Most packaged food labels don't list the amount of potassium the foods contain, according to a new study by New York City health workers.
That's concerning, researchers said, both because many health-conscious people want to make sure they're getting plenty of potassium, and some others - including those with impaired kidneys - have to restrict how much of it they consume.
Among people without potassium-related diet restrictions, the mineral has been tied to a lower risk of cardiovascular disease and death. The Institute of Medicine recommends most adults get 4.7 grams each day.
"Diets high in potassium help decrease the negative impact of sodium, and so having a high ratio of potassium versus sodium in your diet is really important," said Dr Susan Kansagra, who worked on the study at the New York City Department of Health and Mental Hygiene.
But, she added, "We know that Americans in general are consuming not enough potassium and are not meeting their dietary requirements."
How the study was done
Kansagra and her colleagues analysed the labels of 6 560 packaged foods from 61 different food categories using nutrition data from a salt-reduction program. Potassium contents were listed on just 500 of those products, the researchers report in JAMA Internal Medicine.
Potassium information was available for more than half of products in five of the 61 categories: vegetable juice, seasoned processed potatoes, instant hot cereal, French toast/pancakes/waffles and sauces.
The US Food and Drug Administration (FDA) currently requires sodium to be listed on nutrition facts, but potassium labelling is optional.
"The declaration of potassium is only mandatory when a nutrient/content or health claim about potassium is being made," a representative from the FDA said.
"The FDA is currently undergoing rule making to update the Nutrition Facts label."
Concern about lack of listing
Kansagra, New York's Assistant Commissioner of the Bureau of Chronic Disease Prevention and Tobacco Control, said the FDA should consider requiring companies to list potassium content on food labels.
"Given the importance of potassium in improving cardiovascular health, we think that would be an important addition," she said.
"It would allow consumers to make informed decisions."
People who are interested in upping their potassium intake should eat lots of fresh fruits and vegetables, according to Kansagra.
Meat, fish, soy and dairy are also good sources of the mineral. Nutrition researcher Dr Eric Matheson, from the Medical University of South Carolina in Charleston, said the lack of potassium labelling "is a very important public health concern," particularly for people who can't get too much of it.
"We have a lot of patients who have mild to moderate kidney failure, and having high potassium is very dangerous for them," said Matheson, who wasn't involved in the new study.
"I've had a number of patients be hospitalised and quite ill because their potassium got to be too high." For them, he said, avoiding food high in potassium often comes down to a guessing game.
Potassium may also alter the way some drugs work in the body. In another study published in the same journal issue, Canadian researchers found that patient education sheets about the anti-clotting drug warfarin were often lacking critical information.
The sheets contained, on average, less than two-thirds of the 50 items, such
as drug or food interactions and other warnings, that the researchers deemed
essential or important. The sheets were also written at reading levels five or
six grades higher than many people can understand.