Most “14 signs of vitamin D deficiency” lists are padded. The National Institutes of Health names a short set of established signs — bone pain, muscle weakness, soft or deformed bones, fractures — and is explicit that many popular ones (hair loss, sweaty head, weight gain) have no evidence behind them. Low vitamin D is common, but it usually announces itself through a blood test, not a symptom checklist.
This guide separates the signs the NIH actually recognizes from the ones that circulate online, then covers who is at risk, when a test makes sense, and how to fix a low level with food, sun and supplements — including how much is too much.
Key takeaways. Established signs: bone pain, muscle weakness or aches, soft or deformed bones, fractures. Fatigue and low mood are commonly reported but not confirmed by the NIH. A blood level under 30 nmol/L (12 ng/mL) is deficient; 50 nmol/L (20 ng/mL) or above is adequate. Adults need 600 IU a day (800 IU after 70); the safe upper limit is 4,000 IU. If you have symptoms or a risk factor, ask for a 25(OH)D test rather than guessing.
Signs of vitamin D deficiency the NIH recognizes
The NIH Office of Dietary Supplements ties deficiency to two conditions. In children it “causes rickets, a disease in which the bones become soft, weak, deformed, and painful.” In teens and adults it “causes osteomalacia, a disorder that causes bone pain and muscle weakness.” The professional fact sheet adds that signs of osteomalacia “include bone deformities and pain, hypocalcemic seizures, tetanic spasms, and dental abnormalities,” and that “without sufficient vitamin D, bones can become thin, brittle, or misshapen.”
MedlinePlus lists the symptoms that prompt a doctor to order a test: bone pain, muscle weakness or aches, soft or deformed bones, and weak bones and fractures. Longer-term, deficiency “can lead to a loss of bone density, which can contribute to osteoporosis and fractures.”
| Sign | Status | Source |
|---|---|---|
| Bone pain, especially hips, pelvis, legs, ribs | Established | NIH ODS, MedlinePlus |
| Muscle weakness or aches | Established | NIH ODS, MedlinePlus |
| Soft, deformed or bowed bones (rickets in children) | Established | NIH ODS, MedlinePlus |
| Fractures, low bone density | Established | MedlinePlus |
| Muscle spasms, dental abnormalities (severe osteomalacia) | Established, severe cases | NIH ODS |
| Fatigue | Commonly reported, not NIH-confirmed | Cleveland Clinic |
| Mood changes, low mood | Commonly reported, not NIH-confirmed | Cleveland Clinic |
| Muscle cramps | Commonly reported, not NIH-confirmed | Cleveland Clinic |
| Hair loss, sweaty head, weight gain, slow wound healing, frequent colds, back pain | No NIH support | — |
The “weird symptoms” that are not on the list
Fatigue and low mood are the most common complaints attached to low vitamin D online. The Cleveland Clinic does list “fatigue,” “muscle weakness, muscle aches or muscle cramps” and “mood changes, like depression” among possible adult symptoms — but it also notes that “you may have no signs or symptoms of vitamin D deficiency.” The NIH goes a step further on mood: “clinical trials show that taking vitamin D supplements does not prevent or ease symptoms of depression.” Low mood may travel with low vitamin D; fixing the vitamin has not been shown to fix the mood.
Hair loss, a sweaty head, weight gain, slow-healing wounds, back pain specifically, and “getting sick all the time” do not appear on any NIH or MedlinePlus page about deficiency. They may have other causes worth checking; treating them as vitamin D signs mostly sells supplements.
Who is at risk
The NIH names six groups: “breastfed infants, older adults, people with limited sun exposure, people with dark skin, people with conditions that limit fat absorption, and people with obesity.” The reasons, from the consumer sheet:
- Breastfed infants. “Breast milk alone does not provide infants with an adequate amount of vitamin D.” Infants need 400 IU a day, usually as drops.
- Older adults. “As you age, your skin’s ability to make vitamin D when exposed to sunlight declines.”
- Little sun. People “who do not go outside or because they keep their body and head covered” — office workers in winter count.
- Dark skin. “The darker your skin, the less vitamin D you make from sunlight exposure.”
- Fat malabsorption. “Crohn’s disease, celiac disease, or ulcerative colitis,” plus some liver disease and cystic fibrosis.
- Obesity or gastric bypass. Fat tissue holds vitamin D away from the blood; these groups “may need more vitamin D than other people.”
How common is it? In NHANES 2011–2014 data cited by the NIH, “18% were at risk of inadequacy … and 5% were at risk of deficiency.” Risk was uneven: “17.5% of non-Hispanic Blacks were at risk of vitamin D deficiency, as were 7.6% of non-Hispanic Asians, 5.9% of Hispanics, and 2.1% of non-Hispanic White people.” The widely quoted “42% of Americans are deficient” uses a higher cutoff and is not the NIH figure.
Testing: what the numbers mean
The test is a blood measurement of 25-hydroxyvitamin D, written 25(OH)D. MedlinePlus: “The test is usually done if your health care provider thinks that a bone or other health condition you have could be caused by very low vitamin D levels.” For people with no symptoms and no risk factor, the U.S. Preventive Services Task Force found “the current evidence is insufficient to assess the balance of benefits and harms of screening” — so routine testing of healthy adults is not recommended, but testing when there is a reason is.
| 25(OH)D level | NIH interpretation |
|---|---|
| Below 30 nmol/L (12 ng/mL) | Deficient — can lead to rickets or osteomalacia |
| 30 to below 50 nmol/L (12–20 ng/mL) | Generally inadequate for bone and overall health |
| 50 nmol/L (20 ng/mL) and above | Generally adequate for bone and overall health |
| Above 125 nmol/L (50 ng/mL) | Linked to potential adverse effects, particularly above 150 nmol/L (60 ng/mL) |
Cutoffs from the NIH ODS professional fact sheet. Labs report in either unit; 2.5 nmol/L = 1 ng/mL.
How much you need
The NIH recommended intakes: 400 IU (10 mcg) from birth to 12 months, 600 IU (15 mcg) from age 1 through 70, and 800 IU (20 mcg) after 70. The upper limit — the most you should take daily without medical supervision — is 4,000 IU (100 mcg) from age 9 up, lower for younger children: 1,000 IU under 6 months, 1,500 IU at 7–12 months, 2,500 IU at 1–3 years, 3,000 IU at 4–8. Someone with a confirmed deficiency may be prescribed more for a limited period; that is a clinician’s call, not a default.
Fixing a low level: food, sun, supplements
Food
Few foods carry much vitamin D naturally; fatty fish and fortified dairy do most of the work. Per serving, from the NIH table:
| Food | Serving | Vitamin D |
|---|---|---|
| Cod liver oil | 1 tablespoon | 1,360 IU |
| Rainbow trout, farmed, cooked | 3 oz | 645 IU |
| Sockeye salmon, cooked | 3 oz | 570 IU |
| White mushrooms, UV-exposed, raw | ½ cup | 366 IU |
| Milk, 2%, fortified | 1 cup | 120 IU |
| Fortified breakfast cereal | 1 serving | 80 IU |
| Sardines, canned in oil | 2 sardines | 46 IU |
| Egg, scrambled | 1 large | 44 IU |
| Tuna, light, canned in water | 3 oz | 40 IU |
| Cheddar cheese | 1.5 oz | 17 IU |
Two servings of fatty fish a week plus fortified milk gets many people to the RDA; eggs and cheese alone do not. Only UV-exposed mushrooms count — ordinary ones carry little. Because vitamin D is fat-soluble, the NIH notes it “is best absorbed when taken with a meal or snack that includes some fat.” Our vitamin D–rich foods guide has more options.
Sun
The NIH describes what usually works: “approximately 5 to 30 minutes of sun exposure, particularly between 10 a.m. and 4 p.m., either daily or at least twice a week to the face, arms, hands, and legs without sunscreen.” Two caveats follow immediately. “Sunscreens with an SPF of 8 or more appear to block vitamin D-producing UV rays,” and “UV radiation is a carcinogen, and UV exposure is the most preventable cause of skin cancer” — which is why the NIH calls limiting exposure “prudent” rather than prescribing sun time. In northern states from roughly November to February, and for people with dark skin or who cover up, sun is not a reliable source. You “cannot get too much vitamin D from sun exposure,” per MedlinePlus — the skin limits production.
Supplements
Two forms exist. The NIH: “Both forms increase vitamin D in your blood, but D3 might raise it higher and for longer than D2.” Either works; D3 is the common choice. Take it with a meal that contains fat. For a confirmed deficiency, MedlinePlus is direct: “the treatment is with supplements” — food and sun rarely correct a level that is already low.
Check interactions. Per the NIH, orlistat “can reduce the amount of vitamin D your body absorbs,” statins “might not work as well if you take high-dose vitamin D supplements,” steroids such as prednisone “can lower your blood levels of vitamin D,” and thiazide diuretics “could raise your blood calcium level too high if you take vitamin D supplements.” If you are on any of these, dose with your clinician.
Too much is a real risk — from supplements only. The NIH: very high blood levels “can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones.” That comes from high-dose supplements over time, not from food or sun. Stay at or under 4,000 IU a day unless a clinician has prescribed more and is checking your blood.
What we are not claiming
- That fatigue, hair loss, low mood or frequent colds mean you are low in vitamin D. None is an NIH-recognized sign; fatigue and mood are consumer-level reports from the Cleveland Clinic only.
- That vitamin D supplements treat depression, prevent cancer, multiple sclerosis or COVID-19. The NIH’s trial summaries say no for depression and cancer incidence, “no firm consensus” for MS, and “insufficient” evidence for COVID-19.
- That everyone should be screened. The USPSTF found insufficient evidence for screening adults without symptoms.
- That D2 is useless. The NIH says both forms raise blood levels; D3 does so somewhat more.
FAQs
What are the first signs of vitamin D deficiency?
Often none. When signs appear, the NIH-recognized ones are bone pain and muscle weakness; in children, soft or bowed bones. Fatigue and low mood are commonly reported but not confirmed.
Can vitamin D deficiency cause hair loss?
No NIH or MedlinePlus page lists hair loss as a sign of deficiency. Hair loss has many causes worth checking with a clinician; vitamin D is not an established one.
How do I know if I am low in vitamin D?
Only a 25(OH)D blood test tells you. Below 30 nmol/L (12 ng/mL) is deficient; 50 nmol/L (20 ng/mL) or above is adequate. Ask for it if you have bone pain, muscle weakness or a risk factor.
How much vitamin D should I take a day?
600 IU for ages 1–70 and 800 IU after 70, per the NIH. The upper limit for adults is 4,000 IU a day unless prescribed otherwise.
Is vitamin D2 or D3 better?
Both raise blood levels; the NIH notes D3 “might raise it higher and for longer.” D3 is the usual choice.
How long does it take to fix a deficiency?
That depends on the starting level and dose, which is why treatment is set and rechecked by a clinician rather than self-managed. Blood levels respond to daily supplements over weeks to months.
This content is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for personalised guidance.
