Researchers studied whether vitamin D levels affect the health of tears in your eyes. They compared 34 people with low vitamin D to 34 people with normal vitamin D levels, all without dry eye symptoms. Using special eye imaging technology, they measured different aspects of the tear film that coats your eyes. They found that people with low vitamin D had slightly thinner tear layers compared to those with healthy vitamin D levels. While both groups seemed fine on the surface, the findings suggest that vitamin D might play a role in keeping your eyes’ protective tear layer healthy.

The Quick Take

  • What they studied: Whether people with low vitamin D have different tear film measurements compared to people with normal vitamin D levels, even if they don’t have dry eye symptoms.
  • Who participated: 68 adults total—34 with low vitamin D levels and 34 with healthy vitamin D levels. All participants did not have symptoms of dry eye disease.
  • Key finding: People with low vitamin D had measurably thinner tear layers (both height and depth) compared to those with normal vitamin D. The differences were small but statistically significant, suggesting vitamin D may influence tear film quality.
  • What it means for you: If you have low vitamin D, your tear film might be thinner even if your eyes don’t feel dry yet. This could potentially matter for long-term eye health, though more research is needed. Getting adequate vitamin D may help protect your eyes’ natural moisture layer.

The Research Details

This was a comparative study where researchers divided 68 people into two groups based on their blood vitamin D levels. One group had low vitamin D (insufficient levels), and the other group had healthy vitamin D levels. All participants had no symptoms of dry eye disease at the start. The researchers used advanced eye imaging technology called spectral domain optical coherence tomography (SD-OCT)—think of it as a special camera that takes detailed pictures of the front part of your eye. They measured specific features of the tear meniscus, which is the curved layer of tears that sits along your eyelid. They also did standard eye tests like the Schirmer test (which measures tear production) and tear break-up time (which measures how long tears stay on your eye before breaking apart).

This research approach is important because it looks for early signs of tear film changes before people actually feel symptoms of dry eyes. By comparing people with low vitamin D to healthy controls, researchers can see if vitamin D status affects tear quality even when people don’t realize there’s a problem. This helps scientists understand whether vitamin D plays a preventive role in eye health.

This study has moderate strength. The sample size of 68 people is reasonable for this type of research. The researchers used objective measurements (special imaging technology) rather than just asking people how they felt, which makes the results more reliable. However, this is a single study with a relatively small group, so the findings need to be confirmed by other researchers before making major changes. The study was well-designed with clear comparison groups, which strengthens the conclusions.

What the Results Show

The main finding was that tear meniscus height (TMH)—the thickness of the tear layer—was significantly lower in people with low vitamin D compared to those with healthy vitamin D levels. Tear meniscus depth (TMD)—another measure of tear layer size—was also significantly lower in the low vitamin D group. Both of these differences were small in absolute terms, but they were statistically significant, meaning they’re unlikely to have happened by chance. Interestingly, when researchers looked at standard dry eye tests like the Schirmer test and tear break-up time, both groups appeared normal. This suggests that vitamin D insufficiency may cause subtle changes to the tear film that don’t yet cause noticeable symptoms.

The Ocular Surface Disease Index (OSDI) score, which measures dry eye symptoms, was slightly higher in the low vitamin D group, though still in the normal range. This means people with low vitamin D reported slightly more eye discomfort, but not enough to be considered dry eye disease. Other measurements like tear turbidity (cloudiness) and the percentage of particles in the tear layer showed no significant differences between groups.

Previous research has suggested that vitamin D plays a role in eye health and that vitamin D deficiency is linked to dry eye disease. This study adds to that body of knowledge by showing that even before people develop noticeable dry eye symptoms, low vitamin D is associated with measurable changes in tear film structure. The findings support the idea that vitamin D may be important for maintaining healthy tears throughout life.

This study has several important limitations. First, it’s relatively small with only 68 participants, so the findings need to be confirmed in larger groups. Second, it’s a snapshot in time—researchers only measured each person once, so they can’t prove that low vitamin D causes tear changes (only that they’re associated). Third, the study didn’t look at whether vitamin D supplements could improve tear film measurements. Finally, the differences found were small, and it’s unclear how much these subtle changes matter in real-world eye health.

The Bottom Line

Based on this research, maintaining healthy vitamin D levels appears to support eye health. If you have low vitamin D, getting your levels checked and addressing the deficiency may help protect your tear film. However, this single study isn’t strong enough to recommend vitamin D supplements specifically for eye health—more research is needed. General vitamin D recommendations (from sun exposure, diet, or supplements as advised by your doctor) remain important for overall health and may benefit your eyes too. Confidence level: Moderate—this is promising evidence but needs confirmation.

This research is most relevant for people with low vitamin D levels, people at risk for dry eyes, and those interested in preventive eye health. It’s particularly important for people who spend long hours on screens, live in areas with limited sunlight, or have other risk factors for dry eyes. People already diagnosed with dry eye disease should discuss vitamin D status with their eye doctor. This research is less immediately relevant for people with healthy vitamin D levels and no eye concerns, though maintaining adequate vitamin D is still important for overall health.

If you address low vitamin D through supplements or lifestyle changes, you wouldn’t expect immediate changes to your tear film. Eye tissue changes typically take weeks to months to develop or improve. If you start vitamin D supplementation, give it at least 2-3 months before expecting to notice any difference in eye comfort or dryness.

Want to Apply This Research?

  • Track your vitamin D supplementation or sun exposure daily, and rate your eye comfort on a scale of 1-10 weekly. Note any changes in dryness, grittiness, or irritation over time.
  • If you have low vitamin D, set a reminder to take a vitamin D supplement daily (if recommended by your doctor), and track compliance in the app. Also log outdoor time, as natural sunlight helps your body produce vitamin D.
  • Create a long-term tracking dashboard that shows vitamin D intake/sun exposure alongside eye comfort ratings. After 8-12 weeks, review the data to see if improving vitamin D status correlates with better eye comfort. Share this data with your eye doctor at your next visit.

This research suggests an association between vitamin D levels and tear film measurements but does not prove that vitamin D deficiency causes dry eyes or that supplementation will prevent them. This information is for educational purposes only and should not replace professional medical advice. If you have concerns about dry eyes, vitamin D deficiency, or eye health, consult with an eye care professional or your primary care doctor. Do not start vitamin D supplements without discussing it with your healthcare provider, especially if you take other medications or have existing health conditions.