soluble vitamin, which means if you have a gastrointestinal condition that affects your ability to absorb fat, you may have lower absorption of fat-soluble vitamins like vitamin D as well. This includes gut conditions like Crohn's, celiac and non-celiac gluten sensitivity and inflammatory bowel disease.

Optimizing Your Vitamin D Levels to Prevent Chronic Disease

It’s now known that vitamin D is necessary not only for healthy bones but for health throughout the body. As a powerful epigenetic regulator, vitamin D influences that activity of more than 2,500 genes, and vitamin D receptors are present all over the body, including in the intestine, pancreas, prostate and immune system cells.8 Vitamin D plays a role in numerous diseases, including:9

  • Cancer
  • Diabetes
  • Acute respiratory tract infections
  • Chronic inflammatory diseases
  • Autoimmune diseases such as multiple sclerosis

An analysis by GrassrootsHealth published in PLOS ONE showed women with a vitamin D level at or above 60 ng/mL (150 nmol/L) had an 82% lower risk of breast cancer compared to those with levels below 20 ng/mL (50 nmol/L).10 Similarly, a Canadian study showed that women who reported having the most sun exposure from ages 10 to 19 had a significantly reduced risk of developing breast cancer.11 Holick noted:

"Studies have shown that if you improve your vitamin D status, it reduces risk of colorectal cancer, prostate cancer, and a whole host of other deadly cancers by 30% to 50% ... You need to realize that vitamin D is playing a very important role in helping to maintain cell growth and to help fight cancer when a cancer cell is developing in your body."

Vitamin D also fights infections, including colds and the flu, as it regulates the expression of genes that influence your immune system to attack and destroy bacteria and viruses. Further, optimizing your vitamin D levels can help protect against:

Cardiovascular disease — Vitamin D is very important for reducing high blood pressure, atherosclerotic heart disease, heart attack and stroke. One study found vitamin D deficiency leads to a 50% increase in fatal stroke.12

Autoimmune diseases — Vitamin D is a potent immune modulator, making it very important for the prevention of autoimmune diseases, like multiple sclerosis and inflammatory bowel disease.

Infections, including influenza — Vitamin D helps you fight infections of all kinds. A study done in Japan, for example, showed that schoolchildren taking 1,200 units of vitamin D per day during winter reduced their risk of getting influenza A infection by about 40%.13

DNA repair and metabolic processes — One of Holick's studies showed that healthy volunteers taking 2,000 IUs of vitamin D per day for a few months up-regulated 291 different genes that control up to 80 different metabolic processes, from improving DNA repair and immune function to having an effect on autoxidation. This is oxidation that occurs in the presence of oxygen and/or UV radiation, which has implications for aging and cancer, for example.

How Much Vitamin D Do You Need for Optimal Health?

When it comes to vitamin D, you don't want to be in the "average" or "normal" range, you want to be in the "optimal" range.

Data from GrassrootsHealth's D*Action studies suggest the optimal level for health and disease prevention is between 60 ng/mL and 80 ng/mL, with higher levels recommend for certain conditions like cancer and autoimmune disease. The cutoff for sufficiency appears to be around 40 ng/mL. In Europe, the measurements you're looking for are 150 to 200 nmol/L and 100 nmol/L respectively.

As for how to optimize your vitamin D levels, appropriate sun exposure is the best way. Personally, I haven’t taken any vitamin D for 15 years. I walk nearly every day at solar noon on my local beach. Additionally, every week I remove 60 ml of my blood and since I have an IV in I take 3 grams of magnesium chloride IV. Magnesium is a cofactor that helps your body make vitamin D.

This is why I believe I was able to reach 100 ng/ml (250 nmol/l) of vitamin D this year. That was in August and in December it dropped to 68 ng/ml. Generally, how long you need to stay in the sun to produce optimal levels of vitamin D varies greatly depending on the factors below:

Antioxidant levels and diet in general


Skin color and/or current tan level

Use of sunscreen

Latitude and altitude (elevation)

Cloud cover and pollution

Ozone layer

Surface reflection


Time of day


If your circumstances don't allow you to access the sun regularly, a vitamin D3 supplement may be necessary. Daily vitamin D3 supplementation of up to 10,000 IU may be needed to reach a vitamin D level of 40 to 60 ng/mL.

It’s important to note that vitamin D supplementation must be balanced with other nutrients, namely vitamin K2 (to avoid complications associated with excessive calcification in your arteries), calcium and magnesium.

Vitamin D Level 25 Hydroxy D

Get Your Vitamin D Levels Tested With the D*Action Project

The only way to determine how much sun exposure is enough and/or how much vitamin D3 you need to take is to measure your vitamin D level, ideally twice a year. The D*Action Project by GrassrootsHealth is a cost-effective way to do this, while simultaneously progressing valuable research.

To participate, simply purchase a D*Action Measurement Kit and follow the registration instructions included. Once you’ve confirmed your vitamin D levels via testing, remember to retest in three to four months to make sure you’ve reached your target level.

If you have, then you know you’re taking the correct dosage and/or getting the right amount of sun exposure. If you’re still low (or have reached a level above 80 ng/ml), you’ll need to adjust your dosage accordingly and retest again in another three to four months.


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