We talked a lot about
obesity during the Covid-19 pandemic, often as a risk factor for serious forms. A new international study shows that the phenomenon goes far beyond the coronavirus. By following hundreds of thousands of adults for more than ten years, researchers explored the link between excess weight and severe infections. The results give another dimension to the problem.
An individual risk of serious form which increases with BMI
Published in the medical journal The Lancetthe study analyzed data from more than 540,000 people in Finland and the United Kingdom. Their body mass index (BMI) was measured at baseline, then each participant was followed for 13 to 14 years via hospitalization and death records.
In obese people (BMI ≥30 kg/m²), the risk of being hospitalized or dying from an infection was 70% higher than that of adults of so-called healthy weight (BMI 18.5–24.9). When the BMI exceeded 40 kg/m² (morbid obesity), the risk of severe disease was approximately three times higher. This gradient was observed for most of the infections studied, from influenza to Covid-19 including pneumonia and urinary infections.
This increased risk appeared even in participants without diabetes or heart disease, which argues for a direct role of obesity. Weight loss also counted: leaving obesity to return to overweight or healthy weight was accompanied by around 20% fewer serious forms, while going from overweight to obesity added 30% risk. For Mika Kivimäki of University College London, these results are consistent with the idea of a weakening of immune defenses:
“Obesity appears to weaken the immune system’s ability to deal with infections, increasing the risk of severe forms of the disease..
He also mentions that experimental research on weight loss drugs indicates a connection with the immune system, with decreasing obesity appearing to reduce the risk of severe infections, as well as providing other health benefits. However, Mika Kivimäki underlines the importance of continuing studies to validate the mechanisms that explain these relationships.
One in ten deaths worldwide linked to obesity
By combining these individual risks with global statistics, the authors estimated the share of infectious deaths linked to obesity. In 2023, the team estimates that around 0.6 million out of 5.4 million deaths due to
infectious diseases were associated with obesity, i.e. 10.8%, almost one in ten deaths
in the world.
In the Nordic countries, researchers estimate that the share of deaths from infectious diseases associated with obesity is for the Finland: 19%; for Sweden: 13%; for Norway: 11% and for Denmark: 12%. In 2023, the United States recorded the largest share among high-income countries at 26%.
For the first author, these figures are not trivial: “Our findings suggest that people living with obesity are significantly more likely to become seriously ill or die from a wide range of infectious diseases. As obesity rates are expected to increase globally, the number of deaths and hospitalizations from obesity-related infectious diseases will also increase. summarized Solja Nyberg, from the University of Helsinki.
Vaccines, weight loss: how to limit this risk of infection
Without asserting a cause and effect link, the authors believe that these results call for reinforced prevention in obese adults. They point out that weight loss goes hand in hand with fewer serious infections and emphasize the importance of vaccines. Concretely, they recommend that people living with obesity pay particular attention to:
- Update their recommended vaccinations and accept boosters offered to at-risk groups;
- Discuss weight management options with their doctor, including nutritional monitoring and appropriate physical activity.
The authors emphasize that their work, purely observational and carried out mainly in Europe, does not prove causality, and that global estimates remain approximate.