Vitamin D Deficiency Symptoms – Signs and Causes

What Is Vitamin D Deficiency?

Vitamin D deficiency (medically known as hypovitaminosis D) occurs when the level of vitamin D in the blood falls below a critical threshold. According to the World Health Organization (WHO) and major clinical guidelines, a serum 25-hydroxyvitamin D level below 30 nmol/l (12 ng/ml) is considered deficient, while levels between 30 and 50 nmol/l are regarded as insufficient. Vitamin D is essential for bone health, immune function, muscle strength, and numerous other bodily processes. Deficiency is widespread globally and affects people of all ages.

Causes of Vitamin D Deficiency

The most common cause of vitamin D deficiency is insufficient sun exposure, since approximately 80–90% of the body's vitamin D is produced in the skin upon exposure to UVB radiation. Additional causes include:

• Limited sun exposure: Especially during winter months, working indoors, or wearing covering clothing.
• Older age: The skin's ability to synthesize vitamin D decreases with age.
• Darker skin tone: Higher melanin content reduces the rate of vitamin D production in the skin.
• Malabsorption disorders: Conditions such as celiac disease, Crohn's disease, or fat malabsorption impair the absorption of dietary vitamin D.
• Kidney disease: The kidneys convert vitamin D into its active form (calcitriol); impaired kidney function can lead to deficiency.
• Liver disease: The liver converts vitamin D into its storage form (25-hydroxyvitamin D); liver disorders can disrupt this process.
• Certain medications: Antiepileptics, corticosteroids, and some HIV medications can interfere with vitamin D metabolism.
• Obesity: Vitamin D is stored in fat tissue, making it less bioavailable in people with excess body fat.

Symptoms of Vitamin D Deficiency

Mild vitamin D deficiency often produces no noticeable symptoms. However, a pronounced or long-lasting deficiency can cause a variety of complaints:

General Symptoms

• Fatigue and exhaustion: Persistent tiredness and low energy that does not improve with sleep.
• Mood changes and depression: Vitamin D plays a role in regulating neurotransmitters; deficiency has been linked to depressive symptoms.
• Difficulty concentrating and memory problems: Cognitive impairments may be associated with low vitamin D levels.
• Frequent infections: Since vitamin D supports immune function, deficiency can increase susceptibility to infections.

Muscle and Bone Symptoms

• Bone pain: Particularly in the back, hips, pelvis, and legs; severe deficiency in adults can lead to osteomalacia (softening of the bones).
• Muscle weakness: Especially in the thighs and shoulders; increases the risk of falls in older adults.
• Muscle aches and cramps: Diffuse pain in the muscles and joints.

Symptoms in Children

• Rickets: Severe vitamin D deficiency in childhood can cause rickets, a condition in which bones become soft and deformed. Typical signs include bowed legs, delayed teething, and delayed motor development.
• Growth delays and reduced bone density.

Other Possible Signs

• Hair loss (associated with low vitamin D levels in some studies)
• Slow wound healing
• Bone loss (osteoporosis) with long-term deficiency

At-Risk Groups

Individuals at particular risk for vitamin D deficiency include:

• Older adults (aged 65 and above)
• Infants and toddlers
• Pregnant and breastfeeding women
• People with darker skin tones
• People who spend little time outdoors
• Individuals with chronic bowel, liver, or kidney conditions
• People with obesity

Diagnosis

Vitamin D deficiency is diagnosed through a blood test measuring the level of 25-hydroxyvitamin D (25[OH]D) in the serum. This marker provides the most reliable assessment of the body's vitamin D status. Results are evaluated by a healthcare provider in the context of symptoms and individual risk factors.

Treatment and Supplementation

Treatment of vitamin D deficiency depends on the severity of the deficiency and its underlying cause:

• Supplementation: The most common treatment is vitamin D supplementation (vitamin D3, cholecalciferol). Dosage and duration are determined individually by a physician. Many guidelines recommend a daily intake of 800 IU (20 µg) for adults with insufficient sun exposure.
• Dietary changes: Vitamin D is found in fatty fish (e.g., salmon, herring, mackerel), cod liver oil, eggs, and fortified foods; however, dietary intake alone is usually insufficient to correct a deficiency.
• Increased sun exposure: Regular time outdoors, particularly from spring through early autumn, supports the body's own vitamin D production.
• Treatment of underlying conditions: In secondary deficiency (e.g., caused by malabsorption), the root cause must be addressed.

Important: Vitamin D toxicity from excessive supplementation is possible and can lead to hypercalcemia (elevated calcium levels in the blood). High-dose supplements should only be taken under medical supervision.

References

1. Holick MF. Vitamin D Deficiency. New England Journal of Medicine. 2007;357(3):266–281. doi:10.1056/NEJMra070553
2. World Health Organization (WHO): Vitamin and Mineral Requirements in Human Nutrition. 2nd edition. Geneva, 2004. Available at: https://www.who.int
3. Płudowski P et al. Vitamin D supplementation guidelines. Journal of Steroid Biochemistry and Molecular Biology. 2018;175:125–135. doi:10.1016/j.jsbmb.2017.01.021