In a groundbreaking case-control study published in the February 2024 issue of Clinical Nutrition ESPEN, researchers have uncovered a significant link between vitamin D deficiency and diabetic retinopathy (DR) in individuals with Type 2 diabetes mellitus (T2DM). This study, featuring the combined efforts of a team led by Zahedi Maryam M from the Department of Internal Medicine at Golestan University of Medical Sciences and including experts from ophthalmology, neurology, endocrinology, and nutrition, addresses a critical question in diabetic care: Is vitamin D deficiency associated with retinopathy in type 2 diabetes mellitus?

Diabetic retinopathy, a major complication of diabetes, affects the retina due to prolonged periods of high blood sugar levels. It’s a leading cause of vision impairment and blindness among the working-age population worldwide. As the prevalence of T2DM escalates globally, so does the incidence of DR, making this research particularly pertinent. The study, conducted at the Clinical Research Development Unit (CRDU) of 5 Azar Hospital associated with Golestan University of Medical Sciences, sheds light on the potential of vitamin D as a modifiable risk factor for DR, which could lead to new prevention and treatment strategies.

Methods and Demographics

The team enrolled 201 patients diagnosed with diabetic retinopathy, or DR (the case group), and matched them with 201 T2DM patients without DR (the control group). The participants underwent comprehensive interviews, including questionnaires that covered various demographic variables. Along with these interviews, the study assessed anthropometric measures according to a standard protocol.

Biochemical Assessments

To get a full picture, researchers measured several biochemical indices, such as 25-hydroxyvitamin D, fasting blood glucose (FBG), insulin levels, Glycosylated hemoglobin (HbA1c), total cholesterol (TC), LDL-C (low-density lipoprotein cholesterol), HDL-C (high-density lipoprotein cholesterol), and triglycerides (TG) across all participants.


The data revealed no significant differences between the DR and control groups regarding age, sex, and Body Mass Index (BMI). However, the mean concentration of 25-hydroxyvitamin D was markedly lower in the DR group (14.46 ng/mL) compared to the controls (19.88 ng/mL). Multivariate logistic regression analysis established that lower levels of vitamin D were significantly associated with a heightened risk of developing DR, and by extension, potentially more severe forms such as proliferative diabetic retinopathy (PDR) in T2DM patients.

Conclusions and Implications

The results unequivocally indicate that vitamin D deficiency is a risk factor for retinopathy in individuals with T2DM, suggesting that inadequate levels of this nutrient could precipitate or exacerbate the progression to PDR. Despite the absence of discernible differences in demographic and anthropometric data, vitamin D levels emerged as a distinguishable variable, underscoring the nutrient’s potential role in ocular health within the diabetic population.

According to the authors, these findings could have significant implications. “Based on the results of the present study, vitamin D deficiency increases the risk of diabetic retinopathy in patients with Type 2 diabetes mellitus,” says Dr. Nikpayam O, a co-author from the Department of Nutrition at Golestan University of Medical Sciences. “Also, in case of deficiency of this nutrient, retinopathy may develop into the proliferative type, which is far more severe.”

The declaration in the paper confirms that the authors have noted no conflict of interest, reinforcing the study’s credibility. The article has been indexed with the DOI 10.1016/j.clnesp.2023.11.011, which provides easy access for those wishing to delve deeper into the research methodologies and analyses.

Future Research and Public Health Significance

The study’s results are instrumental in understanding DR’s etiology and could pave the way for vitamin D supplementation as a strategic intervention to reduce the risk of retinopathy among T2DM patients. However, further longitudinal studies and randomized clinical trials are necessary to establish causation and to determine the effectiveness of vitamin D supplementation in preventing and managing DR.

Public health initiatives could benefit from these insights by incorporating vitamin D status monitoring into routine diabetic care, especially considering the simplicity of modulating vitamin D levels through diet, supplements, or modest sunlight exposure. With a growing diabetic population, such adjustments in care protocols could contribute significantly to reducing the global burden of diabetic eye disease.


1. Zahedi, M. M., Motahari, M. M., Fakhri, F., Aphshari, N. M., Poursharif, S., Jahed, R., & Nikpayam, O. (2024). Is vitamin D deficiency associated with retinopathy in type 2 diabetes mellitus? A case-control study. Clinical Nutrition ESPEN, 59, 158-161.

2. International Diabetes Federation. (2019). IDF Diabetes Atlas, 9th edn. Brussels, Belgium: International Diabetes Federation.

3. Chen, S., Grover, D., Optom, B., et al. (2016). Association of vitamin D deficiency and diabetic retinopathy in Asian Indians with Type 2 diabetes. Diabetes Research and Clinical Practice, 123, 90-97.

4. Payne, J. F., Ray, R., Watson, D. G., Delille, C., Rimler, E., & Cleveland, J. (2012). Vitamin D insufficiency in diabetic retinopathy. Endocrine Practice, 18(2), 185-193.

5. Tahrani, A. A., Ball, A., Shepherd, L., Rahim, A., Jones, A. F., & Bates, A. (2010). The prevalence of vitamin D abnormalities in South Asians with type 2 diabetes mellitus in the UK. International Journal of Clinical Practice, 64(3), 351-355.


1. Vitamin D Type 2 Diabetes
2. Diabetic Retinopathy Risk
3. Vitamin D Deficiency
4. Diabetes Eye Complications
5. Proliferative Diabetic Retinopathy