Cutting back on sodium might help older adults maintain their cognitive function, particularly in those who aren't physically active.
In a study of more than 1200 older adults with normal cognitive function at the outset, researchers found that a high intake of sodium combined with low levels of physical activity was associated with a decline in global cognitive function over 3 years. "Importantly, this association was independent of hypertension and global diet quality," the researchers say. "The independent effect of sodium intake from other nutrient intakes, including energy and lipids, suggests that sodium intake alone may affect cognitive function in sedentary older adults above and beyond the effects of overall diet," they note.

The study is published online August 19 in the Neurobiology of Aging.

The well-established negative impact that high sodium intake has on cardiovascular health has led to the development of worldwide population salt-reduction strategies. Given the link between cardiovascular factors, such as hypertension, and brain health, Dr. Fiocco's team wanted to examine the effects of sodium intake on cognitive function.

After controlling for age, sex, education, waist circumference, diabetes, and overall diet, there was an association between sodium intake and cognitive change over time in those with low levels of physical activity. In the low physical activity group, those with low sodium intake displayed better cognitive performance over time than those with medium and high levels of sodium intake. The findings remained unchanged after additional adjustment for intakes of energy, calcium, cholesterol, and total lipids, and total Canadian Healthy Eating Index score, the researchers say.

They failed to see an association between sodium intake and cognitive health among the highly physically active adults. "One potential explanation for this finding is that the impact of physical activity outweighs the impact of sodium intake on cognitive function, making it more difficult to find an association," Dr. Fiocco said.

Dr. Fiocco and colleagues say it is important to note that people who experienced a decline in global cognitive function over the study period "displayed normal age-related decline and did not display clinically significant rates of decline."
According to previous research, a potential mechanism underlying the association between sodium intake and cognition is blood pressure levels, which are associated with white matter lesions observed in dementia patients, the investigators note.
Additional studies, the researchers say, are needed to delineate underlying mechanisms at play in the link between sodium intake and cognitive function.