During cold and flu season, and the COVID-19 pandemic, it is essential to maintain healthy levels of vitamin D to help reduce your risk of viral and bacterial illness.5,6 A blood test is the best way to determine your vitamin D levels, but here are some symptoms that may indicate your levels are low.
1. Aching muscles — Nearly half of all adults are affected by muscle pain.7 Researchers believe most of those are deficient in vitamin D. Some studies have suggested that nerves have vitamin D receptors that affect the perception of pain. In one animal model, research demonstrated a vitamin D-deficient diet can induce deep muscle hypersensitivity that was not connected to low levels of calcium.8
2. Painful bones — Vitamin D regulates the level of calcium in your body, necessary to protect bone health.9 Vitamin D deficiency can cause your bones to soften, called osteomalacia. This may be a precursor to osteoporosis.
3. Fatigue — This is a common symptom of a variety of different health conditions, including sleep deprivation. Researchers have found that supplementing cancer patients suffering from fatigue can improve their symptoms.10 In one study11 using 174 adults with fatigue and stable medical conditions, the researchers found 77.2% were deficient in vitamin D. After normalizing their level, the fatigue symptoms improved significantly.
4. Reduced muscle performance — Vitamin D deficiency is as common in athletes as in others. Vitamin D is crucial for muscle development, strength and performance. Older adults taking a vitamin D supplement have a reduced risk of falls and improved muscle performance.12
Correction through oral supplementation or sensible sun exposure may reduce symptoms of stress fractures, musculoskeletal pain and frequent illness. Vitamin D also has a direct effect on muscle performance. In one paper from the Journal of the American Academy of Orthopaedic Surgeons, the author wrote:13 “Higher serum levels of vitamin D are associated with reduced injury rates and improved sports performance. In a subset of the population, vitamin D appears to play a role in muscle strength, injury prevention, and sports performance.”
5. Brain health — Vitamin D is also essential for your brain health. Symptoms of deficiency can include dementia caused by an increase of soluble and insoluble beta-amyloid, a factor in Alzheimer's disease.14 Research has also found an association with depression15 that may be associated with the function of vitamin D buffering higher levels of calcium in the brain.16
Vitamin D deficiency in pregnant women can increase the risk of autism and schizophrenic-like disorders in the baby.17 One study of people with fibromyalgia found a vitamin D deficiency was more common in those who had anxiety and depression.18 Another looked at vitamin D deficiency in obese subjects and found a relationship between low levels of vitamin D and depression.19
6. Poor sleep — The mechanism linking vitamin D and poor sleep quality has not been identified. But research has found people with low levels of vitamin D have poor quality sleep and a higher risk of sleep disorders.20
7. Sweaty head — Excessive sweating, especially on your head, or a change in your pattern of sweating, can indicate a vitamin D deficiency.21
8. Hair loss — Vitamin D is crucial to the proliferation of keratinocytes and plays an important role in your hair cycle. The vitamin D receptor appears to play a role in the anagen phase of hair growth, leading researchers to conclude, "Treatments that upregulate the vitamin D receptor may be successful in treating hair disorders and are a potential area of further study."22
9. Slow-healing wounds — Chronic wounds are a major public health challenge.23 In the U.S. 2% of the population is affected by chronic wounds and it is estimated to account for 5.5% of the cost of health care in the U.K. NHS. Vitamin D promotes wound healing and the creation of cathelicidin, a peptide that fights wound infections.24
10. Dizziness — Evidence from animal models suggests that vitamin D is critical in the development of the inner ear,25 which affects balance and coordination. Analysis of people with vestibular neuritis, characterized by vertigo, showed lower serum vitamin D levels than in people without vestibular neuritis.26
11. Heart problems — Clinical studies have shown that vitamin D3 improves circulation and can help improve high blood pressure.27 In one study28 researchers discovered that vitamin D3 also has a significant effect on the endothelial cells that line your cardio-vascular system. They found that it helped balance concentrations of nitric oxide and peroxynitrite, which improved endothelial function.
12. Excess weight — How vitamin D affects obesity has not been identified. However, data does show there is a high probability of deficiency in people who are obese.29
13. Recurring infections — There have been multiple epidemiological studies that show vitamin D deficiency can increase the risk of infection and raise the severity, particularly in respiratory tract infections.30 Multiple studies have demonstrated that vitamin D deficiency increases the potential risk for severe disease and mortality, especially in those who are critically ill.31
14. Reduced cognitive function — Data shows that vitamin D deficiency increases your risk of dementia twofold32 and raises your risk of impaired cognitive function.33