Can low vitamin D (Vitamin D) levels cause illness?

Can Low Vitamin D Cause Illness?

Yes, low vitamin D levels are associated with several illnesses, though the causal relationship and clinical significance remain uncertain for many conditions beyond bone disease. 1

Established Bone-Related Illnesses

Severe vitamin D deficiency definitively causes bone mineralization diseases:

• Rickets in children and osteomalacia in adults result from prolonged, severe deficiency 1, 2
• Osteoporosis and increased fracture risk occur when moderate deficiency leads to elevated parathyroid hormone, triggering bone resorption 3, 4
• These skeletal consequences are the only well-established causal relationships with vitamin D deficiency 1

Associated Non-Skeletal Conditions

Lower vitamin D levels show associations with multiple conditions, though causality is not proven 1:

Cardiovascular Disease

• Studies demonstrate associations between low 25(OH)D levels and cardiovascular mortality, stroke, heart failure, and sudden cardiac death 1
• The relationship appears inconsistent across populations, with white populations showing stronger associations than African Americans 1

Cancer Risk

• Colorectal cancer shows the most consistent inverse relationship with vitamin D levels 1
• Breast cancer risk may be reduced with levels above 20 ng/mL, though prospective studies show heterogeneous results 1
• One randomized trial found 60% lower cancer incidence with 1,100 IU/day supplementation over four years, but this was a secondary outcome 1

Autoimmune Diseases

• Type 1 diabetes risk reduction of 78% was observed with 2,000 IU/day supplementation during infancy in one Finnish cohort 1
• Multiple sclerosis and rheumatoid arthritis show associations with low vitamin D levels 1
• Animal models suggest vitamin D modulates immune differentiation and proliferation 1

Other Conditions

• Falls and functional limitations, particularly in institutionalized elderly populations 1
• Depression, diabetes, and cognitive impairment show associations in observational studies 1, 3
• Muscle weakness and fatigue may occur with moderate deficiency 5

Critical Evidence Limitations

The U.S. Preventive Services Task Force concluded that current evidence is inadequate to determine whether screening for and treating asymptomatic low vitamin D levels improves clinical outcomes in community-dwelling adults 1:

• No consensus exists on the threshold defining deficiency 1
• Associations vary by cut-point used (20 ng/mL vs 30 ng/mL), population, and setting 1
• Most evidence comes from observational studies, not randomized controlled trials with clinical outcomes as primary endpoints 1, 6

Important Paradox

African Americans have lower vitamin D levels than white persons but paradoxically lower fracture rates, suggesting total serum 25(OH)D may not accurately reflect bioavailable vitamin D across all populations 1

Prevalence of Deficiency

Depending on the threshold used, vitamin D deficiency affects 19-77% of the U.S. population 1, 5:

• 33% have levels ≤20 ng/mL 1, 5
• 77% have levels <30 ng/mL 1

Clinical Bottom Line

While severe deficiency unequivocally causes bone disease, the evidence linking moderate vitamin D deficiency to non-skeletal illnesses remains largely associational rather than causal 1. Treatment should focus on preventing and treating established bone disease, with supplementation for other conditions considered investigational pending results from ongoing trials like VITAL 1.