Eating Too Much Salt Could Cause Stress Levels to Rise

There’s a reason why your Christmas dinner tastes so good—the turkey, gravy, potatoes, and trimmings make up one of the saltiest meals you’re likely to consume all year. Add to that the crisps, cheeses, and other snacks that we like to tuck into over the holiday period, and our salt levels across the festive season can end up far beyond what’s needed or recommended.

The physical effects of this are well known. As salt levels rise, so does blood pressure, which can increase the risk of a heart attack or stroke. But scientists think that salt could also have another influence: on behavior. In particular, they’re beginning to unpick how it’s linked to stress. 

The topic has, until recently, been underexplored, as the impact of salt is a difficult subject to examine in humans. Monitoring people’s salt intake, even under controlled conditions, is hard because of how ubiquitous it is in our food. Plus, since salt can increase blood pressure acutely and over time, knowingly adding salt to the diet of study participants poses an ethical problem. 

So researchers at the University of Edinburgh have been running experiments with the next best thing: mice. They’re very similar to humans in terms of anatomy, physiology, and genetics—and how both species respond to stress is governed by factors that can include diet, explains Matthew Bailey, a professor of renal physiology at the university. Mice also typically don’t eat a lot of salt, which makes testing its impact on them easier.

To investigate the link between salt intake and stress, Bailey and his colleagues fed male mice—some for two weeks, some for up to eight weeks—a high-salt diet, containing a proportion of salt similar to the typical intake of humans. When the researchers then analyzed blood samples from the mice, they found that levels of the stress hormone cortisol were always higher in those on the high-salt diet compared to mice in the control group consuming low levels of salt—both when they were in a resting state and after being restrained in a Plexiglas tube to induce stress. The stress response wasn’t turned on and off by adding salt to the mice’s diet, but amplified, Bailey explains. “It’s like a dimmer switch in a light,” he says. “The stress system was kind of turned on a little bit more.”

How the different stressors—the salt in the mice’s body and the stressful Plexiglas environment—affect each other and compound is particularly interesting, Bailey continues, because humans are also often exposed to multiple stressors at once. So it’s possible that something similar could be happening in our own bodies. Just think of the last-minute gifting spree or heated debates at the dinner table at Christmas with annoying relatives, which send people’s blood pressure soaring—and then add to this the overindulgence in salty food over the festive season. “I think that for some people, the diet that we’re eating is going to make us deal with it less well than we would otherwise,” says Bailey.