It is not new that being overweight and obese is harmful to health. So far, this has primarily referred to diseases of civilization such as diabetes, high blood pressure and cardiovascular diseases. Two large long-term studies have now shown that being overweight also increases the risk of infections and severe courses of such diseases. People with obesity have a 70 percent higher risk of being hospitalized or dying from an infection. With a body mass index of over 40, the risk is three times higher than for people of normal weight. According to the analyses, one in ten deaths from an infectious disease could be due to obesity – regardless of the comorbidities caused by excess weight.
More and more people around the world are obese – their body mass index (BMI) is more than 30. Here in Germany, obesity is no longer a marginal phenomenon, almost a quarter of the population is very overweight, and more than half of women and men have a BMI of over 35. And the frequency of obesity has also been increasing among younger people in recent years. Many consequences of such a greatly increased body fat percentage are already known. “Obesity is a known risk factor for metabolic syndrome, diabetes, cardiovascular disease and many other chronic conditions,” explains senior author Mika Kivimaki from University College London. Studies show that some types of cancer are also promoted by being overweight. There is also evidence that an extremely high body fat percentage also limits some immune functions.
Up to three times increased risk
Kivimaki, lead author Solja Nyberg from the University of Helsinki and their colleagues have now investigated for the first time in more detail whether there is a connection between obesity and severe infectious diseases. For their study, they evaluated data from 67,000 participants in a Finnish cohort study and from more than 470,000 participants in the British Biobank long-term study. All test subjects were middle-aged and were examined for body mass index and health status at the beginning and throughout the studies. Their medical career was followed for an average of 13 to 14 years, so information about infections and their course can also be found in this data. For a total of 925 bacterial, viral or fungal pathogens, Nyberg and his colleagues evaluated whether there was a difference between normal-weight or obese study participants in terms of infection frequency and severity.
The evaluations showed that people who are very overweight suffer from infections more often and more severely than those of normal weight. “With few exceptions, there was a clear dose-response relationship between different levels of obesity and the risk of serious infections,” report Nyberg and his team. Specifically, it was shown that people with a BMI over 30 have a 70 percent higher risk of being hospitalized or dying from an infection. In people with extreme obesity and a BMI of more than 40, the risk of severe disease was three times higher, the researchers found. “This association between obesity and severe infections remained even when we took other risk factors into account,” explains the team. Accordingly, the increased susceptibility to infections is not related to the fact that obese people often have previous illnesses such as diabetes, metabolic syndrome or cardiovascular diseases – the increased risk of infection is independent of this.
Responsible for one in ten infection-related deaths worldwide
Overall, the data suggests that one in ten deaths from infections worldwide are caused by obesity and are potentially preventable. During the Covid19 pandemic, this proportion rose to 15 percent, as the researchers report. However, there are regional differences: in countries where a particularly large number of people are very overweight, the proportion is significantly higher. In the USA, a good quarter of all infection-related deaths can be attributed to obesity; in Germany it is 14.7 percent. “We now have robust evidence that people with obesity are more likely to get infections and that this has more severe consequences for them,” says Kivimaki. This connection was also confirmed when the team analyzed ten common infectious diseases in more detail, including influenza, Covid-19, pneumonia, gastroenteritis, bladder infections, HIV and tuberculosis. With the exception of the last two, it was also shown that people with obesity have to be treated in hospital for these infections or die from them more often than people of normal weight.
The researchers believe that a possible reason for the increased susceptibility of very overweight people to infections is a disruption of important immune functions. “Our results suggest that obesity weakens the body’s defense against infections, which makes these diseases worse,” explains Kivimaki. “Those affected do not necessarily become infected more often, but the effects of the infection are more serious for them.” According to the research team, this underlines the urgent need to stop the global increase in obesity. “If obesity rates continue to rise worldwide as predicted, then there will also be more and more hospitalizations and deaths from infectious diseases,” says Nyberg. “We therefore urgently needed measures to help people lose weight and stay healthy.” It is also important for people with obesity to have the recommended vaccinations administered.
Source: Solja Nyberg (University of Helsinki) et al., The Lancet, doi: 10.1016/S0140-6736(25)02474-2