Vitamin D deficiency: what it feels like, who’s at risk, and when to test

Symptoms like bone or muscle pain and lingering fatigue can have many causes, including low vitamin D. Because the signs are often vague, it helps to know what’s typical of deficiency, which blood test actually measures vitamin D status, and what results mean. This page walks you through the symptoms doctors look for, the groups most likely to be low, when testing is useful, and how to act on the numbers safely.

What vitamin D deficiency can feel like

In adults, severe deficiency can soften bone (osteomalacia), which commonly causes bone pain and muscle weakness; both are classic symptoms your clinician will ask about, according to the National Institutes of Health’s Office of Dietary Supplements (NIH ODS consumer fact sheet). Other day‑to‑day complaints like fatigue are reported too, but they’re not specific to vitamin D and can come from many conditions.

If you’re sorting through overlapping symptoms, our guide on making sense of common symptoms can help you decide what to track and when to see a clinician.

Who is more likely to have low vitamin D?

Some groups are more likely than others to have inadequate vitamin D. NIH ODS lists breastfed infants, older adults, people with limited sun exposure, people with dark skin, those with conditions that limit fat absorption (such as celiac or Crohn’s disease), and people with obesity or after gastric bypass among higher‑risk groups (NIH ODS health professional fact sheet).

Which test checks your vitamin D — and when is it useful?

The lab test that reflects vitamin D stores is serum 25‑hydroxyvitamin D [25(OH)D]; the active hormone (1,25‑dihydroxyvitamin D) is not a good status marker and usually stays normal until deficiency is severe. CDC materials likewise list 25‑hydroxyvitamin D among nutrition biomarkers that may be measured in health care settings (CDC).

For people without symptoms, the U.S. Preventive Services Task Force concluded in April 2021 that evidence is insufficient to recommend for or against screening adults for vitamin D deficiency (USPSTF recommendation). The Endocrine Society’s 2024 guideline also does not recommend routine 25(OH)D testing in generally healthy people and notes that fixed “sufficient” thresholds are not supported by trial data (Endocrine Society guideline; companion commentary in JCEM: Endocrine Society communication).

Testing is more likely to help if you have symptoms compatible with deficiency, risk factors for low levels, or a condition where knowing your level would change care (for example, certain bone, kidney, or malabsorption disorders). Your clinician can order the 25(OH)D test and consider it alongside calcium, parathyroid hormone, and your exam.

What do vitamin D numbers mean?

NIH’s Food and Nutrition Board classifies 25(OH)D concentrations this way for most healthy people: less than 12 ng/mL (30 nmol/L) is associated with deficiency, 12–19 ng/mL (30–49 nmol/L) is generally inadequate, and 20 ng/mL (50 nmol/L) or higher is generally adequate for bone and overall health; very high levels above about 50–60 ng/mL (125–150 nmol/L) have been linked to adverse effects. Keep in mind, assay methods vary between labs, so a single result can read a bit higher or lower depending on where it’s measured.

Symptoms by severity

• Mild to moderate low levels: often no symptoms, or nonspecific complaints like fatigue or muscle aches that overlap with many other conditions.
• More severe deficiency: bone pain and proximal muscle weakness from osteomalacia are typical in adults.

What can you do if your level is low?

• Confirm the pattern: Your clinician may repeat or standardize the 25(OH)D test if the number doesn’t match your history and exam because laboratory methods differ.
• Address intake and absorption: Getting vitamin D from fortified foods and safe sun exposure helps, but people in at‑risk groups often need supplements to reach adequate status.
• Use supplements thoughtfully: The Endocrine Society’s 2024 guideline advises that most healthy adults under 75 do not benefit from taking more than the recommended daily allowance and generally do not need testing unless there’s a specific indication (Endocrine Society news release).

Safety: watch for too much of a good thing

Vitamin D toxicity is rare but typically results from excessive supplement intake. It leads to high calcium (hypercalcemia) with symptoms such as nausea, vomiting, thirst, frequent urination, muscle weakness, and in severe cases kidney injury; blood 25(OH)D levels in toxicity are often above 150 ng/mL (375 nmol/L).

How to put this into practice

• Track symptoms that fit deficiency (bone pain, muscle weakness) alongside risk factors like limited sun or malabsorption. Note what makes them better or worse.
• If you and your clinician decide to test, ask for the 25‑hydroxyvitamin D test and keep a copy of the result for comparison later.
• If your level is low and symptoms fit, discuss a plan that may include supplements, diet changes, and checking calcium. Routine screening without symptoms isn’t supported by current evidence.

How to know if things are improving

• Symptom check: Bone pain and muscle weakness from osteomalacia should ease as vitamin D status and calcium balance normalize, though timelines vary.
• Lab follow‑up: Your clinician may recheck 25(OH)D — ideally using the same lab — to confirm you’ve reached an adequate range for bone health while avoiding very high levels linked with harm.
• Big picture: Many common symptoms like low energy have multiple causes. If fatigue persists despite normal vitamin D, consider other explanations with your clinician; our read on why you might always feel tired can help you prepare questions for that visit.