Dr. Smriti Jain, J18842, Dr. B Chandra Sekharan, Dr. Lubhani Jain
“A CLINICAL STUDY OF VITAMIN D SUPPLEMENTATION IN DIABETIC RETINOPATHY PATIENTS WITH TYPE 2 DIABETES MELLITUS”
INTRODUCTION
Diabetes Mellitus continues to be a major health burden all over the world. According to the latest data by the world health organisation, almost 422 million individuals are estimated to be suffering from diabetes mellitus.[1] The increasing trend towards unhealthy food practices, sedentary lifestyle and physical inactivity can be attributed to this rise in the burden of diabetes mellitus.
Diabetic Retinopathy remains a leading cause of blindness all over the world especially in the individuals in the working age group with maximum patients presenting in the late stages with significant visual loss due to lack of awareness.
Vitamin D deficiency has been implied as a risk factor for development of diabetes mellitus and cardiovascular disorders by several studies. [2][3]
Serum vitamin D levels have an anti- inflammatory action. They decrease the release of pro-inflammatory cytokines, proliferation of lymphocytes and natural killer cells and have a role in preventing angiogenesis thereby implicating a protective role against development of diabetic retinopathy.[4][5]
AIMS AND OBJECTIVES
AIMS
To evaluate the effect of supplementation of Vitamin D in delaying the progression, the association of serum 25 hydroxy Vitamin D with the level of Diabetic Retinopathy, and its use as a predictor of the severity of Diabetic Retinopathy.
PRIMARY OBJECTIVE
To evaluate whether the oral supplementation of vitamin D delays the progression of Diabetic Retinopathy.
SECONDARY OBJECTIVE
To evaluate the association between serum 25 hydroxy Vitamin D and the level of Diabetic Retinopathy
To evaluate whether 25 hydroxy Vitamin D level can be used as a predictor of the severity of Diabetic Retinopathy.
MATERIALS AND METHODS
SUBJECT SELECTION:
40 patients with type 2 diabetes mellitus and diabetic retinopathy were included in this prospective, interventional study which was carried out at the department of vitreo-retina services, Regional Institute of ophthalmology and Government ophthalmic hospital, Madras Medical College, Chennai, over a period of 1 year.
Inclusion criteria:
- Patients must be aged 18 years and above.
- Patients with type 2 Diabetes Mellitus who are diagnosed as Non Proliferative Diabetic Retinopathy or Proliferative Diabetic Retinopathy
Exclusion criteria:
- Patients with type 1 Diabetes
- Patients previously on vitamin D supplementation.
- Use of medications known to influence mineral metabolism including calcitonin, growth hormone, thiazide diuretics, anti-convulsants such as Carbamazepine, phenytoin and phenobarbitone or excessive doses of vitamin A (> 20,000 units/day).
- History of disorders that are known to affect the metabolism of Vitamin D and major medical illness including renal failure, hepatic dysfunction, and musculoskeletal disorders were excluded
- Serum calcium < 8 or > 11 mg/dL
- Patients on hormone replacement therapy, steroids or testosterone.
PROCEDURE
HISTORY:
All patients were screened with a detailed history including nature & duration of symptoms, duration of exposure to sunlight, diet history and history of tobacco chewing or alcohol consumption. History of treatment with oral hypoglycaemic agents, insulin, vitamin supplements and other drug intake, disorders known to influence Vitamin D levels and previous ophthalmic surgery/laser or other medical treatment history was also taken.
Patients then underwent a complete systemic and ocular examination.
GENERAL EXAMINATION
General vital data like pulse, blood pressure, peripheral pulses were noted. Height (in meters) and weight (in kgs) was recorded and systemic examination of CNS, CVS, RS and abdomen was done.
OCULAR EXAMINATION
- Visual acuity was assessed by Snellen’s chart and refractive status was noted
- Anterior segment evaluation with slit lamp biomicroscopy was performed
- Intraocular pressure was measured using Goldmann Applanation tonometer
- Diabetic retinopathy was evaluated by a dilated fundus examination using 90D & indirect ophthalmoscopy
- Fundus photographs were taken for documentation
- All patients will underwent Fundus fluorescein angiography and OCT to assess maculopathy if present
- The levels of retinopathy will then be classified as per the ETDRS.
INVESTIGATIONS
Fasting blood glucose levels (FBS), Post prandial blood glucose levels (PPBS), urine sugar and albumin and serum Calcium were measured. Measurement of serum 25 hydroxy Vitamin D and HbA1C was be done prior to and following 6 months of oral vitamin D supplementation.
Twenty patients received daily oral supplementation of 2000 IU of Vitamin D for a duration of 6 months, constituting the treatment arm, while the other 20 patients served as the control arm.
FOLLOW UP PROCEDURES/ VISITS
Patients were re-examined every month. At each visit visual acuity recording, anterior segment examination by slit lamp biomicroscopy, tonometry and dilated fundus examination was done. Any progression of retinopathy was noted. Fundus photographs were repeated at each visit. Fundus fluorescein angiography was repeated at 3 months and 6 months. OCT to re-assess maculopathy, was repeated at 3 and 6 months, or earlier in selected patients if deemed necessary. Fasting and post prandial blood glucose levels (FBS and PPBS) and urine sugar and albumin were measured to ensure glycaemic control. Compliance with oral Vitamin D supplementation therapy was ensured by counting the empty medicine strips at each visit and history of Vitamin D toxicity if any was elicited.
ASSESSMENT OF PARAMETERS
- The level and severity of diabetic retinopathy
- Improvement in Best corrected visual acuity (logMAR conversion of Snellen’s chart)
BIOCHEMICAL ESTIMATION OF VITAMIN D
IN SERUM
In our study, the direct, competitive chemiluminescent immunoassay (CLIA) method was used for quantitative estimation of 25- hydroxy Vitamin D. This is a United States Food and Drug Administration (FDA)–approved immunoassay method. This method was developed in 2002 and measured total 25-hydroxy vitamin D in serum samples. Hepatic metabolism converts Vitamin D3 and D2 to 25-hydroxyvitamin D. Serum or plasma 25-OH vitamin D levels is the best indicator of vitamin D nutritional status.
PERFORMANCE SPECIFICATIONS
The measurement range is from 4 to 150 ng/ml.
SAMPLE REQUIREMENTS
- Human serum samples
- Samples may be collected after an overnight fast, however this is not essential
- Infected and haemolysed samples must be rejected
EPARATION OF SAMPLES
At least 250 µL of sample is essential for the first test. Frozen samples must be thawed and mixed thoroughly until a homogeneous specimen is obtained.
STORAGE OF SAMPLES
Samples are stored in the frozen state (-20˚C or below) in glass or plastic vials without any additives or preservatives.
REAGENTS
- Anti 25 OH Vitamin D antibody coated magnetic particles
- Conjugate used is an isoluminol derivative, in phosphate buffer with EDTA, preservatives, surfactants and 10% ethanol
PRINCIPLE OF THE TEST
It is a two step incubation procedure. The initial step involves a separation of 25-hydroxy vitamin D from its binding protein, which is followed by making it bind to the specific solid phase antibody. This is followed by the addition of vitamin D-isoluminol tracer after 10 minutes. A wash cycle is then used to remove unbound material following the second 10 minute incubation period. Chemiluminescent reaction is initiated by adding the starter reagents. The photomultiplier detects the light signal, the strength of which is used to determine the 25-hydroxy vitamin D levels. The light signal, indicated in relative light units bears a negative relation with 25 hydroxy vitamin D levels.
REFERENCE VALUES OF 25 HYDROXY VITAMIN D
Deficiency : <20 ng/ml
Insufficiency : 20 – 30 ng/ml
Sufficiency : 30 – 100 ng/ml
Toxicity : >150 ng/ml
STATISTICAL ANALYSIS
Data analysis was carried out by the Statistical Package For Social Science (SPSS). Quantitative data were presented as means and standard deviation and qualitative data were expressed as numbers or percent.
OBSERVATION AND RESULTS
40 patients were enrolled in this study. 20 patients received oral Vitamin D supplementation, serving as the case group and the remaining 20 patients served as the control group.
Age distribution
Table 1. Age distribution of a total of 40 patients in
the case and control arm.
| Age in years | No. of patients – Case group | No. of patients – control group | Total no. of patients |
| 41-45 | 1 | 2 | 3 (7.5%) |
| 46-50 | 1 | 3 | 4 (10%) |
| 51-55 | 6 | 6 | 12 (30%) |
| 56-60 | 4 | 3 | 7 (17.5%) |
| 61-65 | 4 | 4 | 8 (20%) |
| 66-70 | 3 | 2 | 5 (12.5%) |
| 71-75 | 1 | 0 | 1 (2.5%) |
Chart 1. Age distribution
In this study patients between 51-55 years were maximally affected (30%). The oldest patient enrolled was 72 years, while the youngest patient was 43 years. The mean age at presentation was 58.85 ± 7.09 years in the case group and 56.50 ± 7.72 years in the control group.
Sex distribution
Table 2.Distribution of males and females
| Sex | No. of patients – case group | No. of patients – control group | Total no. of patients |
| Male | 9 | 12 | 21 (53.5%) |
| Female | 11 | 8 | 19 (47.5%) |
Chart 2. Sex wise distribution
21 (53.5%) males and 19 (47.5%) females were affected with diabetic retinopathy in this study.
Laterality and symmetry
Table 3. Symmetry of involvement of eyes
| No. of patients – case group | No. of patients – control group | Total patients | |
| Symmetrical involvement | 18 | 19 | 37 (92.5%) |
| Asymmetrical involvement | 2 | 1 | 3 (7.5%) |
Chart 3. Symmetry of involvement of eyes
All patients enrolled in this study had bilateral disease, however the severity of diabetic retinopathy was asymmetrical in 3 patients (7.5%). The remaining 37 cases (92.50%) had a bilaterally symmetrical presentation of diabetic retinopathy. The age and sex distribution and the symmetry of involvement were not significantly different between the cases and controls (p>0.05).
Severity of diabetic retinopathy at presentation
Table 4. Classification of patients based on severity of retinopathy at presentation
| Severity of retinopathy | No. of patients – case group | No. of patients – control group | Total patients |
| Moderate NPDR | 5 | 5 | 10 |
| Severe NPDR | 5 | 5 | 10 |
| Very severe NPDR | 5 | 5 | 10 |
| Early PDR | 5 | 5 | 10 |
Table 5.Classification of eyes based on severity of retinopathy at presentation
| Severity of retinopathy | No. of eyes in case group | No of eyes in control group | Total no. of eyes |
| Moderate NPDR | 11 | 11 | 22 (27.5%) |
| Severe NPDR | 9 | 9 | 18 (22.5%) |
| Very severe NPDR | 11 | 10 | 21 (26.3%) |
| Early PDR | 9 | 10 | 19 (23.8%) |
Chart 4.Distribution of eyes based on severity of retinopathy at presentation
In both the case and control group, 5 patients each were diagnosed with moderate NPDR, severe NPDR, very severe NPDR and early PDR. None of the patients were diagnosed with mild NPDR or high-risk PDR at presentation. In patients with asymmetrical disease, the eye with increased severity of retinopathy was used to decide the level of retinopathy to which the patient must be assigned to.
Of the 80 eyes studied, 22 eyes (27.5%) had moderate NPDR, 18 eyes (22.5%) had severe NPDR, 21 eyes (26.3%) had very severe NPDR and 19 eyes (23.8%) had early PDR. The distribution of severity of retinopathy at presentation was not significantly different between the case and control groups by Pearson’s Chi Square test (p=0.992).
Best Corrected Visual Acuity at baseline
Table 6.BCVA at baseline
| Visual Acuity | Case group | Control group | ||
| No.of eyes | % | No.of eyes | % | |
| 3/60 – 6/60 | 6 | 15 | 6 | 15 |
| 6/36 – 6/24 | 8 | 20 | 9 | 22.5 |
| 6/18 – 6/12 | 19 | 47.5 | 17 | 42.5 |
| 6/9 – 6/6 | 7 | 17.5 | 8 | 20 |
Chart 5.BCVA at baseline
After logMAR conversion, the mean BCVA was found to be 0.5085 ± 0.33059 in the cases and 0.5250 ± 0.33429 in the controls which was not found to be significantly different, with a two-tailed p-value of 0.828 by unpaired t-test.
Treatment of retinopathy
Table 7.Treatment of retinopathy
| Treatment of retinopathy | No. of eyes – cases | No. of eyes – controls |
| Grid laser photocoagulation | 30 | 30 |
| Pan-retinal
photocoagulation |
29 | 31 |
Chart 6.Distribution of retinopathy
Patients in the case as well as control group continued to receive laser treatment in the form of pan-retinal photocoagulation or grid photocoagulation during the course of the study. The number of eyes receiving grid laser photocoagulation was 30 patients each in the case and control groups, while those receiving pan-retinal photocoagulation were 29 and 31 patients respectively in the case and control groups.
HbA1c levels at baseline
Table 8.Distribution of HbA1c levels according to the
severity of retinopathy
| Severity of retinopathy | Mean (in %) | Standard deviation | Mean (in %) | Standard deviation | P value |
| Moderate NPDR | 7.140 | 0.270 | 7.160 | 0.288 | 0.9126 |
| Severe NPDR | 7.540 | 0.055 | 7.520 | 0.084 | 0.6666 |
| Very severe NPDR | 7.880 | 0.084 | 7.9 | 0.082 | 0.7294 |
| Early PDR | 8.3 | 0.1 | 8.3 | 0.115 | 1.0 |
| Total | 7.715 | 0.460 | 7.715 | 0.459 | 1.0 |
Table 9.Distribution of HbA1c levels
| Serum HbA1c levels | No. of patients | ||||
| Moderate NPDR | Severe NPDR | Very severe NPDR | Early PDR | Total patients | |
| 6.0%-7.0% | 4 | 0 | 0 | 0 | 4 (10%) |
| 7.0%-8.0% | 6 | 10 | 8 | 0 | 24 (60%) |
| 8.0%-10% | 0 | 0 | 2 | 10 | 12 (30%) |
Chart 7.Distribution of HbA1c levels according to severity of retinopathy
The mean serum HbA1c levels were 7.715 ± 0.460% in cases and 7.715 ± 0.459% in controls, which was not found to be significantly different (two-tailed p value=1.0 by unpaired t-test). The levels of serum HbA1c were highest in patients with early PDR in both cases and controls and progressively decreased with decreasing severity of retinopathy, being lowest in patients with moderate NPDR.
Of the 40 patients enrolled in the study, a majority (60%) of the patients demonstrated fair gylcaemic control (serum HbA1c = 7.0%-8.0%), 30% of the patients showed unsatisfactory control (serum HbA1c = 8.0%-10.0%) and the remain 10% of patients demonstrated good glycaemic control (serum HbA1c = 6.0%-7.0%)
Serum FBS levels
Table 10.FBS Levels in diabetic retinopathy
| Severity of retinopathy | FBS levels | ||||
| Mean (in mg/dl) | Standard deviation | Mean (in mg/dl) | Standard deviation | P value | |
| Moderate NPDR | 131.4 | 8.96 | 131.25 | 11.44 | 0.9830 |
| Severe NPDR | 146.8 | 6.42 | 147.2 | 10.43 | 0.9436 |
| Very severe NPDR | 154.6 | 4.04 | 153.6 | 3.71 | 0.6943 |
| Early PDR | 171.2 | 7.09 | 170.4 | 8.11 | 0.8722 |
| Total | 151.0 | 16.0 | 150.8 | 16.14 | 0.9688 |
Chart 8.Baseline serum FBS levels in diabetic retinopathy
The mean serum fasting blood sugar levels were 151 ± 16 mg/dl and 150 ± 16.14 mg/dl in the cases and control groups respectively, which did not differ significantly (two-tailed p value=0.9688 by unpaired t-test). The levels of serum FBS were highest in patients with early PDR in both cases and controls and progressively decreased, being lowest in patients with moderate NPDR. The levels of both HbA1c and FBS did not differ significantly between cases and controls having moderate, severe, very severe NPDR and early PDR (p > 0.05).
Serum 25 hydroxy Vitamin D levels at baseline
Table 11.Distribution of baseline serum 25 hydroxy vitamin D levels
| Serum 25 hydroxy Vitamin D levels (ng/ml) | No. of patients | ||||
| Moderate NPDR | Severe NPDR | Very severe NPDR | Early PDR | Total patients | |
| <20 | 8 | 8 | 9 | 10 | 35 (87.5%) |
| 20-30 | 1 | 1 | 1 | 0 | 3 (7.5%) |
| 30-100 | 1 | 1 | 0 | 0 | 2 (5%) |
| >100 | 0 | 0 | 0 | 0 | 0 |
Table 12. Distribution of baseline serum 25 hydroxy vitamin D levels according to severity of retinopathy
|
Severity of retinopathy |
Mean Vitamin D levels (ng/ml) | Standard deviation | Minimum Vitamin D levels (in ng/ml) | Maximum vitamin D level (in ng/ml) |
| Moderate NPDR | 27.573 | 6.0525 | 18.8 | 42.5 |
| Severe NPDR | 22.518 | 3.6956 | 18.3 | 32.3 |
| Very severe NPDR | 17.557 | 1.7105 | 15.8 | 21.1 |
| Early PDR | 12.131 | 2.7112 | 9.1 | 17.7 |
| Total | 19.945 | 6.9074 | 9.1 | 42.5 |
Chart 9 Mean 25 hydroxy Vitamin D levels at baseline according to severity of retinopathy
A total of 35 patients (87.5%) enrolled in the study were found to have Vitamin D deficiency (serum 25 hydroxy vitamin D: < 20 ng/ml), 3 patients (7.5%) were found to have Vitamin D insufficiency (serum 25 hydroxy vitamin D : 20-30 ng/ml) and 2 patients (5%) were found to have normal Vitamin D levels.
By One way ANOVA with Post Hoc tests and Tukey HSD, a highly significant p value of less than 0.001 was obtained, indicating that the levels of serum 25 hydroxy Vitamin D measured in the 40 patients at baseline were significantly lowered as the severity of retinopathy increased from moderate NPDR to early PDR. The patients with moderate NPDR had a mean value of serum 25 hydroxy vitamin D of 27.573 ng/ml, which decreased to 22.518 ng/ml and 17.557 ng/ml in patients with severe and very severe NPDR respectively and patients with early PDR had the lowest value of serum 25 hydroxy vitamin D of 12.131 ng/ml.
Pearson correlation test, showed a two-tailed significance of – 0.841, indicating a strongly negative correlation between serum 25 hydroxy Vitamin D levels with the severity of diabetic retinopathy as documented at baseline in all 40 patients. Hence as the serum levels of 25 hydroxy Vitamin D decreased, the severity of diabetic retinopathy was found to increase.
The mean serum 25 hydroxy Vitamin D levels were 19.775 ± 5.663 ng/ml and 20.115 ± 8.101 ng/ml in the case and control groups respectively at presentation and did not differ significantly between the two groups, having a two-tailed p value of 0.8793 by the unpaired t-test.
Serum 25 hydroxy Vitamin D levels at 6 months
Chart10.Serum 25 hydroxy Vitamin D at baseline and 6 months
The mean serum 25 hydroxy Vitamin D levels were 42.4930 ± 9.9332 ng/ml and 20.1305 ± 1.7346 ng/ml in the case and control group respectively at the end of 6 months, which was significantly higher in the case group following 6 months of oral supplementation than the control group. A two-tailed p value of 0.8793 by the unpaired t-test was obtained.
The mean serum 25 hydroxy Vitamin D levels were 20.1150 ± 8.1012 ng/ml and 20.1305 ± 7.7575 ng/ml in the control group at baseline and at 6 months respectively, showing a no significant difference with a two-tailed p value of 0.9585 by the paired t-test.
Table 13.Distribution of serum 25 hydroxy Vitamin D levels at 6 months in cases
| Serum 25 hydroxy Vitamin D3 levels (ng/ml) in cases at 6 months | No. of patients | percentage |
| <20 | 0 | 0 |
| 20-30 | 4 | 10% |
| 30-100 | 16 | 80% |
| >100 | 0 | 0 |
Following 6 months of oral supplementation of Vitamin D, 80% cases attained normal serum 25 hydroxy vitamin D levels (30-100 ng/ml), 10% patients remained insufficient (20-30 ng/ml) and none of the patients remained deficient (<20 ng/ml). None of the cases attained toxic serum levels of 25 hydroxy vitamin D (>100 ng/mg).
Severity of retinopathy – at 1 month follow up
Table 14.Severity distribution of retinopathy at 1 month
| Severity of retinopathy at 1 month | No. of eyes in case group | Percentage in case group | No of eyes in control group | Percentage in control group |
| Moderate NPDR | 11 | 27.5% | 11 | 27.5% |
| Severe NPDR | 9 | 22.5% | 9 | 22.5% |
| Very severe NPDR | 11 | 27.5% | 10 | 25% |
| Early PDR | 9 | 22.5% | 10 | 25% |
At 1 month follow up, 27.5% of eyes in both the case and control groups were found to have moderate NPDR and 22.5% eyes in both groups had severe NPDR. 27.5% of eyes among the cases had very severe NPDR, compared to 25% of controls and 22.5% of eyes in the case group had early PDR compared to 25% of eyes of controls. The severity of diabetic retinopathy noted at 1 month follow up did not differ significantly between the cases and controls (2-sided p=0.992 according to Pearson Chi-Square test).
Severity of retinopathy – at 3 months follow-up
Table 15.Severity distribution of retinopathy at 3 months
| Severity of retinopathy at 3 month | No. of eyes in case group | Percentage in case group | No of eyes in control group | Percentage in control group |
| Moderate NPDR | 11 | 27.5% | 11 | 27.5% |
| Severe NPDR | 9 | 22.5% | 9 | 22.5% |
| Very severe NPDR | 11 | 27.5% | 10 | 25% |
| Early PDR | 9 | 22.5% | 2 | 5% |
| High-risk PDR | 0 | 0 | 8 | 20% |
Chart 12.Severity distribution at 3 months
At 3 months, there was no progression noted in the patients found to have moderate, severe and very severe NPDR in both groups, with 27.5% of the eyes of cases and controls having moderate NPDR and 22.5% of the eyes patients in both groups having severe NPDR. 27.5% of cases had very severe NPDR, compared to 25% of controls and 22.5% of cases had early PDR compared to 25% of controls. 27.5% and 25% of the eyes of cases and controls respectively were found to have very severe NPDR. 22.5% eyes with early PDR in the case group did not progress at 3 months. However in the control group 8 eyes (20%) with early PDR at 1 month progressed to high risk PDR. This progression from early PDR to high-risk PDR in the control group, compared to no such progression among the cases was found to be statistically significant (2-sided p=0.014 according to Pearson Chi-Square test).
Severity of retinopathy – at 6 months
Table 16. Severity distribution of retinopathy at 6 months
| Severity of retinopathy at 6 month | No. of eyes in case group | Percentage in case group | No of eyes in control group | Percentage in control group |
| Moderate NPDR | 11 | 27.5% | 11 | 27.5% |
| Severe NPDR | 8 | 20% | 5 | 12.5% |
| Very severe NPDR | 10 | 25% | 1 | 2.5% |
| Early PDR | 7 | 17.5% | 12 | 30% |
| High-risk PDR | 4 | 10% | 11 | 27.5% |
Chart 13. Severity distribution at 6 months
At 6 months, none of the eyes with moderate NPDR progressed in both groups, with 27.5% of the eyes of cases and controls having moderate NPDR. Severe NPDR was found in 20% and 12.5 % of eyes of cases and controls respectively. Very severe NPDR was found in 25% of eyes of cases and 2.5% of eyes of controls. 17.5% and 30% of eyes of the cases and controls were found to have early PDR. High risk PDR had developed in 10% of eyes of cases and 27.5% of eyes of controls. Hence at 6 months majority of eyes of cases showed moderate NPDR while majority of eyes of controls showed early PDR.
Hence at 6 months, eyes with severe, very severe NPDR and early PDR were found to have progressed in both groups, however the progression was significantly greater in controls then in cases (2-sided p=0.013 according to Pearson Chi-Square test).
BCVA at 6 month
Table 17.BCVA at 6 months
| Visual Acuity | Case group | Control group | ||
| No.of eyes | % | No.of eyes | % | |
| 3/60 – 6/60 | 5 | 12.5 | 3 | 7.5 |
| 6/36 – 6/24 | 3 | 7.5 | 4 | 10 |
| 6/18 – 6/12 | 23 | 57.5 | 20 | 50 |
| 6/9 – 6/6 | 9 | 22.5 | 13 | 32.5 |
Chart 14.BCVA at 6 months
After logMAR conversion, the mean best corrected visual acuity was found to be 0.4265 ± 0.3311 in the cases and 0.3750 ± 0.2507 in the controls which was not found to be significantly different, with a two-tailed p-value of 0.435 by unpaired t-test.
After logMAR conversion at 6 months, the mean best corrected visual acuity improved significantly from 0.5085 ± 0.3360 at baseline to 0.4265 ± 0.3311 at 6 months in the 40 eyes enrolled in the case group (two-tailed p value=0.0324 by paired t-test). A significant improvement was also found in the 40 eyes of controls from a mean BCVA of 0.5250 ± 0.3443 at baseline to 0.3750 ± 0.2507 at 6 months (two-tailed p value=0.0008 by paired t-test).
DISCUSSION
Diabetic retinopathy remains one of the leading causes of visual loss in the working-age people. After duration of diabetes exceeding 15 years, it affects three out of four diabetic patients.
In our study 75% of patients belonged to the 6th and 7th decades of life. This may be due to the fact that prevalence of systemic diseases such as diabetes and hence its resulting microvascular complications, increases with increasing age. The youngest patient enrolled was 43 years and the oldest was 72 years. Previous studies revealed a similar age distribution. (Daniel M.Taylor et al. Survey ophthalmology).[6]
In our study, 53.5% males and 47.5% females were affected with diabetic retinopathy. Although an increased percentage of males were found to be affected, no significant male preponderance was observed. This finding was consistent with previous studies.
All patients enrolled in this study had bilateral disease, however the severity of diabetic retinopathy was asymmetrical in 7.5% of patients.
Among the 80 eyes studies, 27.5% had moderate NPDR, 22.5% had severe NPDR, 26.3% had very severe NPDR and 23.8% had early PDR. 71.5% eyes had maculopathy associated with retinopathy. In the Oman study, 60% of the eyes had NPDR, 18% had PDR and 24% of eyes had associated maculopathy. This increased incidence in our study, could be attributed to the late presentation of diabetic patients for ophthalmological screening due to decreased awareness.
In our study, baseline mean serum HbA1c levels were 7.715 +/- 0.460% in cases and 7.715 +/- 0.459% in controls. The baseline mean serum fasting blood sugar levels were 151 +/- 16 mg/dl and 150 +/- 16.14 mg/dl in the cases and control groups respectively. The levels of serum HbA1c and fasting blood glucose were highest in patients with early PDR progressively decreased, being lowest in patients with moderate NPDR, findings that were supported by the DCCT study and the study by Kroc Collaborative Study Group. [7][8]
87.5% of patients enrolled in the study were found to have Vitamin D deficiency (serum 25 hydroxy vitamin D: < 20 ng/ml), 7.5% were found to have Vitamin D insufficiency (serum 25 hydroxy vitamin D : 20-30 ng/ml) and 2 patients 5% were found to have normal Vitamin D levels.
The levels of serum 25 hydroxy Vitamin D measured in the 40 patients at baseline were significantly lower as the severity of retinopathy increased from moderate NPDR to early PDR. The patients with moderate NPDR had a mean value of serum 25 hydroxy vitamin D of 27.573 ng/ml, which decreased to 22.518 ng/ml and 17.557 ng/ml in patients with severe and very severe NPDR respectively and patients with early PDR had the lowest value of 12.131 ng/ml. Hence our study demonstrated an inverse relationship between the severity of diabetic retinopathy and serum 25 hydroxy Vitamin D levels, findings which were supported by several other studies.
A strongly negative correlation between serum 25 hydroxy Vitamin D levels and severity of diabetic retinopathy was documented, suggesting that neovascularization in the retina may involve a decrease in serum 25(OH) D concentrations in patients with diabetic retinopathy. Hence, low serum levels of 25 (OH) D may have an association with uncontrolled angiogenesis and the progression of DR as demonstrated by Aksoy H. et. Al.[9]
A cross-sectional study of type 2 diabetic patients conducted by Suzuki A et. Al. showed a significant association between the existence of proliferative retinopathy and a decrease in 25(OH) D.[10] Investigators found a decrease in 25(OH) D according to the number of microvascular complications present. These findings were also supported by a study conducted by Joergensen C et. Al.[11] A clinic-based, cross-sectional study by Paynes et. Al. to assess the relationship between vitamin D status and diabetic retinopathy concluded that diabetic subjects, especially those with PDR, have lowered 25(OH) D levels than those without diabetes.[12] Our findings were also in agreement with the study done by Hulya et al. who demonstrated an inverse relationship between the severity of the retinopathy and retinal neovascularisation with serum 1,25(OH) 2 D3 concentrations, levels being the lowest in PDR and the highest in diabetic patients without retinopathy.[13]
In order to evaluate whether Vitamin D supplementation delayed the progression of diabetic retinopathy, 40 eyes each in the case and control group were followed up, on a monthly basis for 6 months and the severity of retinopathy was documented. The case and control groups did not differ significantly in the age, sex distribution, duration of diabetes, associated systemic diseases such as hypertension, treatment modalities of diabetes and retinopathy, severity distribution of retinopathy, associated maculopathy and serum HbA1c, fasting blood glucose and 25 hydroxy vitamin D.
The mean serum 25 hydroxy Vitamin D level of 42.4930 ng/ml was attained in the cases following 6 months of oral supplementation, suggesting that this dose used was adequate for normalisation of serum vitamin D levels according to our study. The mean levels remained deficient (20.1305 ng/ml) in the controls at the end of 6 months.
There was a wide variation in the duration, dosage and mode of supplementation used in previous studies. The present “no observed adverse effect limit” of 2000 IU daily has been found to be too low at least by 5-fold.[14]
In human beings, serum 25 hydroxy vitamin D has been found to have a half life of about 1 month. A minimum of 4 half lives are required before a drug attains an equilibrium concentration. However the concentrations of serum 25 hydroxy vitamin D have been found to change depending on its synthesis and clearance. Hence it has been suggested that it attains a stable serum concentration much earlier. Moreover Davie MW et. Al. demonstrated that 25 hydroxy vitamin D attains a plateau level by 1 month of supplementation.[15] Hence an oral dose of 2000 IU daily was used for 6 months supplementation in our study.
At 1 month follow up, none of the 80 eyes showed progression. At 3 months, there was no progression noted in the patients with moderate, severe and very severe NPDR in both groups. However a significantly increased progression from early PDR to high-risk PDR was found in the control group. While none of the eyes with early PDR in the case group were found to have progressed, 8 eyes (20%) with early PDR in the control group at 1 month had progressed to high risk PDR.
At 6 months, none of the eyes with moderate NPDR progressed in both groups, however eyes with severe, very severe NPDR and early PDR were found to have progressed in both groups, this progression being significantly greater in controls then cases. Severe NPDR was found in 20% and 12.5 % of eyes of cases and controls respectively. Very severe NPDR was found in 25% of eyes of cases and 2.5% of eyes of controls. 17.5% and 30% of eyes of the cases and controls were found to have early PDR. High risk PDR had developed in 10% of eyes of cases and 27.5% of eyes of controls.
The BCVA was found to improve significantly from baseline in both cases and controls, however no difference in BCVA or was observed between the two groups at 6 months. This suggests that no additional improvement in BCVA was obtained with vitamin D supplementation, over and above the recommended treatment for diabetic retinopathy.
None of the cases developed any complications relating to Vitamin D toxicity at this dosage recommendation.
SUMMARY
40 patients with type 2 diabetes mellitus and diabetic retinopathy were included in this prospective, interventional study which was carried out at the department of vitreo-retina services, Regional Institute of ophthalmology and Government ophthalmic hospital, Madras Medical College, Chennai, over a period of 1 year.
The aim was to evaluate the effect of supplementation of Vitamin D in delaying the progression of diabetic retinopathy, to study the association of serum 25 hydroxy Vitamin D with the level of Diabetic Retinopathy, and its use as a predictor of the severity of Diabetic Retinopathy.
20 patients received daily oral supplementation of 2000 IU of Vitamin D for a period of 6 months constituting the case arm, while the other 20 patients served as the control arm.
75% of patients enrolled in the study belonged to the 6th and 7th decades of life. 53.5% males and 47.5% females were affected with diabetic retinopathy in this study.
Among the 80 eyes studies, 27.5% had moderate NPDR, 22.5% had severe NPDR, 26.3% had very severe NPDR and 23.8% had early PDR. 71.5% eyes had maculopathy associated with retinopathy.
Our study demonstrated an inverse relationship between the severity of diabetic retinopathy and serum 25 hydroxy Vitamin D levels at baseline. Patients with moderate NPDR had a mean serum 25 hydroxy vitamin D of 27.573 ng/ml, which decreased to 22.518 ng/ml and 17.557 ng/ml in patients with severe and very severe NPDR respectively and patients with early PDR had the lowest value of 12.131 ng/ml.
The mean serum 25 hydroxy Vitamin D level of 42.4930 ng/ml was attained in the cases following 6 months of oral supplementation.
At 1 month follow up, none of the 80 eyes showed progression. At 3 months, there was no progression noted in the patients with moderate, severe and very severe NPDR in both groups. 8 eyes (20%) with early PDR in the control group at 1 month had progressed to high risk PDR. No such progression was noted in cases with early PDR.
At 6 months, none of the eyes with moderate NPDR progressed in both groups, however eyes with severe, very severe NPDR and early PDR were found to have progressed in both groups, this progression being significantly greater in controls then cases.
Severe NPDR was found in 20% and 12.5 % of eyes of cases and controls respectively. Very severe NPDR was found in 25% of eyes of cases and 2.5% of eyes of controls. 17.5% and 30% of eyes of the cases and controls were found to have early PDR. High risk PDR had developed in 10% of eyes of cases and 27.5% of eyes of controls.
The BCVA was found to improve significantly from baseline in both cases and controls, however no difference in BCVA between the two groups at 6 months.
None of the cases developed any complications relating to Vitamin D toxicity.
LIMITATIONS OF THE STUDY
Limitations of our study were the small sample size and short follow up period of 6 months. Larger study group is necessary to quantify the actual magnitude of benefit of vitamin D supplementation in diabetic retinopathy. Longer follow up is necessary to document whether the beneficial effect of such supplementation is seen in mild and moderate NPDR as well.
CONCLUSION
From the results of our study we can conclude that oral supplementation of Vitamin D in addition to the recommended treatment with photocoagulation, delays the progression of severe, very severe and early PDR.
This beneficial effect was observed with an oral dose of 2000 IU daily for 6 months. No toxicity of Vitamin D was noted at this dosage.
An inverse relation between the level of Serum 25 hydroxy vitamin D concentrations and the severity of diabetic retinopathy was noted.
Our study demonstrated that low levels of vitamin D may be a risk marker of development or progression of diabetic retinopathy. It may be advisable to conduct ophthalmologic examination at increased frequency in diabetics whose serum 25 hydroxy vitamin D concentrations are diminished. Serum 25 hydroxy vitamin D concentrations could become a useful biochemical marker to predict the severity of DR in patients with diabetes mellitus in the future.
No additional improvement in BCVA was obtained with vitamin D supplementation, over and above the recommended treatment for diabetic retinopathy.
Further studies with a longer follow-up period and larger sample size are warranted to assess the association between serum 25 hydroxy vitamin D levels and diabetic retinopathy and the efficacy and safety of vitamin D supplementation in delaying the progression of diabetic retinopathy.
REFERENCES
- World Health Organization,Global Report on Diabetes. Geneva, 2016
- Baz-Hecht M, Goldfine AB. The impact of vitamin D deficiency on diabetes and cardiovascular risk.Curr Opin Endocrin Diab Obes. 2010;17:113–119
- Judd SE, Tangpricha V. Vitamin D deficiency and risk for cardiovascular disease. Am J Med Sci.2009;338(1):40–44
- Palomer X, Gonzalez-Clemente JM, Blanco-Vaca F, Mauricio D. Role of vitamin D in the pathogenesis of type 2 diabetes mellitus.Diabetes Obes Metab. 2008;10:185–197
- Albert DM, Scheef EA, Wang S, et al. Calcitriol is a potent inhibitor of retinal neovascularization. Invest Ophthalmol Vis Sci. 2007;48:2327–2334.
- Daniel M.Taylor et al. Survey ophthalmology
- The Diabetes Control; Complications Trial Research Group. (1993). “The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus”. N Engl J Med. 329 (14): 977–86
- Kroc Collaborative Study Diabetes1985 Aug; 34(Supplement 3): 5-12
- Aksoy H, Akcay F, Kurtul N, Baykal O, Avci B. Serum 1,25 dihydroxy vitamin D (1,25(OH)2D3), 25 hydroxy vitamin D (25(OH)D) and parathormone levels in diabetic retinopathy.Clin Biochem. 2000;33:47–51.
- Suzuki A, Kotake M, Ono Y, Kato T, Oda N, Hayakawa N, et al. Hypovitaminosis D in type 2 diabetes mellitus: Association with microvascular complications and type of treatment.Endocr J. 2006;53:503–10.
- Joergensen, P. Hovind, A. Schmedes, H.-H. Parving, and P. Rossing, “Vitamin D levels, microvascular complications, and mortality in type 1 diabetes,”Diabetes Care, vol. 34, no. 5, pp. 1081–1085, 2011.
- F. Payne, R. Ray, D. G. Watson et al., “Vitamin D insufficiency in diabetic retinopathy,”Endocrine Practice, vol. 18, no. 2, pp. 185–193, 2012
- Aksoy H, Akcay F, Kurtul N, Baykal O, Avci B. Serum 1,25 dihydroxy vitamin D (1,25(OH)2D3), 25 hydroxy vitamin D (25(OH)D) and parathormone levels in diabetic retinopathy.Clin Biochem. 2000;33:47–51.
- Vieth R1. Am J Clin Nutr.1999 May;69(5):842-56
- Davie MW, Lawson DE, Emberson C, Barnes JL, Roberts GE, Barnes ND. Vitamin D from skin: contribution to vitamin D status compared with oral vitamin D in normal and anticonvulsant-treated subjects.Clin Sci1982;63:461–72