Eating too much salt seems to impair body’s ability to fight bacteria

By Michael Le Page

Eating too much salt may impair the body’s ability to fight bacterial infections, according to studies in mice and in 10 human volunteers.

Christian Kurts at the University Hospital of Bonn in Germany and his team first showed that mice given a high salt diet were less able to fight kidney infections caused by E. coli and body-wide infections caused by Listeria monocytogenes, a common cause of food poisoning.

“The bacteria caused more damage before the immune system got rid them,” says Kurts.

Next, the team gave 10 healthy women and men who were 20 to 50 years old an extra 6 grams of salt a day on top of their normal diet, in the form of three tablets a day. After a week, some of their immune cells, called neutrophils, had a greatly impaired ability to engulf and kill bacteria compared with the same tests done on each individual before they took extra salt.

The team didn’t examine the effect of high salt intake on the body’s ability to fight viral infections.

The World Health Organization recommends that people eat no more than 5 grams of salt a day to avoid high blood pressure, which can cause strokes and heart disease. In the UK, people eat 8 grams on average, suggesting many consume as much or more than the volunteers in the study.

The team thinks two mechanisms are involved. First, when we eat lots of salt, hormones are released to make the body excrete more salt. These include glucocorticoids that have the side effect of suppressing the immune system throughout the body.

Second, there is a local effect in the kidney. Kurts found that urea accumulates in the kidney when salt levels are high, and that urea suppresses neutrophils.

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.aay3850

https://www.newscientist.com/article/2238629-eating-too-much-salt-seems-to-impair-bodys-ability-to-fight-bacteria/?utm_source=NSDAY&utm_campaign=8ea0a51a66-EMAIL_CAMPAIGN_2020_03_25_04_56&utm_medium=email&utm_term=0_1254aaab7a-8ea0a51a66-374123611

The behavioral immune system curbs human dating

Activating something called the behavioral immune system puts a damper on dating, new research shows.

About a decade ago, evolutionary psychologists suggested that humans have evolved a first line of defense against disease: this behavioral immune system or BIS.

The theory is that perceiving, rightly or wrongly, the threat of disease unconsciously activates this system. Although we cannot see microorganisms with the naked eye, we are nevertheless able to identify cues—such as coughs, unpleasant smells, or skin lesions—that hint at the possible presence of pathogens, whether or not these are actually present or represent real health threats.

Scientists have suggested that the activation of the BIS leads to prejudiced and avoidant attitudes and behavior towards those who display superficial cues connoting disease.

But how does this affect our dating lives, where two competing needs are pitted against one another—i.e., the potential benefits of connecting and finding a mate versus the need to protect oneself from disease? McGill University scientists set out to find out, by looking at the activation of the BIS in young, single, heterosexual Montrealers in both real speed-dating events and in experimental online dating.

The results were convincing. And not very happy.

“We found that when the behavioral immune system was activated it seemed to put the brakes on our drive to connect with our peers socially,” says first author of the study Natsumi Sawada, who holds a PhD in psychology from McGill University.

“We hadn’t expected this to be the case in real life situations like dating where people are generally so motivated to connect. The results suggest that beyond how we consciously or unconsciously think and feel about each other there are additional factors that we may not be consciously aware of, such as a fear of disease that may influence how we connect with others.”

This video explains how the experiments worked:

The findings appear in the Personality and Social Psychology Bulletin. The Social Sciences and Humanities Research Council (SSHRC) and the Fonds de Recherche sur la Société et la Culture (FRQSC) supported the work.

This other immune system can crimp your love life