A team of researchers from the University of Hong Kong (HKUMed) has uncovered a key reason why people with type 2 diabetes (T2D) are more vulnerable to severe viral infections.

Their findings show how high blood sugar (glucose) weakens the immune system, making it harder for the body to fight off viruses.

The study, published in Cell Metabolism, highlights the importance of keeping blood sugar levels in check to improve immunity and overall health.

In Hong Kong, about 1 in 10 adults have T2D, a condition where blood sugar levels remain too high due to issues with insulin, the hormone that regulates glucose.

Even with advances in medications, many patients struggle to control their blood sugar.

Poorly controlled diabetes (PC-T2D) is especially dangerous, as it increases the risk of frequent and severe health problems, including viral infections.

Normally, our immune system defends against viruses by activating special cells called T Helper 1 (Th1) cells.

These cells produce an inflammatory response to destroy infected cells and stop the spread of viruses.

However, during the COVID-19 pandemic, it became clear that T2D patients, especially those with poorly controlled blood sugar, were at much higher risk.

COVID-19 patients with diabetes had a death rate three times higher than those without diabetes, with the greatest risk seen in those with uncontrolled glucose levels.

The HKUMed team, led by Professor Heidi Ling Guangsheng, Dr. Paul Lee Chi-Ho, and Professor Kathryn Tan Choon-Beng, analyzed blood samples from 40 T2D patients.

They found that high blood sugar reduces the effectiveness of Th1 cells by 40% compared to healthy individuals. This weakens the body’s ability to fight off viruses.

The good news? When blood sugar is well-controlled, the immune system can recover. Patients with better glucose control (WC-T2D) showed normal Th1 cell function, highlighting how effective management of diabetes can improve immunity.

Further experiments revealed why high blood sugar weakens Th1 cells. It disrupts the metabolism of CD4+T cells, which are crucial for developing functional Th1 cells.

This disruption leads to the breakdown of a key protein needed for their function, making it harder for the immune system to fight infections. Additionally, high blood sugar can trigger chronic inflammation, further harming immunity and overall health.

This research shows that keeping blood sugar levels stable is not just about preventing diabetes complications like heart disease—it’s also essential for a strong immune system. Well-controlled diabetes reduces the risk of severe symptoms from illnesses like COVID-19, influenza, and other respiratory infections.

To stay healthy, T2D patients should:

• Monitor their blood sugar and know their glycated hemoglobin (HbA1c) levels.
• Take their medications as prescribed.
• Follow a healthy lifestyle, including a balanced diet and regular exercise.

“Managing blood sugar is crucial for protecting against infections and reducing the burden on healthcare systems during pandemics,” said Professor Ling.

By understanding the impact of high blood sugar on immunity, this study paves the way for new treatments to help people with T2D stay healthier and better protected against infections.

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