Vitamin D deficiency is remarkably common, affecting close to a billion people worldwide, yet it often goes unnoticed because the symptoms are easy to mistake for everyday tiredness or stress. Here is a clear guide to the signs your body may be sending, why they happen, and what to do about them.
The Short Answer
The most common signs of vitamin D deficiency are persistent fatigue, bone or back pain, muscle weakness or aches, frequent illness, and low mood. Many people have no obvious symptoms at all, which is why deficiency is usually confirmed with a simple blood test rather than symptoms alone.
Common Signs of Vitamin D Deficiency
Persistent Fatigue
Vitamin D plays a role in energy metabolism, and low levels are one of the most frequently overlooked causes of ongoing tiredness, even in people who sleep enough. For a broader look at this symptom, see our guide on why you might always feel tired.
Bone and Back Pain
Vitamin D is essential for calcium absorption and bone mineralisation. When levels are low, bones do not mineralise properly, which can cause dull aching pain, particularly in the lower back, hips, and legs. In severe, prolonged deficiency, this can progress to a condition called osteomalacia, or softening of the bones.
Muscle Weakness and Aches
Vitamin D receptors are present in muscle tissue, and deficiency is linked to muscle weakness, cramping, and an increased risk of falls, particularly in older adults.
Getting Sick Often
Vitamin D supports immune function. People with low levels tend to catch colds, flu, and respiratory infections more frequently and may take longer to recover.
Low Mood, Anxiety or Depression
Vitamin D influences serotonin production in the brain. Research has linked deficiency to a higher likelihood of low mood, anxiety, and depressive symptoms, particularly during winter months when sun exposure is lowest. Our guide on why you might feel anxious for no reason covers this connection in more depth.
Slow Wound Healing
Vitamin D plays a role in producing compounds needed for new skin to form during the healing process. Wounds that heal unusually slowly after surgery or injury can sometimes point to a deficiency.
Hair Loss
While hair loss has many causes, vitamin D deficiency has been associated with certain types of hair loss, including alopecia, since the vitamin plays a role in the hair growth cycle.
Unexplained Weight Gain or Difficulty Losing Weight
Low vitamin D levels have been observed more frequently in people with a higher body weight, and some research suggests low levels may make weight management more difficult, though the relationship works both ways.
Who Is Most at Risk
- People who spend most of their time indoors or live in regions with limited sunlight
- Older adults, whose skin is less efficient at producing vitamin D from sunlight
- People with darker skin, which needs more sun exposure to produce the same amount of vitamin D
- People who are pregnant or breastfeeding
- People with obesity, since vitamin D can be sequestered in fat tissue
- People with conditions affecting nutrient absorption, such as coeliac disease or Crohn’s disease
- People who consistently use high-SPF sunscreen or cover most of their skin outdoors
How Deficiency Is Diagnosed
Vitamin D deficiency is confirmed with a simple blood test measuring 25-hydroxyvitamin D. Levels below 20 ng/mL are generally considered deficient, and levels between 20 and 30 ng/mL are often classed as insufficient, though exact cut-offs can vary slightly by lab and country.
How to Raise Vitamin D Levels
- Spend time outdoors in daylight several times a week, balanced with sensible sun protection
- Eat vitamin D-rich foods such as oily fish, egg yolks, and fortified foods like milk and cereals
- Consider a vitamin D supplement, particularly during autumn and winter, ideally guided by a blood test and your doctor’s advice
- Recheck levels after a few months of supplementation to confirm they have improved
Very high doses of vitamin D can be harmful, so supplementation is best guided by testing rather than guesswork.
When to See a Doctor
See a doctor if you have ongoing fatigue, bone pain, muscle weakness, or low mood that does not have an obvious explanation, especially if you fall into one of the higher-risk groups above. A blood test is quick, inexpensive, and gives a clear answer rather than relying on symptoms alone. Vitamin deficiencies can also show up in less obvious places, such as bleeding gums; our guide on why gums bleed covers this link in more detail.
FAQs
Can vitamin D deficiency cause depression?
Research shows a consistent association between low vitamin D and depressive and anxious symptoms, though it is not considered a sole cause. Correcting a deficiency can help mood in people who are genuinely low, alongside other appropriate treatment.
How long does it take to correct a vitamin D deficiency?
With appropriate supplementation, blood levels typically improve within 8 to 12 weeks, though how quickly symptoms improve varies from person to person.
Can you get enough vitamin D from food alone?
It is difficult, since few foods naturally contain significant amounts. Oily fish and fortified foods help, but sunlight exposure or supplementation is usually needed to reach adequate levels, especially in winter.
Conclusion
Vitamin D deficiency is common and its symptoms are easy to write off as ordinary tiredness or a rough patch. Because a blood test is simple and inexpensive, it is one of the easiest health issues to confirm and correct. If you recognise several of these signs, especially if you fall into a higher-risk group, it is worth asking your doctor for a test rather than guessing.
Last reviewed: August 2026. This article is for general information only and does not replace professional medical advice. Please speak to a GP before starting any supplement.
