Too much salt and too little exercise is hard on the heart, but new research suggests it can be hard on the brain, too. A three-year study of more than 1,200 people has linked a salty diet and sedentary lifestyle to cognitive decline in old age.
"It's important for people to know there are things you can do to help protect your brains as you're aging," said study author Carol Greenwood, a nutrition scientist and interim director of the Baycrest Kunin-Lunenfeld Applied and Evaluative Research in Toronto. "You do have some control, and lifestyle is key."
Using data from the Longitudinal Study on Nutrition and Successful Aging, a study of people between the ages of 67 and 84, Greenwood and colleagues found that men and women with the highest daily sodium intake and the lowest level of exercise performed poorer over time on cognitive tests than those with low sodium intake and an active lifestyle. The findings held up even when the researchers controlled for such factors as education, waist circumference, diabetes and overall diet.
"This is the first study to extend the benefits of low sodium intake to brain health in healthy older adults," the authors wrote in their report published in the Neurobiology of Aging.
The study adds to mounting evidence that too much salt can have serious health consequences.
"The reality is that excess sodium affects not only blood pressure but bone health, and probably cardiac health overall," said Dr. David Katz, director of Medical Studies in Public Health at Yale University. "And further, it tends to be a marker of an overly processed diet that is itself harmful in a variety of ways."
Replacing processed foods that are naturally high in salt with natural foods such as fruits and vegetables is an easy way to lower salt intake.
Studies are increasingly supporting a role for blood vessel damage in dementia. And although sodium can cause a risky rise in blood pressure, salt's sinister association with cognitive functioning was seen in people with and without hypertension.
Although cutting down on salt is a safe move, staying fit might be the more important factor when it comes to protecting cognition with age.
"People who were physically active were protected, regardless of their sodium intake," said Greenwood. "What's important is maintaining the integrity of the cardiovascular system, and the benefits of exercise are going to outweigh any negative effects we see with salt."
People who were sedentary but had look salt intake showed no cognitive decline over three years, the researchers found.
Katz said health-promoting behaviors, like exercise, can "immunize" people to some degree against bad behaviors that inevitably creep in from time to time.
"It stands to reason that people who are more active, and fitter, and thus healthier overall, would better 'withstand' the potential harms of excess sodium than those lacking this immunizing benefit," he said.
Katz cautioned that the study is observational, and does not mean that salt causes cognitive decline. However, the takeaway messages ring true, he said.
"Whether or not dietary sodium directly affects cognitive function in older people, its intake should be restricted to recommended levels, best achieved by eating fewer processed foods, and more foods direct from nature."