What causes severe vitamin D deficiency?

Causes of Severe Vitamin D Deficiency

The primary causes of severe vitamin D deficiency include inadequate sun exposure, limited dietary intake, malabsorption conditions, severe liver or kidney disease, and certain medications that interfere with vitamin D metabolism. 1, 2

Definition of Severe Vitamin D Deficiency

Severe vitamin D deficiency is typically defined as serum 25-hydroxyvitamin D (25-OHD) levels:

• <30 nmol/L (<12 ng/mL) 2, 3
• This level dramatically increases the risk of bone mineralization diseases, mortality, and infections 3

Major Causes of Severe Vitamin D Deficiency

1. Inadequate Sun Exposure

• Limited outdoor activities 4
• Living at high latitudes 1
• Routinely wearing clothing that covers most of the skin 1
• Being homebound or institutionalized 1
• Air pollution reducing UVB exposure 4
• Reduced endogenous synthesis in the presence of jaundice 1

2. Decreased Dietary Intake

• Low consumption of vitamin D-rich foods (fish, cod liver oil, dairy products, fortified foods) 1
• Very few foods naturally contain significant vitamin D 5

3. Malabsorption Conditions

• Inflammatory bowel disease 1
• Celiac disease
• History of gastric bypass surgery 1
• Other malabsorptive disorders 1

4. Impaired Metabolism

• Severe liver disease (impairs 25-hydroxylation of vitamin D) 1
• Severe kidney disease (impairs 1-hydroxylation) 1
• Nephrotic syndrome (urinary losses of 25-hydroxyvitamin D and vitamin D-binding protein) 1

5. Demographic and Physical Factors

• Darker skin pigmentation (increased melanin reduces vitamin D synthesis) 1
• Obesity (vitamin D sequestration in adipose tissue) 2
• Advanced age (decreased skin synthesis capacity) 1, 6

6. Other Contributing Factors

• Chronic illness and being bedridden 1
• Pregnancy and breastfeeding (increased requirements) 6

High-Risk Populations

Several populations are at particularly high risk for severe vitamin D deficiency:

• Patients with chronic kidney disease 1
• Patients with chronic liver disease 1
• Elderly individuals, especially those who are institutionalized 1, 6
• Individuals with darker skin pigmentation 1
• Those with limited sun exposure due to cultural practices or geographic location 1
• Patients with malabsorption syndromes 1

Clinical Implications

Severe vitamin D deficiency can lead to:

• Rickets in children and osteomalacia in adults 1, 6
• Increased risk of fractures and bone loss 1
• Secondary hyperparathyroidism 1
• Increased mortality risk 3
• Higher susceptibility to infections 3
• Potential associations with cardiovascular disease, metabolic syndrome, and certain cancers 6

Diagnostic Approach

When severe vitamin D deficiency is suspected:

• Measure serum 25-hydroxyvitamin D level (the best indicator of vitamin D status) 2
• Consider checking calcium, phosphorus, and parathyroid hormone levels to assess for metabolic consequences 1
• Evaluate for underlying conditions that may contribute to deficiency

Understanding these causes is essential for effective prevention and treatment of severe vitamin D deficiency, which remains a significant global health issue affecting approximately 1 billion people worldwide 4.