Vitamin D Deficiency: Symptoms, Testing & Natural Sources

You leave for work before the sun is fully up. You spend most of the day indoors. By the time you finish work, the sun may already be going down.

Or maybe it's winter, when the days are shorter and getting consistent sunlight feels nearly impossible.

Most people don't think much about vitamin D until it shows up on a blood test.

In my practice, about 7 in 10 patients whose vitamin D levels I've reviewed were below 20 ng/mL. That's what I see in my own patients, not a number for everyone, since people usually get tested for a reason. Still, it has made vitamin D a conversation I have much more often than you might expect.

And there is an important reason to have that conversation.

Vitamin D is naturally present in relatively few foods, and our bodies rely partly on sunlight to produce it.[1]

For someone who spends most of the day indoors, works nights, gets limited sun exposure, or simply doesn't eat many vitamin D-rich foods, getting enough may not be as automatic as it sounds.

The answer, however, is not to assume that every symptom means you are vitamin D deficient or to start taking a high-dose supplement on your own.

Here is what is actually worth knowing.

What Does Vitamin D Actually Do?

Vitamin D is sometimes called the "sunshine vitamin" because your skin can produce it when exposed to ultraviolet B, or UVB, radiation from sunlight.

But vitamin D is much more than something we get from being outdoors.

One of its best-established roles is helping the body absorb calcium and supporting healthy bones. Vitamin D also plays a role in normal muscle, nerve signaling, and immune function. Long-term, severe vitamin D deficiency can contribute to weakened bones. In adults, severe deficiency can cause osteomalacia, a softening of the bones associated with bone pain and muscle weakness.[2]

That does not mean taking more vitamin D will automatically give you more energy, prevent illness, improve your mood, or fix every ache and pain.

Vitamin D is important, but it is not a cure-all.

Why Are So Many People Concerned About Low Vitamin D?

You might wake up, get into your car, work eight or more hours inside, drive home, make dinner, and go to bed. Someone working a night shift may have even fewer opportunities for regular daytime sun exposure.

That matters because limited sun exposure is one recognized risk factor for inadequate vitamin D status. NIH specifically includes people with occupations that limit sun exposure among groups who may be less likely to obtain adequate vitamin D from sunlight.[1]

Research has also found lower average vitamin D levels among shift workers compared with non-shift workers, although individual risk varies and shift work alone does not prove that someone is deficient.[3]

Winter can make the situation more complicated.

Vitamin D production from sunlight is affected by several things, including:

• Season

• Time of day

• Length of the day

• Cloud cover

• Skin pigmentation

• Age

• How much skin is exposed

• Geographic location

• How much time you actually spend outdoors

Even sitting beside a sunny window isn't the same thing. UVB radiation needed for vitamin D production does not penetrate glass effectively.[1]

This is also why there is no universal rule like, "Spend 15 minutes outside every day and your vitamin D will be fine."

There are simply too many variables.

And because UV exposure also increases skin cancer risk, trying to correct a possible vitamin D deficiency through excessive unprotected sun exposure is not a good strategy.[1]

Who Is More Likely to Have Low Vitamin D?

Anyone can have inadequate vitamin D, but certain circumstances can make it more likely.

You may want to discuss vitamin D with your healthcare provider if you:

• Spend most of your time indoors

• Work nights or rotating shifts

• Rarely expose your skin to sunlight

• Are an older adult

• Have darker skin

• Have a condition that affects nutrient or fat absorption, such as celiac disease, Crohn's disease, or ulcerative colitis

• Have obesity or have undergone gastric bypass surgery

• Have certain kidney or liver conditions

• Take medications that can affect vitamin D levels

• Eat very few foods containing or fortified with vitamin D

These are risk factors, not a diagnosis.[1]

You can have several risk factors and still have an adequate vitamin D level. You can also have low vitamin D without noticing anything unusual.

What Are the Symptoms of Vitamin D Deficiency?

This is where online information can become misleading.

Search for "vitamin D deficiency symptoms" and you may find enormous lists blaming low vitamin D for everything from fatigue and hair loss to weight gain, depression, poor sleep, and frequent illness.

The problem is that many of those symptoms are nonspecific.

Fatigue, for example, can have many possible causes. Poor sleep, anemia, thyroid problems, medication effects, stress, nutritional deficiencies, hormonal changes, and other health conditions can all play a role.

So feeling tired does not tell us that your vitamin D is low.

In fact, vitamin D deficiency may not cause obvious symptoms at all.

When deficiency becomes severe enough to affect bone health, recognized signs can include bone pain, muscle weakness or aches, weak bones, and fractures.[2]

This is why symptoms should be treated as clues rather than conclusions.

How Do You Know If Your Vitamin D Is Low?

When vitamin D testing is medically appropriate, the primary blood test used to assess vitamin D status is called 25-hydroxyvitamin D, often written as:

25(OH)D

This test reflects vitamin D coming from your diet, supplements, and what your body produces through sun exposure.[1]

You may see your result reported in ng/mL.

According to the Food and Nutrition Board thresholds summarized by NIH:

• Under 12 ng/mL is considered deficient.

• 12 to 19 ng/mL is called inadequate.

• 20 ng/mL and above is enough for most people.

• Levels above 50 ng/mL may be associated with harmful effects.[1]

In this article, "low" means below 20 ng/mL.

However, interpretation is not always as simple as finding one "perfect" number.

Laboratories and healthcare organizations may use somewhat different reference ranges, and your medical history matters. Your result should be interpreted in context rather than treated as an isolated number.

Does everyone need a vitamin D test?

No.

This is another area where more testing is not automatically better.

Current clinical guidance does not recommend routine vitamin D screening for every healthy adult without another reason for testing. Testing may be more appropriate when a person has certain symptoms, medical conditions, risk factors, or another clinical indication.[4]

So rather than saying, "Everyone should get their vitamin D checked," I prefer:

Ask whether checking it makes sense for you.

Where Can You Get Vitamin D Naturally?

One challenge with vitamin D is that there simply aren't many foods that naturally contain large amounts of it.

Some of the better dietary sources include:

Fatty fish Salmon, trout, tuna, and mackerel naturally contain vitamin D.

Fish liver oils Fish liver oils, including cod liver oil, can naturally provide vitamin D.

Egg yolks Egg yolks contain smaller amounts of vitamin D.

Mushrooms Certain mushrooms provide vitamin D, and UV-treated mushrooms may contain considerably more.

Fortified foods In the United States, a significant amount of dietary vitamin D comes from foods that have vitamin D added to them rather than foods that naturally contain it.

Depending on the product, these may include:

• Cow's milk

• Fortified plant-based milks

• Some breakfast cereals

• Some orange juices

• Certain yogurts and other fortified foods

Always check the nutrition label because fortification varies by brand.[1]

What About Cod Liver Oil for Vitamin D?

Cod liver oil has been used as a nutritional source of vitamin D for generations, and there is a legitimate nutritional reason behind that history.

Fish liver oils are among the natural food sources of vitamin D.[1]

Cod liver oil can also provide omega-3 fatty acids and vitamin A, depending on the specific formulation.

But that last point is important.

Cod liver oil is not simply "vitamin D in a bottle."

Different cod liver oil products can contain very different amounts of vitamin D, vitamin A, EPA, and DHA. That means the serving size and Supplement Facts label matter.

If you're already taking a multivitamin, prenatal vitamin, vitamin D supplement, fish oil, or another supplement containing vitamin A or D, adding cod liver oil without looking at your total intake could mean you're taking more than you realize.

This is especially important during pregnancy because excessive intake of preformed vitamin A (the active form found in cod liver oil, liver, and many supplements, not the beta-carotene in carrots) can be harmful to a developing baby.[1]

So when someone asks me:

"Should I take cod liver oil for vitamin D?"

My answer isn't automatically yes or no.

My first questions are:

What are you already taking? What does your diet look like? Why are you considering it? And how much vitamin A and vitamin D are actually in the product?

How Much Vitamin D Do Adults Need?

For generally healthy adults, the daily target, called the Recommended Dietary Allowance (RDA), is:

Adults ages 19–70: 600 IU (15 mcg) per day Adults age 71 and older: 800 IU (20 mcg) per day

Labels use both units, and 40 IU equals 1 mcg. These recommendations assume minimal sun exposure.[1]

To picture what that looks like in food, here are some approximate amounts:

Amounts vary by brand and preparation, so always check the label.[1]

But an RDA is not the same thing as a treatment dose for someone who has a documented deficiency.

If a person truly has vitamin D deficiency, the appropriate amount may depend on their current level, medical history, medications, diet, and other factors.

That's why copying someone else's supplement dose from social media isn't a great strategy.

More Vitamin D Is Not Always Better

Vitamin D is fat-soluble, which means excessive supplemental intake can accumulate and become harmful.

Too much vitamin D can cause excessively high calcium levels in the blood. In severe cases, vitamin D toxicity can contribute to kidney damage and other serious complications. Vitamin D toxicity is typically caused by excessive supplement intake, not normal food intake or ordinary sun exposure.[2]

For adults, the established safe upper limit (called the Tolerable Upper Intake Level) is generally 4,000 IU (100 mcg) per day from all sources unless a healthcare professional has recommended something different for a specific medical reason.[1]

That doesn't mean 4,000 IU is the amount everyone should take.

It means you shouldn't confuse an upper limit with a daily goal.

If you are taking several supplements, check the labels. Vitamin D can appear in multivitamins, bone-health formulas, immune products, calcium supplements, cod liver oil, and standalone vitamin D products.

Those amounts can add up.

As pharmacists, we also check how your vitamin D and calcium fit with your prescriptions, because timing and combinations matter.

Before You Buy Another Vitamin D Supplement

Vitamin D comes from sunlight, food, and supplements when appropriate, and the right mix is different for each person. Someone who eats fatty fish regularly and spends time outdoors may have very different needs from someone who works overnight, sleeps during the day, and eats few vitamin D-containing foods. Someone with an absorption disorder may have another set of considerations entirely.

If you're concerned about vitamin D deficiency, start with a few simple questions. Save or print this checklist:

☐ How much time do I realistically spend outdoors? Not how much sunlight you think you get. How much time are you actually outside?

☐ Do I regularly eat foods containing vitamin D? Look at your usual week, not your best day.

☐ Am I already taking vitamin D without realizing it? Check your multivitamin, calcium supplement, cod liver oil, prenatal, and other products.

☐ Do I have risk factors that make low vitamin D more likely? Your lifestyle, medical history, medications, age, and digestive health can all matter.

☐ Would a vitamin D blood test actually be useful for me? That's a conversation to have with your healthcare provider.

Bring this to your provider or pharmacist:

• A list of every supplement you take, with the dose on each label

• Your current medications

• Any symptoms you've noticed, and how long you've had them

The Bottom Line on Vitamin D Deficiency

Vitamin D deserves attention, but it doesn't need hype.

Our bodies need it. Many of us spend most of our days indoors. Night-shift workers and people with limited sun exposure may have fewer opportunities for vitamin D production from sunlight, and relatively few foods naturally contain significant amounts.[1]

But the solution isn't to assume every unexplained symptom is a vitamin D deficiency symptom, order unnecessary testing, or take the highest-dose supplement you can find.

Start with the basics.

Look at your lifestyle.

Look at your diet.

Look at what you're already taking.

Know your risk factors.

And when testing or supplementation makes sense, make that decision with appropriate guidance.

At Wellness Compounding Pharmacy in Cary, NC, we believe supplements should come with the same thing medications should come with: a conversation.

If you're wondering about vitamin D, vitamin D supplements, cod liver oil, or how your current supplements fit together, bring your supplement bottles to the pharmacy, or text us photos of the labels, and we'll go through them together.

Wellness Compounding Pharmacy 218 Towne Village Dr, Cary, NC 27513 (919) 694-5357 info@carywellnessrx.com

This article is for educational purposes and is not intended to diagnose, treat, cure, or prevent any disease. Individual testing and supplement needs vary. Talk with your healthcare provider or pharmacist before starting or changing a supplement, especially if you are pregnant, have a medical condition, or take prescription medications.

Sources

1. NIH Office of Dietary Supplements, Vitamin D fact sheet: https://ods.od.nih.gov/factsheets/VitaminD-Consumer/

2. MedlinePlus, Vitamin D: https://medlineplus.gov/vitamind.html

3. [Add PubMed link for the shift-worker vitamin D study]

4. Demay MB, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024.