Researchers studied 150 people with type 2 diabetes to understand if vitamin D levels affect the tiny blood vessels in the eyes. Using special imaging technology, they found that people with low vitamin D had fewer healthy blood vessels in their retinas (the light-sensitive part of the eye). This connection was especially strong in people with early-stage diabetic retinopathy, a condition where diabetes damages eye blood vessels. The findings suggest that maintaining healthy vitamin D levels might be important for protecting eyesight in people with diabetes.

The Quick Take

  • What they studied: Whether vitamin D levels affect the tiny blood vessels in the eyes of people with type 2 diabetes and early diabetic retinopathy
  • Who participated: 150 people with type 2 diabetes, some with early signs of diabetic retinopathy (eye damage from diabetes). Researchers examined 286 eyes total using advanced imaging technology
  • Key finding: People with low vitamin D had noticeably fewer healthy blood vessels in their retinas compared to those with adequate vitamin D levels. This was true for both the shallow and deep layers of blood vessels in the eye
  • What it means for you: If you have type 2 diabetes, maintaining adequate vitamin D levels may help protect your eyesight. However, this study shows a connection, not proof that vitamin D prevents eye damage. Talk to your doctor about checking your vitamin D levels and getting regular eye exams

The Research Details

This was a cross-sectional study, which means researchers looked at a group of people at one point in time rather than following them over months or years. They recruited 150 people with type 2 diabetes and examined 286 eyes using a special imaging technology called optical coherence tomography angiography (OCTA). This technology takes detailed pictures of the tiny blood vessels in the retina without needing injections or dyes.

Researchers measured three important things: how many blood vessels were in the retina (vessel density), the size of the clear area in the center of the retina where blood vessels don’t normally grow (called the foveal avascular zone), and how thick the retina was. They also measured each person’s vitamin D levels and a hormone called parathyroid hormone, which increases when vitamin D is low.

Using statistical analysis, they looked for connections between vitamin D levels and the measurements from the eye imaging. This approach allowed them to see if people with different vitamin D levels had different patterns of blood vessel damage.

This research matters because diabetic retinopathy is a leading cause of vision loss in working-age adults, and early detection is crucial. By understanding whether vitamin D plays a role in eye blood vessel damage, doctors might be able to identify another factor they can help patients control. The study used advanced imaging technology (OCTA) that can detect very small changes in blood vessels before a person notices vision problems, making it possible to catch damage early

This study has some strengths: it used objective, high-quality imaging technology to measure blood vessel changes, and it included a reasonable number of participants. However, because it’s a cross-sectional study, it shows a connection between vitamin D and eye blood vessel changes but cannot prove that low vitamin D causes the damage. The study was conducted at one point in time, so we don’t know if vitamin D levels changed over time or how that affected results. The findings need to be confirmed by larger studies that follow people over several years

What the Results Show

The main finding was clear: people with low vitamin D had fewer healthy blood vessels in their retinas. This was true for both the superficial vascular complex (the layer of blood vessels closest to the surface of the retina) and the deep vascular complex (the deeper layer of blood vessels). The reduction in blood vessels was directly related to how low the vitamin D levels were—the lower the vitamin D, the fewer blood vessels were present.

Another important finding involved the foveal avascular zone, which is the small clear area in the center of the retina where blood vessels don’t normally grow. In people with low vitamin D and high parathyroid hormone levels, this clear area was larger than normal. An enlarged clear area suggests that blood vessels are being lost or damaged in that region.

The researchers found that vitamin D deficiency was an independent risk factor for retinal blood vessel damage. This means that even after accounting for other factors like blood sugar control and blood pressure, low vitamin D was still connected to blood vessel problems. This strengthens the suggestion that vitamin D itself may play a protective role in keeping eye blood vessels healthy.

The study also measured retinal thickness, though the results for this measurement were less dramatic than the blood vessel findings. The connection between vitamin D and parathyroid hormone levels was notable—when vitamin D was low, parathyroid hormone was high, and this combination was associated with the most significant blood vessel changes. This suggests that the vitamin D system in the body may be important for maintaining healthy eye blood vessels

Previous research on vitamin D and diabetic retinopathy has shown mixed results, which is why this study was needed. Some earlier studies suggested vitamin D might protect against eye damage in diabetes, while others found no connection. This research adds to the growing evidence that vitamin D deficiency may be harmful to the tiny blood vessels in the eye. However, the relationship is still not completely understood, and more research is needed to determine if vitamin D supplements can actually prevent or slow eye damage

This study has several important limitations. First, it’s a snapshot in time—researchers looked at people once rather than following them over months or years to see if vitamin D changes affected their eyes. Second, the study can show that low vitamin D and blood vessel damage occur together, but it cannot prove that low vitamin D causes the damage. Third, the study doesn’t tell us whether taking vitamin D supplements would help prevent or improve eye damage. Fourth, all participants had type 2 diabetes and early-stage eye damage, so the results may not apply to people with diabetes who don’t have eye problems or to people with type 1 diabetes. Finally, the study was conducted in one location, so results might differ in other populations with different genetic backgrounds or lifestyles

The Bottom Line

If you have type 2 diabetes, ask your doctor to check your vitamin D level. If it’s low, discuss whether vitamin D supplementation is appropriate for you. Additionally, get regular eye exams (at least annually) to monitor for diabetic retinopathy, especially if you have vitamin D deficiency. These recommendations are based on moderate evidence that vitamin D may play a protective role in eye health. However, vitamin D supplementation is not yet proven to prevent or treat diabetic retinopathy, so it should be part of a comprehensive diabetes care plan that includes blood sugar control, blood pressure management, and regular eye exams

This research is most relevant to people with type 2 diabetes who have early signs of diabetic retinopathy or who are at risk for it. It’s also important for people with type 2 diabetes and vitamin D deficiency. People with type 1 diabetes should discuss these findings with their eye doctor, as the results may or may not apply to them. If you don’t have diabetes, this research doesn’t directly apply to you, though maintaining adequate vitamin D is important for overall health

If you start vitamin D supplementation after being deficient, it typically takes 2-3 months for blood levels to normalize. However, improvements in eye blood vessel health would take much longer to detect—likely several months to a year or more. This is why regular eye exams are important; they can track changes over time. Don’t expect immediate improvements in vision or eye health; any benefits would develop gradually

Want to Apply This Research?

  • Track your vitamin D supplementation daily (if prescribed) and record your vitamin D blood test results when available. Set reminders for annual eye exams and log the results, including any changes in retinal vessel density or other measurements if your eye doctor provides them
  • If your doctor recommends vitamin D supplementation, use the app to set daily reminders to take your supplement at the same time each day. Also use the app to schedule and track your regular eye exams (at least annually) and any follow-up appointments with your eye doctor
  • Create a long-term tracking system that records: (1) vitamin D supplementation adherence, (2) vitamin D blood test results and dates, (3) eye exam dates and any findings, (4) blood sugar control metrics, and (5) any vision changes you notice. Review this data quarterly with your healthcare team to assess whether your vitamin D management is supporting your eye health

This research shows a connection between low vitamin D and blood vessel changes in the eyes of people with type 2 diabetes, but it does not prove that vitamin D supplements will prevent or treat diabetic retinopathy. This article is for educational purposes only and should not replace professional medical advice. If you have type 2 diabetes or concerns about your vision, consult with your doctor or eye specialist before starting any supplements or making changes to your diabetes care plan. Regular eye exams and good blood sugar control remain the most important ways to protect your eyesight if you have diabetes.