Smoking increases the risk of infection, even among otherwise healthy people

Diet and lifestyle 20. jun 2023 3 min Research Assistant Bertram Dalskov Kjerulff Written by Morten Busch

Tobacco kills millions of people every year through respiratory tract and cardiovascular diseases. Nevertheless, knowledge is lacking about the short-term effects of smoking. New research on how smoking is associated with infections among healthy blood donors shows that more smokers than nonsmokers require hospital treatment because of infections. Smokers also have a much higher incidence of respiratory tract infections, abscesses and skin infection, even among young smokers. The researchers hope that knowing about these acute effects can get young people in particular to quit smoking.

Some young people can have difficulty imagining what might happen in 30–40 years. Many young people want to live in the fast lane, and for many, smoking addiction starts at a young age, with long-term harmful effects on the heart, blood vessels and lungs emerging later in life. However, new research suggests that both young and older smokers should also consider more of the short-term effects of smoking before lighting the next cigarette.

“Our study adds acute infections to the growing list of harmful effects of smoking, even among otherwise healthy individuals. We found a marked increased risk of hospital treatment for most types of infection and increased prescription of antimicrobial medicines. Somewhat surprisingly, we also found that smoking strongly affects skin health: infections and especially abscesses,” explains Bertram Dalskov Kjerulff, Research Assistant, Department of Clinical Immunology, Aarhus University Hospital.

What about skin?

The background for the project was that the researchers had noticed a lack of knowledge about the effects of smoking that might lead to underestimating the dangers: more specifically, the frequency and severity of infections. Most previous studies focused on people seeking healthcare because of infectious diseases or examined mortality from infections in the general population.

“Our study investigated the association between smoking and the risk of infections among otherwise healthy people. By conducting a very large study with healthy blood donors, we hoped to determine whether smoking directly increases the risk of infections, even among people who did not already have another disease,” says Bertram Dalskov Kjerulff.

The study used questionnaire and health registry data from 127,831 blood donors from the Danish Blood Donor Study, the Danish National Prescription Registry and the Danish National Patient Registry. The blood donors’ information, including their history of hospitalisation and filled prescriptions, was linked to information on smoking habits, enabling the researchers to estimate how smoking is associated with the risk of various infections.

“We hypothesised that smoking would be associated with an increased risk of infection based on the known effects of smoking on the immune response, but we wanted to determine how great the effect was and whether it differed between organ systems. The respiratory tract was the most obvious system, but we wanted to determine the effects on the skin, the gastrointestinal tract, and the urinary tract, since smoking has well-known systemic effects,” says Bertram Dalskov Kjerulff.

Sign of a stressed body

The results were very pronounced. Smokers had a higher risk of infection of all types than nonsmokers, and the risk of hospital treatment for infections was 27% higher among male smokers and 33% higher among female smokers. The risk of being prescribed an antimicrobial medicine was 11% higher among male smokers and 20% higher among female smokers. Smoking was especially strongly associated with being prescribed broad-spectrum penicillin.

“The exact mechanisms behind these results are not yet known, but blood donors are generally healthy and therefore suitable for assessing how smoking alone affects the risk of infection. Smokers might generally have a riskier lifestyle, thereby also exposing them to more potential infections, but the evidence indicates that smoking leads to an increased risk of infection and increased use of antimicrobial medicine in this large group of otherwise healthy people,” explains Bertram Dalskov Kjerulff.

Previous research indicates that smoking can affect both the innate and acquired immune systems, leading to structural changes that enable microorganisms to penetrate and infect the body more easily, even though smokers’ immune systems are often overactivated by the hot smoke and its many chemicals.

“Unfortunately, a very active immune system does not necessarily mean a very effective immune system. This is more a sign of a stressed body with constant inflammation, and the immune response may aim for the wrong targets. Our studies indicate a smoking-related increase in the risk of many types of infections, not just in the lungs but, surprisingly, a more than 100% increase in the risk of abscesses and generally higher risk of bacterial infections in the skin, muscles and connective tissue such as ligaments and tendons,” says Bertram Dalskov Kjerulff.

Could be a decisive argument

Staphylococcus aureus probably causes most of the infections, which is in accordance with the infections being associated with prescriptions for antibiotics such as dicloxacillin and flucloxacillin.

“Smoking is also known to increase the risk of wound infection after surgery, and smokers have impaired wound healing, so these changes in immunity are not limited to the respiratory tract at all, which may explain the overall increased risk of infection,” explains Bertram Dalskov Kjerulff.

The new research thus once again emphasises that smoking imposes great costs on healthcare systems worldwide and impairs smokers’ quality of life. Since the researchers especially focus on young people’s smoking habits and their effects, they have now begun to examine the effects of smokeless tobacco products and passive smoking, to investigate what is causing the huge increase in infections.

“This information is crucial for everyone, but especially for teenagers who may be experimenting with smoking, since this emphasises how smoking adversely affects skin health and wound healing – both in the long and short term. By understanding these risks, we can help to educate teenagers about the harmful effects of smoking and perhaps provide a decisive argument so they do not start smoking,” concludes Bertram Dalskov Kjerulff.

Smoking is associated with infection risk in healthy blood donors” has been published in Clinical Microbiology and Infection. The project received funding from a Novo Nordisk Foundation Challenge Programme grant for BERTHA – the Danish Big Data Centre for Environment and Health in which the Danish Blood Donor Study is a collaborating partner.

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