Vitamin D Deficiency: 7 Signs You’re Not Getting Enough

You’ve been tired for months. Not “bad night’s sleep” tired — the kind that’s still there after eight hours, the kind that makes your joints ache a little and your patience wear thin faster than it used to. You’ve been blaming stress. Maybe age. Maybe the job.

Here’s something most people never check: there’s a deficiency so widespread it affects over a billion people worldwide — and it mimics almost every symptom of burnout, depression, and chronic fatigue. Most people who have it have no idea they have it.

The result is a quiet deficiency that doesn’t announce itself like an injury. It accumulates. And it shows up in ways most people don’t connect to a vitamin.

Here are the seven signs worth paying attention to.

1. Fatigue That Doesn’t Track With Your Sleep

This is the most common — and most dismissed — symptom. You’re sleeping enough. You don’t have obvious reasons to be tired. But you’re dragging. Not crashed, just consistently behind yourself.

Vitamin D receptors exist throughout the body’s energy-producing systems. When levels drop, mitochondrial function in muscle tissue decreases — measurably. Research published in the North American Journal of Medical Sciences found that vitamin D deficiency was significantly associated with fatigue in otherwise healthy adults, with fatigue scores improving substantially after supplementation.

The catch: fatigue is a symptom of a hundred things, which is why this one gets missed. But if you’re consistently tired without a clear reason, vitamin D is worth checking before you start blaming your sleep habits.

2. Bone Pain and Achiness

Vitamin D is essential for calcium absorption and bone mineralization. Without enough of it, bones can become less dense and more prone to aching — a condition called osteomalacia in adults, which presents as diffuse bone pain rather than joint pain.

Many people describe this as a general achiness they attribute to aging, stress, or sitting too much. And they’re not wrong that those things contribute. But if the achiness is in your bones — particularly in the lower back, hips, and legs — rather than your joints and muscles, vitamin D deficiency is on the differential.

This matters more as you age. Bone density loss is already a feature of aging. Adding vitamin D deficiency to the mix accelerates it in ways that have long-term consequences — consequences that are harder to reverse once bone loss is significant.

3. Getting Sick More Often Than You Should

Vitamin D plays a direct role in immune function. It doesn’t just support the immune system — it actively modulates it, influencing both the innate immune response (your first line of defense) and the adaptive immune response (the targeted, pathogen-specific response).

A landmark meta-analysis in the BMJ examined 25 randomized controlled trials involving over 11,000 participants. Daily or weekly vitamin D supplementation reduced the risk of acute respiratory tract infections — colds, flu, respiratory illnesses — by 12% overall. In people who were severely deficient, the reduction was 70%.

If you’re getting sick more often than your colleagues, your partner, your kids’ classmates — and your lifestyle is otherwise reasonably healthy — your immune system may be running on low vitamin D.

4. Low Mood, Especially in Winter

Seasonal affective disorder is real. What’s less appreciated is that part of its mechanism involves vitamin D.

The brain has vitamin D receptors in regions that regulate mood — including the hypothalamus, which controls circadian rhythms, and areas involved in serotonin synthesis. Low vitamin D is associated with lower serotonin levels, particularly in the months when sunlight exposure drops.

This doesn’t mean vitamin D cures depression. The research is nuanced: supplementation helps more in people who are actually deficient, and the effect is strongest in seasonal patterns. But if your mood reliably worsens in fall and winter, and sunlight exposure reliably lifts it, vitamin D is part of what’s happening — and worth measuring.

5. Slow Wound Healing

Vitamin D regulates the production of growth factors involved in tissue repair. It also modulates inflammation — which matters because healing requires an initial inflammatory response, followed by a resolution phase. When vitamin D is low, this resolution phase can be impaired, slowing healing.

This one often goes unnoticed unless you’re paying attention. Cuts that take longer to heal than they used to. Skin irritation that lingers. Post-workout soreness that doesn’t resolve on the expected timeline.

Slow healing is a late-stage signal — it shows up when deficiency has been present for a while, not in the early stages. If this sounds familiar, the deficiency has likely been building for longer than you realized.

6. Hair Loss

Vitamin D receptors in hair follicles play a role in regulating the hair growth cycle. Alopecia areata — an autoimmune condition causing patchy hair loss — has been associated with low vitamin D levels in multiple studies, with some research suggesting that low vitamin D may contribute to disrupted follicle cycling more broadly.

This is less established than the fatigue and immune findings, and the direction of causation is still being studied. But if you’re experiencing hair thinning or loss that doesn’t have an obvious cause — thyroid function has been checked, stress is manageable, nutritional status is otherwise good — vitamin D is on the list of things to evaluate.

7. Muscle Weakness or Unexplained Aches

Separate from bone pain: muscle weakness and myalgia — generalized muscle aching — are documented symptoms of vitamin D deficiency. Vitamin D receptors exist in skeletal muscle tissue and are involved in protein synthesis and muscle function.

Athletes and active people often notice this as reduced performance, slower recovery, or a muscle “heaviness” that doesn’t track with training load. People who aren’t exercising regularly may notice it as weakness — trouble with stairs, fatigue after carrying groceries, feeling weaker than they’d expect.

This symptom is particularly worth noting because statin medications, which many people in their 30s and 40s are now taking, can cause muscle symptoms — and research suggests that vitamin D deficiency may amplify statin-related myopathy. If you’re on statins and experiencing muscle aches, getting your vitamin D tested is one of the first steps.

What to Actually Do About It

The diagnosis is simple: a standard blood test measures 25-hydroxyvitamin D. Most labs define deficiency as below 20 ng/mL. Insufficiency typically runs between 20-30 ng/mL. Optimal is debated, but most evidence clusters around 40-60 ng/mL as the range associated with the benefits described above.

Sunlight is the most efficient source, but reliable sun exposure is hard to predict and hard to control. Fatty fish (salmon, mackerel, sardines) contain meaningful amounts. Fortified foods (milk, orange juice, some cereals) contribute modestly. Supplementation is where most people with actual deficiency need to go.

For supplementation: vitamin D3 (cholecalciferol) is better absorbed than D2. Doses of 1,000-2,000 IU daily are what most guidelines recommend for maintenance. For correcting significant deficiency, higher doses are sometimes used under medical guidance.

The good news: vitamin D deficiency is among the most correctable nutrient gaps. Get the test. Know your number. Go from there.

References

• Holick MF. “Vitamin D Deficiency.” New England Journal of Medicine, 2007.
• Martineau AR et al. “Vitamin D supplementation to prevent acute respiratory tract infections.” BMJ, 2017.
• Anglin RES et al. “Vitamin D deficiency and depression in adults: systematic review and meta-analysis.” British Journal of Psychiatry, 2013.
• Umar M et al. “Role of Vitamin D Beyond the Skeletal Function.” Nutrients, 2018.
• Lappe JM, Heaney RP. “Why randomized controlled trials of calcium and vitamin D sometimes fail.” Dermato-Endocrinology, 2012.

If you’re in crisis: 988 (US) or your local equivalent. We’ll be here.