If you or a family member seem to be having memory problems, make sure low sodium levels aren't the reason. In some older adults declines in memory may be simply the result of blood sodium levels that are just a little too low.

Nearly 5,500 generally healthy men over the age of 65 with no symptoms of cognitive impairment were followed for about 4.5 years. One hundred of the men turned out to have hyponatremia, the clinical term for blood sodium levels below 135 mmol/L.

Certain medications that increase urination or perspiration can cause a loss of sodium. Drinking either too much or too little water can do it, too.

Hyponatremia used to be considered harmless, but it is now known to be linked to a higher possibility of falls, attention problems, cardiovascular events, irregular walking and even premature death. When severe, low sodium levels can cause neurological problems and mental impairment.

Men in the study who had sodium levels in the range of 126-140 mmol/L were 30 percent more likely to experience mental impairment at the beginning of the study and 37 percent more likely to show signs of mental decline over time, compared to men whose sodium levels were 141-142 mmol/L when the study began. Normal sodium levels are generally 135 to 145 mmol/L, though a particular laboratory may use different values as their “normal” range.

There are a number of reasons why sodium levels may become low. Certain medications that increase urination or perspiration can cause a loss of sodium. Drinking either too much or too little water can also lead to low sodium levels. Many heart, kidney and liver conditions, as well as chronic diarrhea or vomiting, can also cause the body to lose sodium.

“Slightly lower sodium levels in the blood are likely to be unnoticed in clinical practice,” said one of the researchers, Kristen Nowak, from the University of Colorado, in a statement. “Because both slightly lower serum sodium levels and mild changes in cognitive function are common occurrences with advancing age, future research on this topic is important — including determining whether correcting lower sodium levels affects cognitive function.”

The study is published in the Clinical Journal of the American Society of Nephrology.