Vitamin D Deficiency
Low 25-hydroxyvitamin D, common worldwide, causing musculoskeletal symptoms and bone disease.
Overview
Vitamin D deficiency affects up to 20% of UK adults in winter. Severe deficiency causes osteomalacia in adults and rickets in children. Mild deficiency contributes to muscle weakness, falls and fracture risk in older people.
Symptoms
- • Often asymptomatic
- • Diffuse muscle aches, weakness
- • Bone pain, especially hips, ribs and lower back
- • Frequent infections, low mood (associations, not proven causation)
- • Children: bowed legs, delayed walking, dental enamel defects
Risk factors
- • Housebound or institutionalised
- • Pregnant and breastfeeding women
- • Exclusively breastfed infants without supplementation
- • Obesity (sequestered in adipose tissue)
- • Chronic kidney disease
Causes
- • Limited sunlight exposure (high latitude, covering clothing, sunscreen)
- • Darker skin tones (higher melanin)
- • Older age (reduced cutaneous synthesis)
- • Malabsorption (coeliac, IBD, bariatric surgery)
- • Liver or kidney disease (impaired activation)
- • Drugs: anticonvulsants, glucocorticoids, antiretrovirals
🚨 Red flags — seek urgent care
- • Severe bone pain or proximal muscle weakness — investigate osteomalacia
- • Hypocalcaemia (tetany, seizures)
- • Children with bowing or growth failure
When to seek care
- • Unexplained bone or muscle pain
- • At-risk individuals not on supplementation
- • Fragility fracture or recurrent falls
Diagnosis
- • Serum 25-hydroxyvitamin D: <25 nmol/L deficient; 25–50 insufficient; >50 adequate
- • Calcium, phosphate, alkaline phosphatase, PTH, U&E
- • Bone profile and DEXA if severe or fracture
- • Consider coeliac screen and malabsorption work-up
Treatment
- • Deficient (<25 nmol/L): loading 50,000 IU weekly × 6 weeks or 4000 IU daily × 10 weeks, then 800–2000 IU maintenance
- • Insufficient (25–50 nmol/L): 800–2000 IU daily
- • Add calcium 1000 mg/day if dietary intake low
- • Activated vitamin D (alfacalcidol) in CKD or hypoparathyroidism
- • Treat underlying malabsorption
Prevention
- • All UK adults: consider 10 µg (400 IU) daily October–March
- • Pregnant/breastfeeding women and at-risk groups: year-round supplementation
- • Breastfed infants <1 year: 8.5–10 µg daily
- • Sensible sun exposure (10–15 min, several times per week, outside peak UV)
Complications
- • Osteomalacia, rickets, fragility fractures
- • Falls in older adults
- • Hyperparathyroidism with bone loss
- • Hypocalcaemic seizures (severe)
Prognosis
Symptoms and biochemistry usually correct fully with replacement.
Education & self-care
Most vitamin D deficiency is easy to prevent with sensible sun exposure and a daily supplement in winter. Diagnosis and treatment of true deficiency relieves real symptoms.
Frequently asked questions
Can I overdose on vitamin D?
Toxicity is rare and usually from very high doses (>50,000 IU/day) for prolonged periods. Standard supplementation is safe.
Should everyone take vitamin D?
In the UK, supplementation is advised for all adults in autumn/winter and year-round for at-risk groups.
What level is considered deficient?
Serum 25-hydroxyvitamin D below 25 nmol/L (10 ng/mL) is deficient and warrants treatment. Levels 25–50 nmol/L are insufficient; above 50 nmol/L is generally adequate.
How is deficiency treated?
A loading dose (typically 300,000 IU over several weeks) followed by maintenance (800–2,000 IU daily) corrects most deficiencies. Calcium intake and underlying causes should also be addressed.
Should everyone supplement?
UK guidance recommends 10 mcg (400 IU) daily for all adults during winter, and year-round for those with limited sun exposure, darker skin, pregnancy, infants and older adults.