Vitamin D is unusual among nutrients because your body can make its own supply from sun exposure on skin, yet deficiency remains remarkably common. The National Institutes of Health Office of Dietary Supplements estimates that a significant share of the population has insufficient vitamin D levels, driven by limited sun exposure, darker skin (which produces less vitamin D from the same sun exposure), higher body weight, aging skin, and geography.
Because vitamin D plays a role in calcium absorption, immune function, muscle strength, and mood regulation, deficiency symptoms can be subtle at first and easy to write off as stress or normal aging. According to Mayo Clinic, symptoms often develop gradually and are frequently mistaken for other conditions until a blood test reveals low levels.
Here are 12 signs that may point to low vitamin D, along with who’s most at risk and how to address it.
1. Persistent Fatigue
Feeling tired despite adequate sleep is one of the most commonly reported symptoms of low vitamin D, likely tied to its role in cellular energy production and inflammation regulation.
2. Bone and Back Pain
Vitamin D is essential for calcium absorption, so chronically low levels can lead to weaker bones and a dull, persistent ache in the lower back and joints.
3. Muscle Weakness or Aches
Vitamin D receptors are present in muscle tissue, and deficiency has been linked to reduced muscle strength and generalized aching, particularly in older adults.
4. Frequent Illness or Infections
Vitamin D plays an important role in immune function, and low levels have been associated with more frequent colds, respiratory infections, and slower recovery.
5. Low Mood or Symptoms of Depression
Vitamin D receptors are present in areas of the brain involved in mood regulation, and some research has found associations between low vitamin D and depressive symptoms, particularly during darker winter months.
6. Slow Wound Healing
Vitamin D supports the skin’s inflammatory response during healing, and some research suggests deficiency may slow recovery after surgery or injury.
7. Hair Loss
Vitamin D plays a role in the hair growth cycle, and significant deficiency has been linked to hair thinning and, in more severe cases, alopecia.
8. Bone Loss and Increased Fracture Risk
Long-term deficiency can contribute to decreased bone mineral density over time, raising the risk of fractures, especially in postmenopausal women and older adults.
9. Getting Sick More Often Than Usual
Beyond frequent colds, some research links very low vitamin D levels to a higher risk of more serious respiratory infections, underscoring its broader immune role.
10. Impaired Cognitive Function
In older adults, low vitamin D levels have been associated with poorer performance on cognitive tests, though researchers are still working out how much of this is cause versus correlation.
11. Sweaty Scalp or Excess Sweating
Some clinicians note unexplained scalp sweating as an early, if nonspecific, symptom historically associated with vitamin D deficiency, particularly in infants.
12. Bone Pain in Children (Rickets)
In children, severe, prolonged vitamin D deficiency can cause rickets, a condition marked by soft, weak bones and skeletal deformities, though this is less common where fortified foods are widely available.
Who’s Most at Risk
- People with limited sun exposure: those who work indoors, live in northern latitudes, or consistently wear sunscreen and protective clothing.
- People with darker skin: higher melanin content reduces the skin’s vitamin D production from the same amount of sun exposure.
- Older adults: aging skin is less efficient at producing vitamin D from sunlight.
- People with obesity: vitamin D is fat-soluble and can be sequestered in body fat, reducing its circulating availability.
- People with malabsorption conditions: Crohn’s disease, celiac disease, and gastric bypass surgery can all impair vitamin D absorption.
Food Sources and Sun Exposure
Fatty fish like salmon and mackerel, egg yolks, fortified milk and plant milks, fortified cereals, and mushrooms exposed to UV light all contribute dietary vitamin D, though few foods naturally contain large amounts. Brief, unprotected sun exposure (roughly 10 to 30 minutes a few times a week, depending on skin tone and location) allows the body to synthesize its own supply, though this must be balanced against skin cancer risk.
When to See a Doctor
A simple blood test, the 25-hydroxyvitamin D test, can confirm whether your levels are low. If you’re experiencing several of the symptoms above, particularly persistent fatigue, bone pain, or frequent illness, it’s worth discussing testing with your doctor rather than guessing based on symptoms alone, since many of these signs overlap with other conditions.
The Bottom Line
Vitamin D deficiency is common, often subtle, and easy to mistake for other issues like stress or normal aging. If several of these signs sound familiar, a blood test is the most reliable way to know for sure, and correcting a deficiency through diet, supplementation, or sensible sun exposure is usually straightforward once identified.
This article is for informational purposes only and is not a substitute for professional medical advice. Always talk to a doctor before starting vitamin D supplementation, since excessive intake can also cause health problems.
