Damage to kidneys and eyes may start before people are diagnosed with diabetes

One in two people diagnosed with type 2 diabetes already have damage to their eyes, kidneys or heart. That damage is more likely if they had problems with blood sugar control before being diagnosed.

Diabetes causes damage to blood vessels, because of poorly-controlled levels of sugar in the blood. These damaged blood vessels can lead to heart disease, stroke, kidney disease or eye disease.

Problems with blood sugar control are sometimes called ‘pre-diabetes’ if they do not reach the level at which doctors diagnose diabetes. People who have pre-diabetes may be advised to change their diet and lifestyle to try to prevent diabetes. But less is known about how much damage is done to blood vessels by pre-diabetes.

This study found that people with pre-diabetes in the three years before being diagnosed with diabetes were more likely to have damaged blood vessels than those with a record of normal blood sugar. The results suggest that offering treatment while people are still in the pre-diabetes phase might help prevent this damage. However, more research is needed to be certain.

What’s the issue?

Type 2 diabetes is common and increasing. Almost 4 million people in the UK have been diagnosed with diabetes, and 90% of these have type 2 diabetes. An estimated 1 million people have diabetes but are undiagnosed.

By the time people are diagnosed, they may already have damaged blood vessels. Damage to large blood vessels (known as macrovascular complications) can cause heart disease and stroke. Damage to small blood vessels (microvascular complications) can cause kidney and eye disease.

Blood tests can identify people whose blood sugar is not properly controlled, but who do not meet the threshold for being diagnosed with diabetes. It is not clear how important this ‘pre-diabetes’ condition is.

The researchers wanted to find out whether people who had pre-diabetes before their diabetes diagnosis were more likely to have heart, kidney or eye disease. They hope that early treatment of pre-diabetes might prevent some of these diseases.

What’s new?

Researchers used a UK database to find everyone who was diagnosed with diabetes between 2004 and 2017. This amounted to 159,736 people.

Almost half had at least one of heart disease, stroke, kidney disease or eye disease at the time they were diagnosed with diabetes. People with pre-diabetes were more likely to have these conditions than people with previous records of normal blood sugar.

The researchers found:

  • two fifths of people had a record of a blood sugar test in the 3 years before their diagnosis
  • two thirds of these people had pre-diabetes and one third had normal blood sugar
  • one quarter of those with pre-diabetes had eye disease, kidney disease or heart disease at the time of diagnosis
  • people with a normal blood sugar record were much less likely to have these conditions at time of diagnosis

After taking other factors into account, the researchers calculate that people with pre-diabetes were 75% more likely to have eye disease than people who had normal blood sugar before their diabetes diagnosis.

Why is this important?

The results show that people who had pre-diabetes in the three years before their diabetes diagnosis were more likely to have damage to their eyes, kidneys or heart by the time they were diagnosed.

It may be that doctors could offer treatment or lifestyle advice sooner to people with pre-diabetes, to help them avoid this damage. However, this research is not sufficient to tell us whether that would work.

What’s next?

The research gives a snapshot of the three years before a diagnosis of diabetes. It does not show how diseases of the kidney, eye and heart develop over time. For example, it does not show whether these diseases developed before or after pre-diabetes, and whether they got worse as blood sugar control worsened. More research over time would help doctors decide when best to offer treatment.

Further research might help in the design of treatments to reduce damage to eyes, kidneys and heart at an earlier stage. Treatments could be tailored to the patients’ individual risks before a diagnosis of diabetes.

You may be interested to read

The full paper: Palladino R and others. Association between pre-diabetes and microvascular and macrovascular disease in newly diagnosed type 2 diabetes. BMJ Open Diab Res Care 2020; 8: e001061

Ali M, and others. Cardiovascular and renal burdens of prediabetes in the USA: analysis of data from serial cross-sectional surveys, 1988–2014. Lancet Diabetes & Endocrinol. 2018;6:P392-403

Fagg J & Valabhji J. How do we identify people at high risk of Type 2 diabetes and help prevent the condition from developing? Diabet Med. 2019;36:316-325

The Diabetes UK website gives an overview of information about diabetes and vascular complications.



This research was supported by NW London NIHR Applied Research Collaboration and NIHR Applied Research Collaboration East Midlands.



Study author

This research might prompt doctors to carry out much more thorough assessments of patients diagnosed with pre-diabetes. The research suggests that patients with pre-diabetes should be checked for signs of damage to eyes, kidneys and heart. They may need individualised strategies to reduce their risk of damage to blood vessels and serious complications later on. This would involve a broader assessment of people’s vascular risk, including body mass index, blood pressure and overall lifestyle.

Type 2 diabetes is placing an increasing burden on health systems as the number of patients continues to rise. The public, patients, professionals and policy makers all need to know about this research.

Raffaele Palladino, Research Associate, School of Public Health, Imperial College London

Clinician scientist 

The results clearly show that we should change our thinking. Diabetes management should be offered along a continuum from normal blood sugar, to pre-diabetes to type 2 diabetes. At present, care is suddenly provided when a patient’s glucose levels goes above the threshold for diabetes, while we need to aim to intervene and prevent vascular disease probably from the pre-diabetes stage by addressing the vascular risk factors such as obesity, hypertension, hyperlipdaemia and smoking among others. The NHS Diabetes Prevention Programme is a step in the right direction.

Ideally, we need interventional studies showing that intervening in the pre-diabetes stage can reduce vascular complications, even if diabetes does develop.

Abd Tahrani, Senior Lecturer in Metabolic Endocrinology and Obesity Medicine, University of Birmingham, and Honorary Consultant Endocrinologist and Bariatric Physician, University Hospitals  Birmingham NHS Foundation Trust

Conflicts of Interest

None declared.