Does metformin treatment reduce cancer-associated mortality in type 2 diabetes mellitus (DM), is there an association between type 2 diabetes mellitus and postoperative pneumonia, and how does diabetes affect morbidity and mortality in COVID-19?

Updated: Jul 28, 2020
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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In a meta-analysis of 20 publications comprising 13,008 cancer patients with concurrent type 2 diabetes, researchers found that patients treated with metformin had better overall and cancer-specific survival than those treated with other types of glucose-lowering agents. [102, 103] These improvements were observed across cancer subtypes and geographic locations. Risk reduction was significant among patients with prostate, pancreatic, breast, colorectal and other cancers, but not for those with lung cancer. However, it remains unclear whether metformin can modulate clinical outcomes in cancer patients with diabetes.

A study by López-de-Andrés et al found the incidence of postoperative pneumonia in patients with type 2 diabetes to be 21% higher than in nondiabetic patients, although the risk of inhospital mortality following the development of postoperative pneumonia was no greater in the presence of type 2 diabetes. [104]


A retrospective study by Chen et al of 136 COVID-19 patients with diabetes (primarily type 2 diabetes) found that older age, elevated C-reactive protein, and insulin use were risk factors for mortality. The adjusted odds ratio (OR) for mortality in insulin use was 3.58. It has been questioned, however, whether insulin itself is a risk factor or if the increased mortality reflected the characteristics of the patients taking it. [105, 106]

A study by Bode et al indicated that among patients with COVID-19, the US in-hospital death rate for individuals living with diabetes, patients with an HbA1c of 6.5% or higher, and those with hyperglycemia throughout their stay is 29%, a figure over four times greater than that for patients without diabetes or hyperglycemia. Moreover, the in-hospital death rate for patients with no evidence of preadmission diabetes who develop hyperglycemia while admitted was found to be seven times higher (42%). [107, 108]

A retrospective study by Zhu et al found that among individuals with COVID-19, those who also had type 2 diabetes mellitus had a mortality rate of 7.8% (versus 2.7% for those without diabetes), as well as a higher rate of multiple organ injury. However, the investigators also reported that among the patients with type 2 diabetes, the mortality rate was lower in those who, during hospitalization, had well-controlled blood glucose, that is, patients with a glycemic variability within 3.9 to 10.0 mmol/L, than in those with poorly controlled blood glucose, in which the upper limit of glycemic variability extended beyond 10.0 mmol/L. [109, 110]

A retrospective study by Wang et al indicated that hyperglycemia, even in the absence of diabetes, is an independent predictor of 28-day mortality in patients with COVID-19. The investigators reported that on admission to two hospitals in Wuhan, China, 29.1% of study patients with COVID-19 and no prior diagnosis of diabetes had a fasting blood glucose of at least 7.0 mmol/L. It was believed that the individuals with hyperglycemia included not only persons with undiagnosed diabetes, but also nondiabetic patients with acute stress hyperglycemia. With regard to 28-day mortality, it was determined that the hazard ratio in patients with a fasting blood glucose of 7.0 mmol/L or higher was 2.30. [111, 112]

A study by Sardu et al indicated that in hospitalized patients with COVID-19 and moderately severe pneumonia, those with diabetes and those who are hyperglycemic are at higher risk of severe disease than are normoglycemic patients without diabetes. Moreover, among the patients in the study with hyperglycemia, the risk of severe disease was lower in those who were treated with insulin infusion, providing further evidence of the importance of in-hospital glucose control. [106, 113]

A study by Cariou et al reported that in patients with diabetes hospitalized for COVID-19, a positive, independent association was found between higher body mass index (BMI) and risk of tracheal intubation and/or death within 7 days. The median BMI in patients who suffered this outcome was 29.1 kg/m2, compared with 28.1 kg/m2 in those who did not. However, an association was not found between long-term glucose control and 7-day tracheal intubation and/or death. Regarding specific outcome rates, the study, in which 88.5% of the diabetes cases were type 2 diabetes, reported that 20.3% of the patients with diabetes who were hospitalized with COVID-19 underwent tracheal intubation within 7 days, while 10.6% died within this time. [114, 115]

The Centers for Disease Control and Prevention (CDC) includes type 2 diabetes in the list of conditions that increase the likelihood of severe illness in persons with COVID-19, and type 1 diabetes in the list of conditions that may increase this likelihood. [116]

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