What Happens If Vitamin D Deficiency Is Left Untreated
Severe and prolonged vitamin D deficiency causes bone mineralization diseases—rickets in children and osteomalacia in adults—which are the most clinically significant consequences requiring urgent treatment. 1
Established Skeletal Consequences
The only well-established causal relationships with vitamin D deficiency involve skeletal consequences. 2
Bone Mineralization Diseases
- Vitamin D deficiency impairs calcium homeostasis, leading to poor mineralization of the collagen matrix in bones. 1
- In children, this manifests as rickets with growth retardation and bone deformities. 3
- In adults, poor mineralization of newly laid bone matrix results in osteomalacia, a painful bone disease. 3
Secondary Hyperparathyroidism and Bone Loss
- When calcium absorption becomes insufficient, parathyroid hormone production increases to mobilize calcium from bones, creating secondary hyperparathyroidism. 3
- This triggers bone resorption, leading to loss of bone matrix and minerals. 1
- Fracture risk increases significantly, particularly in white populations and institutionalized individuals. 1
Neuromuscular Effects
- Vitamin D deficiency causes muscle weakness and fatigue, directly increasing fall risk. 1
- Falls are especially problematic in institutionalized elderly populations, where low vitamin D levels show significantly increased fall risk. 1
- Falls lead to 40% of all nursing home admissions and are the largest single cause of injury-related deaths in elderly people. 4
Associated Cardiovascular and Metabolic Effects
While causality is not definitively proven, observational evidence shows concerning associations:
Cardiovascular Disease
- 25(OH)D levels below 15 ng/mL are associated with excess cardiovascular events compared to levels above 30-40 ng/mL. 1
- Lower vitamin D levels show associations with cardiovascular mortality, stroke, heart failure, and sudden cardiac death, though the relationship appears inconsistent across populations. 2
- Low vitamin D status is linked to arterial hypertension, with modest but significant blood pressure reductions seen with supplementation in hypertensive patients. 1
Cancer Risk
- Colorectal cancer shows the most consistent inverse relationship with vitamin D levels. 2
- One randomized trial found 60% lower cancer incidence with 1,100 IU/day supplementation over four years. 2
- Breast cancer risk may be reduced with levels above 20 ng/mL, though evidence is heterogeneous. 2
Autoimmune and Metabolic Conditions
- Type 1 diabetes risk reduction of 78% was observed with 2,000 IU/day supplementation during infancy in one Finnish cohort. 2
- Multiple sclerosis and rheumatoid arthritis show associations with low vitamin D levels. 2
- Depression, diabetes, and cognitive impairment show associations in observational studies. 2
Critical Clinical Context
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. 2
Important Caveats
- Most evidence for non-skeletal effects comes from observational studies, not randomized controlled trials with clinical outcomes as primary endpoints. 2
- No consensus exists on the threshold defining deficiency, and associations vary by cut-point used, population, and setting. 2
- The relationship between low vitamin D and cardiovascular disease appears stronger in white populations than African Americans. 2
Prevalence
- Depending on the threshold used, vitamin D deficiency affects 19-77% of the U.S. population. 2
- 33% have levels ≤20 ng/mL, and 77% have levels <30 ng/mL. 2
When Treatment Is Clearly Indicated
Deficiency defined as 25(OH)D levels below 20 ng/mL requires active treatment, with a target level of at least 30 ng/mL. 1
Treatment is most clearly beneficial for: