To date, metformin remains the first-line oral glucose-lowering drug used for the treatment of type 2 diabetes thanks to its well-established long-term safety and efficacy profile. Indeed, metformin is the most widely used oral insulin-sensitizing agent, being prescribed to more than 100 million people worldwide, including patients with prediabetes, insulin resistance, and polycystic ovary syndrome. However, over the last decades several observational studies and meta-analyses have reported a significant association between long-term metformin therapy and an increased prevalence of vitamin B12 deficiency. Of note, evidence suggests that long-term and high-dose metformin therapy impairs vitamin B12 status. Vitamin B12 (also referred to as cobalamin) is a water-soluble vitamin that is mainly obtained from animal-sourced foods. At the cellular level, vitamin B12 acts as a cofactor for enzymes that play a critical role in DNA synthesis and neuroprotection. Thus, vitamin B12 deficiency can lead to a number of clinical consequences that include hematologic abnormalities ( e.g. , megaloblastic anemia and formation of hypersegmented neutrophils), progressive axonal demyelination and peripheral neuropathy. Nevertheless, no definite guidelines are currently available for vitamin B12 deficiency screening in patients on metformin therapy, and vitamin B12 deficiency remains frequently unrecognized in such individuals. Therefore, in this “field of vision” article we propose a list of criteria for a cost-effective vitamin B12 deficiency screening in metformin-treated patients, which could serve as a practical guide for identifying individuals at high risk for this condition. Moreover, we discuss additional relevant topics related to this field, including: (1) The lack of consensus about the exact definition of vitamin B12 deficiency; (2) The definition of reliable biomarkers of vitamin B12 status; (3) Causes of vitamin B12 deficiency other than metformin therapy that should be identified promptly in metformin-treated patients for a proper differential diagnosis; and (4) Potential pathophysiological mechanisms underlying metformin-induced vitamin B12 deficiency. Finally, we briefly review basic concepts related to vitamin B12 supplementation for the treatment of vitamin B12 deficiency, particularly when this condition is induced by metformin.

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Pregnancy is physiologically associated with a gradual increase in insulin resistance, which acts as a physiologic adaptive mechanism to ensure the adequate supply of glucose to the rapidly growing fetus. However, an early adaptive increase in beta-cell glucose sensitivity and beta-cell insulin secretion maintains glucose homeostasis during normal pregnancy. Potential mechanisms behind gestational insulin resistance include hormonal, placental, and genetic or epigenetic factors, as well as the increase in visceral adipose tissue, alterations in gut microbiota, and the concurrent presence of overweight or obesity. In some instances, defects in beta-cell adaptive mechanisms occur, resulting in a substantial exacerbation of insulin resistance and in the possible development of gestational diabetes mellitus (GDM). This chapter aims to provide readers with a basic knowledge of the physiologic adaptations and the possible dysregulations of glucose homeostasis and insulin sensitivity during pregnancy. Indeed, this knowledge is critical to properly identifying women at risk for maternal and/or fetal metabolic complications and tailoring the prevention and treatment strategies for this population. We also briefly discuss the potential factors and molecular/cellular mechanisms accounting for gestational insulin resistance and GDM pathophysiology.

This study was aimed at developing a clinical risk score for cardiovascular autonomic neuropathy (CAN) for type 1 and type 2 diabetes. In a retrospective cross-sectional one-centre study in an unselected population, 115 participants with type 1 diabetes (age 41.1 ± 12.2 years) and 161 with type 2 diabetes (age 63.1 ± 8.9 years), wellcharacterized for clinical variables, underwent standard cardiovascular reflex tests (CARTs). Strength of associations of confirmed CAN (based on 2 abnormal CARTs) with clinical variables was used to build a CAN risk score. CAN risk score was based on resting heart rate, HbA1c, retinopathy, nephropathy, cardiovascular disease in both type 1 and type 2 diabetes, and on HDL cholesterol, systolic blood pressure, and smoking in type 1 diabetes or insulin treatment and physical activity in type 2 diabetes (range 0-10). In type 1 diabetes, CAN risk score showed an area under the ROC curve (AUC) of 0.890 ± 0.034, and at cut-off of 4 sensitivity of 88%, specificity of 74.4%, and negative predictive value (NPV) of 95.7% for confirmed CAN. In type 2 diabetes, CAN risk score showed an AUC of 0.830 ± 0.051 and at the cut-off of 4 sensitivity and specificity of 78.6% and 73.5%, respectively, and NPV of 97.3% for confirmed CAN. These newly developed CAN risk scores are accessible in clinical practice and, if confirmed in a validation study, they might identify asymptomatic individuals with diabetes at greater risk of CAN to be referred to CARTs, thus limiting the burden of a universal screening.

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