By now, the importance of vitamin D in preventing disease and protecting overall health has been scientifically proven. Beyond its most well-known role in building strong, healthy bones, vitamin D has been shown to help protect against many health conditions, including various forms of cancer, cardiovascular disease, respiratory infections, diabetes and multiple sclerosis.
And now, new research has shown that a deficiency in vitamin D could also lead to one of the most common causes of blindness — diabetic retinopathy.
Diabetic retinopathy is caused by changes in the blood vessels in the retina. In some people, the blood vessels leak fluid. In others, abnormal blood vessels grow on the surface of the retina, causing vision changes. The disease has four main stages:
1. Mild Non-proliferative Retinopathy: This is the earliest stage, where small areas of swelling occur in the blood vessels.
2. Moderate Non-proliferative Retinopathy: At this stage, some blood vessels in the retina become blocked.
3. Severe Non-proliferative Retinopathy: A more advanced stage, this is where many blood vessels become blocked and the retina starts to become deprived of blood supply.
4. Proliferative Retinopathy: At this most advanced stage, the retina sends messages to the body that it needs nourishment because so many blocked blood vessels have deprived it of nutrients. This triggers the growth of abnormal new blood vessels, which in and of itself isn’t a bad thing. The problem is that these new vessels are extremely thin-walled and fragile, making them highly susceptible to leakage, which ultimately leads to vision loss and blindness.
In this study, researchers examined 200 patients (52 percent female, 48 percent male) who had either type 1 or type 2 diabetes for at least 11 years. All patients gave blood samples after overnight fasting to check levels of vitamin D and parathyroid hormone (PTH), a protein hormone that controls calcium, phosphorus and vitamin D levels in the blood and bones. Vitamin D deficiencies are associated with higher levels of PTH. (Too much PTH can also reduce glucose tolerance.)
In addition to the blood work, patients underwent thorough eye exams at the start of the study, with results showing:
- 21 percent did not have any form of retinopathy
- 19 percent had mild non-proliferative retinopathy
- 17.5 percent had moderate non-proliferative retinopathy
- 20.5 percent had severe or very severe non-proliferative retinopathy
- 22 percent had proliferative retinopathy
After analyzing the vitamin D levels in the blood samples, researchers found that, overall, the concentrations of this nutrient were significantly lower in patients with retinopathy than those who did not have the condition.
There was also a significant negative correlation between the levels of vitamin D in the blood and the severity of the condition. In mild non-proliferative retinopathy, the level of vitamin D in the blood was 67.4 +/- 13.7 pmol/L, while in the most severe form of proliferative retinopathy, the level was 34.1 +/- 17.2 pmol/L.
As for PTH, the levels of this protein increased as retinopathy status worsened, with levels the highest in those patients who had either severe non-proliferative retinopathy or proliferative retinopathy.
There are many possible reasons for this link between vitamin D deficiencies and diabetic retinopathy. For starters, vitamin D has immune-enhancing, anti-inflammatory, antioxidant and antiproliferative functions in all areas of the body, including in the eyes. Furthermore, vitamin D inhibits angiogenesis — the growth of new, abnormal blood vessels.
How to Get Sufficient Levels of Vitamin D
As you probably know, the easiest way for your body to get the vitamin D it needs is to go outside every single day, exposing your unprotected skin to direct sunlight for at least 20-30 minutes before applying sunscreen.
If you can’t get outside every day, or if your doctor advises you to avoid direct sunlight without sun protection, then you can get vitamin D by consuming foods fortified with the nutrient (dairy products, for instance), or by taking a supplement.
Make sure you choose a vitamin D product that contains D3 in the form of cholecalciferol — the form best absorbed and utilized by the body. For most healthy individuals, we recommend a daily dosage of 500-2,000 IU per day. If you’re looking for a high-quality vitamin D supplement, you can click here.
If you are concerned that you are deficient in vitamin D, or if you have diabetes or diabetic retinopathy and want to protect your eyes by ensuring proper levels of vitamin D in your system, ask your doctor to order a vitamin D profile blood test. If your levels do turn out to be low, then work with your doctor to find a dosage level that is appropriate for you to protect your eyes.
 Raheem RNAMA and Fattah MAHMA. Serum vitamin D and parathormone (PTH) concentrations as predictors of the development and severity of diabetic retinopathy. Alex J Med. 2012, http://dx.doi.org/10.1016/j.ajme.2012.08.006.
 Shokravi MT et al. Vitamin D inhibits angiogenesis in transgenic murine retinoblastoma. Invest Ophtalmol Vis Sci. 1995;36:83-7.