Does Low Vitamin D Affect Eyesight?
Yes, vitamin D deficiency is significantly associated with multiple forms of visual impairment and eye disease, including dry eye disease, age-related macular degeneration, diabetic retinopathy, and early retinal structural changes that can affect vision quality.
The Evidence for Vitamin D and Eye Disease
While the most recent Endocrine Society guidelines 1 do not specifically address ocular outcomes (focusing primarily on skeletal, cardiovascular, and metabolic diseases), emerging high-quality research from 2025-2026 demonstrates clear associations between vitamin D deficiency and visual impairment.
Dry Eye Disease (Most Robust Evidence)
The strongest evidence links vitamin D deficiency to dry eye disease:
- A 2026 retrospective cohort study of over 12 million patients found that vitamin D deficiency increased the risk of developing dry eye disease by 28.6% (HR 1.286,95% CI 1.277-1.294, p<0.001) 2
- Patients with vitamin D deficiency showed severe deficiency levels (mean 13.79 ng/mL vs 38.13 ng/mL in controls) and had significantly worse tear film stability, reduced tear volume, and more severe symptoms 3
- A 2026 prospective interventional study demonstrated that systemic vitamin D supplementation (50,000 IU weekly for 8 weeks) combined with topical therapy produced greater improvement in tear film parameters compared to topical therapy alone, with adjusted mean difference in tear breakup time of 1.25 seconds (p<0.001) 4
The supplementation study also showed reductions in inflammatory cytokines (TNF-α, IL-1β, IL-4), suggesting vitamin D's anti-inflammatory mechanism contributes to clinical improvement 4.
Retinal Structural Changes
Even in otherwise healthy adults, vitamin D insufficiency (<30 ng/mL) is associated with early subclinical retinal damage 5:
- Reduced central macular thickness (267.66 vs 274.69 μm, p=0.035)
- Decreased perfusion density in deep capillary plexus (all regions p<0.001)
- Lower retinal sensitivity on visual field testing (-2.89 vs -2.16 dB, p=0.003)
These findings suggest vitamin D deficiency may cause measurable structural and functional retinal changes before symptomatic vision loss occurs.
Age-Related Macular Degeneration
A 2025 cross-sectional study found AMD patients had significantly lower serum 25(OH)D levels than controls (22.98 vs 26.12 ng/mL, p=0.013), with late-stage AMD patients showing even lower levels than early-stage patients 6. A systematic review identified that 17 out of 27 studies reported associations between vitamin D and AMD 7.
Diabetic Retinopathy
The systematic review found particularly strong evidence for diabetic retinopathy, with 48 out of 54 studies reporting associations between vitamin D deficiency and DR 7.
Clinical Context: Your Patient with Low Vitamin D and Elevated Homocysteine
In your specific patient with both low vitamin D and elevated homocysteine:
The vitamin D deficiency likely contributes to visual impairment through multiple mechanisms:
- Direct ocular surface effects - causing or exacerbating dry eye symptoms that impair visual quality
- Retinal microvascular compromise - reduced capillary perfusion density affecting retinal function
- Inflammatory pathway activation - increased pro-inflammatory cytokines damaging ocular tissues
- Potential synergistic effect with hyperhomocysteinemia - both are vascular risk factors that may compound retinal damage
Important Caveats
- The Endocrine Society guidelines 1 emphasize that observational associations do not establish causation, and optimal vitamin D levels for extraskeletal outcomes remain uncertain
- Most evidence is observational or from small interventional studies; large randomized controlled trials for ocular outcomes are lacking
- The 2017 ESCEO guidelines 8 note that while mechanistic evidence for extraskeletal effects is strong from in vitro studies, clinical translation remains incompletely established
- However, the 2026 interventional study 4 provides the strongest evidence to date that correcting vitamin D deficiency improves objective ocular parameters
Clinical Recommendation
Given the convergent evidence from multiple 2025-2026 studies showing associations between vitamin D deficiency and measurable visual/ocular impairment, combined with demonstrated benefit from supplementation in the dry eye population, vitamin D deficiency should be considered a modifiable risk factor for visual impairment 2, 5, 4. This is particularly relevant in your patient with concurrent hyperhomocysteinemia, as both represent potentially treatable vascular and inflammatory risk factors.