This was based on a meta-analysis of 10,007 diabetic individuals aged 18 and above, from countries such as the US, Japan, Italy, India, Iran, the Netherlands and China. They were assessed for both vitamin D deficiency and diabetic retinopathy, and those suffering from diabetic retinopathy were shown to have considerably lower serum vitamin D levels than non-sufferers.
The review said, “Diabetic retinopathy is one of the leading causes of blindness worldwide and is the leading cause of blindness for individuals aged 20 to 64 years in the United States.” It went on to state that 20 years after the onset of diabetes, almost all type 1 diabetes patients and over 60% of type 2 diabetes patients are found to have diabetic retinopathy.
Vitamin D is well established as useful in treating inflammation and the formation of new blood vessels. But despite vitamin D receptors having been identified in the human retina and implicated in the development of diabetic retinopathy, the part it plays in the condition has been “obscured in clinical studies by disease pathogenesis, varied diabetic retinopathy classifications, and differing patient ethnic populations”.
Additionally, there are currently no English-language reports on the effect of vitamin D supplementation on diabetic retinopathy in diabetics with a deficiency.
It was also discovered that latitude influences the production of vitamin D under the skin. A previous study had found that people living close the equator had the highest vitamin D levels when compared to people living north and south of the equator.
Patients with diabetic retinopathy living in countries like Lebanon, Italy, China and Japan tended to also have vitamin D deficiency, while diabetics living in countries such as Iran and England did not.
The review conceded that there is a “significant association” between diabetic retinopathy and a lack of vitamin D, as well as a “statistically significant difference” in the mean serum vitamin D levels of sufferers and non-sufferers of diabetic retinopathy.
However, it concluded that “the definitive causative role of vitamin D deficiency and the development of diabetic retinopathy should be explored further”, and that vitamin D supplements “as a protective mechanism against the development and progression of diabetic retinopathy warrants further investigation”.
Source: Canadian Journal of Ophthalmology
“Relationship between vitamin D deficiency and diabetic retinopathy: a meta-analysis”
Authors: Jason Zhang, Sikarin Upala, Anawin Sanguankeo