European Journal of Cardiovascular Medicine

Diabetes is a chronic, metabolic disease characterized by elevated levels of blood glucose. Type 2 Diabetes mellitus (T2DM) is the most common type, usually in adults, which occurs when the body becomes resistant to insulin or doesn't make enough insulin. “About 422 million people worldwide have diabetes, the majority living in low-and middle-income countries, and 1.5 million deaths are directly attributed to diabetes each year. Both the number of cases and the prevalence of diabetes have been steadily increasing over the past few decades” [1].It is projected that by 2025 the number of cases with diabetes in India would be 69.9 million with a vast majority still undiagnosed [2]. Depression is common in patients with diabetes [3] and it is known to be twice as frequent in patients with diabetes17.6%, as in the general population (9.3%) [4]. Despite the negative impact of untreated depression on diabetes care and prognosis, depression is still under recognised in patients [5]. In a meta-analysis done in 2018 about the prevalence of depression among type 2 diabetes mellitus patients in India was found to be 38% and they reported that high prevalence of depression among T2DM patients was found [6].

It was an observational cross sectional analytical study. Institutional ethical committee clearance was taken, the ID being 035A/2022 and informed consent was taken from the participants. People with Type 2 Diabetes Mellitus (T2DM) who came to the outpatient Diabetology department of a tertiary care teaching hospital in Andhra Pradesh were the study subjects. The study period was for2 months- September and October, 2022. The study sample included all consecutive patients with T2DM who came to the Diabetology department during the two months of the study. The inclusion criteria were, patients of both sexes with type 2 diabetes (age: >30 years) and patients on metformin therapy. The exclusion criteria were pregnant women, Patients with prior history of depression before onset of diabetes and patients on anti-depressant therapy Patients meeting the desired criteria, who consented to participate, were taken for the study. They were screened for depression and serum Vitamin B12 values were estimated. The study tools used were, Case record form and Patient health Questionnaire- 9 (PHQ-9). Socio-demographic data of the patient like age, sex, duration of diabetes, duration of metformin therapy were asked and recorded in the case study form. Screening for depression was carried out by PHQ-9. It was self-administered by the patient and the completed questionnaire was verified for positive responses and diagnostic algorithms were applied. The questionnaire consists of 9 items and a score from 0 to 3 is given for each question (0-not at all, 1-several days, 2-more than half the days, 3-nearly every day). Scores from all columns are added to get a total score (maximum score-27). Patients were classified as having moderate-severe depressive symptoms when they had a score ≥10 on PHQ-9 and those with a score <10 were classified as having minimal/mild depressive symptoms [16].

Our study reported serum vitamin B12values < 200 pg/ml (148 pmol/L) were found in 9 subjects out of a total of 56, which is considered as deficient. There is as yet no uniformity in studies as to the serum level of B12 which may be considered deficient. We have followed the Mayo guidelines which have been followed by several other studies [18-20].

Our study did not show a significant relation between A1c values and PHQ-9 scores. We had taken a cut off of PHQ-9 ≥10 to be clinically depressed and A1c of ≥7 to indicate dysglycemia. Spearman’s correlation between these two variables shows a value of 0.00194, with a p value of 0.987 which is not statistically significant. This indicates that the glycemic status has no association with depression in our study. Hasanovic et al [21]in their cross sectional study with 150 subjects with Type 2 Diabetes (T2DM) observed that higher values of A1c is associated with depression as evidenced by the PHQ-9 score. Several studies too have reported the same. [22-24]. We could not find any association probably due to the insufficient sample size as the sample was collected over a period of 2 months. Langberg et al also reported no association between the two variables. But their study also suffered from inadequate power of the sample [25].

In our study we observed a moderate negative correlation between metformin dosage and B12 serum values (coefficient -0.316, p 0.01). This is similar to a study by Jiwoon et al. They found that metformin dose ≥ at 1500 mg per day could be a major factor vitamin B12 deficiency [26]. It was a cross sectional study done on 1111 patients with T2DM for 6 months. A value <300 pg/ml (222 pmol/L) was considered deficient. Serum vitamin B12 deficiency occurred in 22.2% of patients (n = 247). Compared with a daily dose of <1000 mg, the adjusted odds ratios for 1000 to 1500, 1500 to 2000, and ≥2000 mg metformin were 1.72 (P = .080), 3.34 (P < .001), and 8.67 (P < .001), respectively. A total of 22.2% (247 patients) showed vitamin B12 deficiency, with a mean vitamin B12 level of 231.2 ± 44.8 pg/mL(171.25±33.2. pmol/L). In this patient pool, only 1 patient had B12 level <100 pg/mL (74.1 pmol/L), and 60 patients (5.4%) had serum B12 levels <200 pg/ml (148 pmol/L) [20]. There have been several mechanisms proposed that causes B12 deficiency in patients with T2DM on metformin. The mechanisms proposed are; (1) Interference with the calcium-dependent binding of the IF-vitamin B12 complex to the cubilin receptor on enterocytes at the ileum level; (2) Interaction with the cubilinendocytic receptor; (3) Alteration in small intestine motility leading to small intestinal bacterial overgrowth and subsequent inhibition of IF-vitamin B12 complex absorption in the distal ileum; (4) Alteration in bile acid metabolism and reabsorption; (5) Increased liver accumulation of vitamin B12; and (6) Reduced IF secretion by gastric parietal cells[30]. All this has been associated with long term use of metformin. We did not find a significant association between the duration of metformin use and serum levels of B12 (correlation coefficient of -0.12 and with p of 0.36). This again could be due to the small sample size. Another study with findings of low B12 with long duration use of metformin was the study by Vanita et al [27]. In Twenty-seven study centres in the United States participated in their study [27]. Participants were assigned to the placebo group (PLA) (n = 1082) or the metformin group (MET) (n = 1073) for 3.2 years; subjects in the metformin group received open- label metformin for an additional 9 years. Low B12 (≤ 203 pg/mL or 150.4 pmol/L) occurred more often in MET than PLA at 5 years (4.3 vs 2.3%; P = .02) but not at 13 years (7.4 vs 5.4%; P = .12). Combined low and borderline-low B12 (≤ 298 pg/mL or 220.7 pmol/L)) was more common in MET at 5 years (19.1 vs 9.5%; P < .01) and 13 years (20.3 vs 15.6%; P = .02). Years of metformin use were associated with increased risk of B12 deficiency (odds ratio, B12 deficiency/year metformin use, 1.13; 95% confidence interval, 1.06–1.20). Low vitamin B12 was defined as ≤ 203 pg/mL (150.4 pmol/L), and borderline-low levels were defined as between 204 and 298 pg/mL (151.1 and 402 pmol/L) in this study [28]. Similar findings were reported by Malik et al [29]. They reported that patients on prolonged 

Our study showed that higher metformin dosage was significantly associated with low serum B12 values. There was a significant relation between metformin dosage and duration of use on PHQ-9 scores indicating that long duration and higher doses are associated with depression in patients with T2DM. Further studies on the anti-depressant efficacy of metformin as an adjunct to anti-depressants in patients with T2DM must be done as animal models have shown beneficial results.