4 sneaky signs of vitamin D deficiency that are easy to miss, according to dietitians

Remember when Mom used to stress how important drinking milk is for your bones? Turns out, she was onto something. Fortified milk is not only one of the best ways to get calcium, but it’s also a good source of vitamin D — a nutrient that helps your body absorb that calcium and keep your bones strong.

But vitamin D’s benefits go well beyond the skeletal system. The nutrient also plays a role in brain health and immune function, and it’s important for your muscles, heart and mood. Some research even suggests that maintaining healthy vitamin D levels may be linked to healthy aging and longevity.

So yes, vitamin D does a lot for your body. But how do you know if you’re actually getting enough of this essential nutrient? The best way is by having your levels checked during routine blood work at your annual physical. Blood levels below 30 nanomoles per liter (nmol/L) are generally considered deficient, while levels of 50 nmol/L or higher are considered adequate for most people.

If you don’t have blood work scheduled anytime soon, there are also signs and symptoms to watch for that could indicate your levels are low. Yahoo spoke with five health experts about easy-to-miss signs of vitamin D deficiency, what causes it in the first place — and how to know if you may be at higher risk — plus what to do if your levels need a boost.

Signs of vitamin D deficiency that aren’t always obvious

One of the most obvious — and severe — signs of vitamin D deficiency is frequent bone fractures. But long before that happens, there may be other earlier and less obvious symptoms to watch for.

Just keep in mind that while these signs could indicate you’re not getting enough vitamin D, they can also have many other causes. The best course of action? Make an appointment with your primary care doc to figure out what’s going on.

Muscle and bone pain

Low vitamin D levels can cause muscle weakness, cramps and bone pain. According to Yale Medicine, muscle weakness often affects the upper arms, hips and thighs, which can make walking feel more difficult or unsteady. Muscle spasms, twitches and tremors may also occur.

Frequent illnesses

If it feels like you’re always catching the cold going around the office, it might not just be bad luck — or poor handwashing habits. Vitamin D plays an important role in maintaining a healthy immune system, including interacting with immune cells that help the body fight infections.

That said, simply taking vitamin D supplements isn’t guaranteed to keep illnesses at bay. However, research suggests that being deficient in this nutrient may increase your risk of getting sick.

For example, a 2026 observational study published in The American Journal of Clinical Nutrition analyzing data from more than 36,000 adults in the U.K. Biobank found that people with severe vitamin D deficiency had a 33% higher risk of hospitalization for respiratory tract infections compared with those whose levels were 75 nmol/L or higher. The researchers also found that for every 10 nmol/L increase in vitamin D levels, hospitalization rates for respiratory infections dropped by about 4%.

A separate observational study from Australia found that higher vitamin D intake was associated with a lower frequency of respiratory illnesses.

Depression

According to Wesley Buckle, a licensed naturopathic doctor at the Oasis Addiction Treatment Center, vitamin D isn’t a treatment for depression, but low levels have been linked to mood changes. This may be partly because vitamin D plays a role in regulating neurotransmitters — chemical messengers that help brain cells communicate — and in supporting the health of neurons, the cells involved in processing emotions.

It’s also worth noting that the research on vitamin D supplements and depression is mixed. A 2024 meta-analysis in the Journal of Affective Disorders found that supplementation may help reduce depressive symptoms in certain adults, but the benefits appear to depend on factors like a person’s baseline vitamin D levels and the severity of their depression.

Chronic fatigue

Feeling extra tired? According to registered dietitian Avery Zenker, low vitamin D can leave you feeling flat, foggy and unmotivated. In other words, if you’ve been feeling especially sluggish lately, it may be worth getting your levels checked. The confusing part? “Although you might feel tired, it can actually be harder to sleep,” she says.

Family nurse practitioner Allison Christel, MSN, agrees. “Fatigue is the sneakiest one because it creeps in so gradually that most people just chalk it up to being busy or stressed,” she says. “By the time they notice it, their levels may have been low for months.”

Some research suggests there may be a connection between vitamin D levels and fatigue. In a 2016 randomized placebo-controlled trial of adults with vitamin D deficiency, participants who received a high-dose vitamin D supplement reported greater improvements in fatigue scores than those who received a placebo. More recently, a 2025 observational study found that people with lower vitamin D levels tended to report more severe fatigue. Still, correlation isn’t the same as causation, and other factors could also play a role.

Overall, more research is needed to fully understand the relationship, since fatigue can have many different causes.

Are there any risk factors if vitamin D levels stay low?

Chronically low vitamin D can result in weak bones at any age. In infants and young children, developing bones can become misshapen or deformed, causing rickets, a softening and weakening of bones. For adults, chronically low vitamin D may cause bones to break more easily than usual. Adults may also develop osteoporosis, which can result in a stooped posture.

Long-term vitamin D deficiency can also affect the parathyroid glands, which help regulate calcium levels in the blood. When vitamin D levels are low, the body may produce more parathyroid hormone to maintain calcium balance — a condition known as secondary hyperparathyroidism. Over time, this can contribute to additional bone loss and muscle weakness.

What causes low vitamin D levels?

Vitamin D isn’t naturally found in many foods (though a few good sources are listed below), which can make it harder to get enough from your diet alone. Instead, most of your vitamin D is produced when your skin is exposed to sunlight. That means one of the most common reasons for low vitamin D levels is simply not getting enough exposure to the sun’s UVB rays. Spending less time outdoors or regularly wearing protective clothing that covers most of your skin can reduce the amount of vitamin D your body makes, says Katherine Zeratsky, a registered dietitian at the Mayo Clinic.

It can feel like a bit of a balancing act: You want to protect your skin from harmful UV rays, but you also need some sun exposure to help your body produce vitamin D. The good news is that even brief time outdoors can help. Just a few minutes of sun exposure several times a week may support vitamin D production for some people, though needs vary depending on factors like skin tone, location and season. And wearing sunscreen — which dermatologists recommend to reduce skin cancer risk — doesn’t appear to significantly interfere with vitamin D production in real-world conditions.

If you’d still rather limit sun exposure, there are other ways to get vitamin D, including fortified foods and supplements.

In some cases, underlying health conditions may also contribute to low vitamin D levels. According to Zeratsky, conditions that affect fat absorption — such as celiac disease or Crohn’s disease — as well as kidney disease, can make it harder for the body to process vitamin D. Certain medications may also lower vitamin D levels, including some steroids, weight-loss drugs and medications that affect fat absorption.

Who is most at risk for low vitamin D?

Anyone can be deficient in vitamin D, but some people tend to be more affected than others. These include:

• People who spend most of the day indoors. Since vitamin D is primarily produced when your skin is exposed to sunlight, spending little time outside can increase the risk of low levels.

• People who live in northern latitudes. In places farther from the equator, sunlight isn’t strong enough during parts of the year for the skin to produce adequate vitamin D.

• Older adults. Adults over 65 have a higher risk of deficiency, Zeratsky says, because aging skin becomes less efficient at producing vitamin D when exposed to sunlight.

• People with darker skin. Higher levels of melanin reduce the skin’s ability to produce vitamin D from sunlight, which can increase the risk of deficiency.

• Breastfed infants or babies who drink less than 32 ounces of infant formula per day. The American Academy of Pediatrics recommends that these infants receive 400 IU of vitamin D daily (using an infant formulation), or as directed by a pediatrician.

How much vitamin D do you need?

The amount of vitamin D needed each day varies depending on age. However, the daily recommended dose to sustain vitamin D levels is 10 micrograms (mcg) for infants and 15 mcg for ages 1 through 70. After 71, the daily recommended dose is 20 mcg.

If you suspect that you’re deficient, your doctor can help you determine whether you need to supplement and what your dosage should be. Zeratsky says that your care provider will typically prescribe a higher dose of vitamin D for a specific period to see if it normalizes your levels. After a few months, your levels should be rechecked, and the dosage should be adjusted based on your results.

Can you get too much vitamin D?

While you typically hear about people having a vitamin D deficiency, it’s possible to also have what’s called vitamin D toxicity, meaning you have too much vitamin D in your system. It’s rare and usually caused by high doses of vitamin D supplements rather than sun exposure.

If severe, it can cause a buildup of calcium in your blood and trigger nausea, vomiting, confusion or kidney stones due to high calcium levels, Zeratsky notes.

Vitamin D supplements can also interact with certain medications — including some statins and diuretics.

Unless your health care provider recommends otherwise, it’s best not to exceed the Tolerable Upper Intake Levels (UL) from supplements:

• 0-16 months: 25 mcg (1,000 IU)

• 7-12 months: 38 mcg (1,500 IU)

• 1-3 years: 63 mcg (2,500 IU)

• 4-8 years: 75 mcg (3,000 IU)

• 9 years+: 100 mcg (4,000 IU)

How can you increase your vitamin D levels?

Vitamin D is one of the few nutrients that’s hard to get enough of in the diet unless you eat fish regularly. While it’s still helpful to eat vitamin D-rich foods, for most people, the best way to get enough vitamin D is through sun exposure or supplements — or a combination of both.

Foods

One of the richest dietary sources of vitamin D is cod liver oil, which provides 170% of the Daily Value (DV) per 1 tablespoon-sized serving.

Here are the other top food sources of vitamin D:

Sun exposure

Research suggests that about 5 to 30 minutes of direct sunlight on the skin most days of the week may be enough for many people to produce adequate vitamin D. However, how much vitamin D your body makes from sun exposure depends on several factors — most notably your skin type, latitude and the time of year.

For example, people who live at higher latitudes, like Boston, may not be able to produce enough vitamin D during the fall and winter because sunlight isn’t strong enough for the skin to make it efficiently. People with darker skin may also produce less vitamin D from sunlight, since higher levels of melanin reduce the skin’s ability to synthesize vitamin D.

Supplements

Vitamin D supplements are an easy and effective way to boost your intake. But supplements aren’t all created equal. When shopping for one, look for vitamin D3 (cholecalciferol), the form that tends to raise and maintain vitamin D levels in the blood more effectively than vitamin D2. It’s also a good idea to choose products with minimal additives.

To make sure you’re actually getting what the label promises, look for supplements that have been tested for purity and potency, ideally by a third-party organization, such as NSF, USP or Informed Choice.

As for how much vitamin D to take, that ultimately depends on your current vitamin D levels. People with a severe deficiency may be prescribed high-dose supplements by their health care provider, while someone who’s simply low in vitamin D may benefit from starting with a supplement containing 1,000 IU to 2,000 IU.

To reduce your risk of vitamin D toxicity, follow dosing recommendations and start with a lower amount unless your health care provider advises otherwise.

Registered dietitian Anne Murray, MS, RD, also recommends having your vitamin D levels rechecked every three to six months so your provider can monitor your progress and adjust your dose if needed.

FAQs

Are at-home vitamin D tests reliable?

“At-home tests can be a good starting point for someone who is just curious about their levels,” says Christel. However, at-home testing isn’t a replacement for a comprehensive evaluation by a licensed health care professional. “A lab draw ordered through your provider gives you a more complete picture. Your nurse practitioner or doctor can look at your levels in context with your symptoms, medications and overall health to make a personalized dosing recommendation,” she adds.

Should you take vitamin K2 with vitamin D?

You don’t have to take vitamin K2 with vitamin D, but some experts suggest the two may work well together because both play roles in bone health. Vitamin D helps your body absorb calcium, while vitamin K helps activate proteins that regulate where calcium is used in the body — including in bones and teeth.

That said, most people who eat a balanced diet already get enough vitamin K, and research is still limited on whether taking vitamins K2 and D together provides additional benefits for bone health.

Meet our experts

• Avery Zenker, registered dietitian at MyCrohnsAndColitisTeam

• Wesley Buckle, naturopathic doctor at Oasis Addiction Treatment Center

• Allison Christel, MSN, FNP-C, founder of PlantedRx

• Katherine Zeratsky, registered dietitian at the Mayo Clinic

• Anne Murray, MS, RD

Our health content is for informational purposes only and is not intended as professional medical advice. Consult a medical professional on questions about your health.

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