Vitamin D Deficiency: Signs, Risk Factors, and What to Do Next

When tiredness lingers, it is tempting to pin the feeling on one nutrient and order a giant bottle of supplements. Vitamin D deficiency deserves a more careful approach. It may cause no obvious symptoms, but severe or prolonged deficiency can weaken bones and muscles. A blood test—not a symptom checklist—is the clearest way to know where you stand.

Vitamin D matters deeply, but more is not always better; the kindest next step is good information, an appropriate test, and a plan that fits the person.

What vitamin D deficiency can feel like

Vitamin D helps the body absorb calcium and supports bone, muscle, nerve, and immune function. In adults, a significant deficiency can lead to osteomalacia, a softening of the bones that may cause bone pain and muscle weakness. In children, severe deficiency can cause rickets.

Milder low levels often do not announce themselves clearly. Fatigue, aches, or low mood have many possible causes, so those symptoms cannot diagnose vitamin D deficiency on their own. This is important: a broad wellness checklist may feel convincing while pointing you away from the actual reason you feel unwell.

See a clinician if you have persistent symptoms, bone pain, significant muscle weakness, repeated fractures, or risk factors for deficiency. This guide is educational and cannot replace personal medical care.

Who is more likely to have low vitamin D?

The body can make vitamin D when bare skin is exposed to sunlight, but the amount varies with season, latitude, time of day, cloud cover, sunscreen use, skin pigmentation, age, and how much skin is exposed. That is why “just get more sun” is not a precise or universally safe prescription.

Risk is higher for older adults, people with limited sun exposure, people with darker skin, and those whose digestive conditions reduce fat absorption. Obesity and gastric bypass surgery can also affect vitamin D status. Breastfed infants need a clinician-guided vitamin D plan because human milk alone usually does not provide enough.

• Limited regular exposure to sunlight
• Darker skin pigmentation
• Older age
• Conditions such as celiac disease, Crohn’s disease, or ulcerative colitis that can impair absorption
• Obesity or previous gastric bypass surgery
• Medicines that affect vitamin D metabolism

How testing and blood levels are interpreted

The usual blood test measures 25-hydroxyvitamin D, written as 25(OH)D. According to the National Institutes of Health, levels of 20 nanograms per milliliter or above are adequate for most people’s bone and overall health, while levels below 12 nanograms per milliliter are too low. Results between those points need context, and professional groups do not agree on one ideal number for everyone.

Testing is not automatically needed for every healthy person. A clinician may recommend it when symptoms, medical history, medication use, or risk factors make the result useful. They can also interpret the laboratory’s units and reference range, which prevents an isolated number from causing unnecessary alarm.

If a deficiency is confirmed, treatment may require a higher short-term dose than routine daily needs. That should be planned and monitored by a qualified professional rather than copied from someone else’s regimen.

Food, supplements, and safe next steps

Few foods naturally contain much vitamin D. Fatty fish such as salmon, trout, tuna, and mackerel are among the strongest sources. Egg yolks, cheese, and beef liver contain smaller amounts, and some mushrooms exposed to ultraviolet light provide vitamin D. In the United States, many milks and plant-based beverages are fortified, so the nutrition label is your best guide.

For adults ages 19 to 70, the recommended amount is 15 micrograms (600 IU) daily; adults 71 and older need 20 micrograms (800 IU). The adult upper limit is 100 micrograms (4,000 IU) per day unless a healthcare professional uses a different dose to treat a diagnosed problem. Too much supplemental vitamin D can cause harmful calcium buildup and other serious effects.

Begin with what you know: review food labels, consider whether you have meaningful risk factors, and ask whether testing would change your care. You can also see how eggs fit into the picture in our guide to protein in an egg. The goal is not the biggest supplement dose; it is a safe, evidence-based path back to an adequate level.

Sources

• National Institutes of Health Office of Dietary Supplements: Vitamin D Fact Sheet for Consumers
• MedlinePlus: Vitamin D Deficiency
• Centers for Disease Control and Prevention: Vitamin D and Iron for Infants