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24th August 2021
A refractive error represents a common eye disorder that prevents the eye from being able to focus images properly leading to blurred vision. There are several types of high refractive errors (HRE) including myopia (near-sightedness), hyperopia (far-sightedness), astigmatism (distorted vision) and presbyopia (difficulty in reading at arm’s length). The World Health Organisation has estimated that 153 million people worldwide have a visual impairment due to HRE. In children, the most common error is astigmatism, with one study finding a global prevalence of 14.9%. The cause of HRE remains uncertain although refractive changes are known to be associated changes in blood glucose levels and hence can be present in those with diabetes. In fact, there is some evidence that gestational diabetes can result in a three-fold increased probability of refractive errors compared to mothers without diabetes. In contrast, another study of refractive errors among diabetic and non-diabetic mothers found no significant differences in astigmatism between the two groups.
With some uncertainty over the relationship between HRE errors and diabetes, a team led by researchers from the Department of Clinical Epidemiology, Aarhus University, Denmark, undertook a population-based cohort study using Danish national registers. Mothers were considered to have diabetes if they were diagnosed either before or during their pregnancy. Their primary outcome of interest was high refractive errors in offspring and secondary outcomes were the specific types of refractive errors that developed over a 25-year follow-up period. The team used regression analysis to model the association between prenatal diabetes exposure and high refractive errors, adjusting for several factors including maternal age, smoking status, calendar period of delivery.
During the 25-year follow-up, there were 553 children of mothers with diabetes and 19,695 children of mothers without diabetes, diagnosed with a HRE. The children exposed to maternal had a 39% increased risk of having a HRE compared to those without diabetes (adjusted hazard ratio, aHR = 1.39, 95% CI 1.28 – 1.51, p < 0.001). This risk was significantly increased, compared to mothers without diabetes, for all forms of pre-gestational diabetes e.g., type 1 (aHR = 1.32), type 2 (aHR = 1.68) and gestational diabetes (aHR = 1.37). The risks for each type of HRE were also increased, e.g., hypermetropia (HR = 1.37), myopia (HR = 1.34) and astigmatism (HR = 1.58). In addition, the risks of HRE were higher in children of mothers who had at least one diabetic complications (aHR = 1.76) and higher still, in the presence of two or more complications (aHR = 2.24).
In trying to account for these elevated risks, the authors suggested the among diabetic mothers, it was possible that increased plasma glucose levels could result in foetal hyperglycaemia or that an increased oxidative stress and inflammatory response from the ensuing hyperglycaemia could have damaged the optical nerves. They concluded that given these finding, early ophthalmological screening should be undertaken in the children of mothers with diabetes.
Du J et al. Association of maternal diabetes during pregnancy with high refractive error in offspring: a nationwide population-based cohort study. Diabetologia 2021
18th January 2021
It has become recognised that increasing age and a higher number of co-morbidities such as hypertension, obesity and diabetes are associated with higher levels of mortality among those infected with COVID-19.
Given that the prevalence of diabetes is often very high among this ethnic group, a team from the Hugh Kaul Precision Medicine Institute, University of Alabama, US, sought to determine the effects of different anti-diabetic treatments on mortality among an ethnically diverse population infected with COVID-19. The team retrospectively reviewed all electronic health records of subjects consecutively tested for COVID-19 between February and June 2020 at a single tertiary hospital in their area. In an effort to make the results more generalisable, the researchers included all patients within the five month period with the only exclusion criterion being a lack of available outcome data. The team sought to focus their attention on the diabetic treatments and in particular, insulin and metformin because these were the most commonly prescribed and there were too few patients prescribed other medicines to provide a meaningful statistical analysis. The primary outcome for the study was overall mortality and the researchers used logistic regression to explore the association between mortality and known risk factors and diabetic treatments.
There were 604 patients who tested positive for COVID-19 during the study period. The majority of those testing positive (43%) were aged 50 to 70 years and just over half (51.5%) were Black Africans, giving a highly significant odds of testing positive compared to those of white ethnicity (odds ratio, OR = 2.6 95% CI 2.19–3.10, p < 0.001). Overall mortality among those testing positive for COVID-19 was 11% and the presence of diabetes dramatically increased the risk of mortality (OR = 3.62 95% CI 2.11–6.2, p < 0.001). In fact, 67% of all deaths occurred among those with diabetes. Focusing on diabetic treatments, the researchers observed that use of metformin reduced the odds of dying by 62% (OR = 0.38 95% CI 0.17–0.87, p = 0.0221) although no such effect was seen with insulin. Moreover, after adjusting for the covariates age, race, sex, obesity and hypertension status, the odds ratio remained significant (OR = 0.33 95% CI 0.13–0.84, p = 0.0210). The researchers also observed that neither BMI or HBA1C levels were lower in those taking metformin thus discounting these as explanatory factors.
The authors noted that while the presence of type 2 diabetes was associated with an increased mortality risk in those with COVID-19 (as reported in other studies) there appeared to be a protective effect among diabetic patients treated with metformin although they were unable to explain their findings and called for more research to understand how metformin conferred these effects.
Crouse AB et al. Metformin use is associated with reduced mortality in a diverse population with COVID-19 and diabetes. Front Endocrinol 2021.