What causes vitamin D deficiency?

Causes of Vitamin D Deficiency

Vitamin D deficiency is primarily caused by inadequate sun exposure, limited dietary intake, and impaired absorption, which can significantly impact bone health and increase risk for chronic diseases. 1

Major Risk Factors

Decreased Vitamin D Synthesis

• Inadequate sun exposure is a primary cause of vitamin D deficiency, particularly in people:
  • Living at high latitudes 1, 2
  • During winter months when UVB radiation is reduced 1, 3
  • Who practice physical sun avoidance (including sunscreen use) 2, 3
  • Who routinely wear clothing that prevents sun exposure on most of the skin 2
• Darker skin pigmentation reduces the skin's ability to produce vitamin D in response to UVB exposure:
  • African Americans, Hispanics, and Asians have significantly lower 25-(OH)D levels than white populations 2, 1
  • 70.6% of African Americans and 44.2% of Hispanics have 25-(OH)D levels ≤20 ng/mL compared to 21.7% of white persons 2

Decreased Intake and Absorption

• Limited dietary vitamin D intake contributes to deficiency as few foods naturally contain significant amounts 1, 4
• Malabsorptive conditions impair vitamin D absorption:
  • Inflammatory bowel disease 2, 1
  • History of gastric bypass surgery 2, 1
  • Other malabsorptive disorders 4

Physiological and Demographic Factors

• Obesity is associated with lower vitamin D levels due to:
  • Greater sequestration of vitamin D into adipose tissue 2, 1
  • Possibly increased vitamin D requirements 2
• Advanced age increases risk due to:
  • Age-related decreases in cutaneous synthesis capacity 1, 5
  • Often reduced outdoor activities and sun exposure 6
  • Potentially decreased dietary intake 6
• Being homebound or institutionalized significantly limits sun exposure 2

Clinical Implications

• Severe vitamin D deficiency can lead to:
  • Rickets in children 7
  • Osteomalacia in adults (painful bone disease where new bone is not properly mineralized) 5, 7
• Less severe deficiency is associated with:
  • Increased parathyroid hormone levels leading to bone resorption 5
  • Osteoporosis and increased fracture risk 5, 6
  • Muscle fatigue and weakness 1, 7
  • Increased risk for falls, especially in elderly 1

Prevalence

• Approximately 33% of the U.S. population had 25-(OH)D levels ≤20 ng/mL from 2001-2006 2, 1
• 77% had levels below 30 ng/mL from 2001-2004 2
• Testing rates for vitamin D levels are increasing despite uncertainty about the definition of deficiency 2

Important Considerations

• The threshold for vitamin D deficiency is debated, but serum 25-(OH)D levels below 75 nmol/L (30 ng/mL) are often considered suboptimal 5
• Vitamin D testing methods vary, with 10-20% variability between assay methods and laboratories 2
• While low vitamin D levels are more common in certain populations (e.g., African Americans), the clinical significance may differ between racial/ethnic groups 2
• 25-(OH)D may act as a negative acute-phase reactant, with levels decreasing in response to inflammation 2