Despite a number of studies questioning the usefulness of very low-salt diets in the past few years, most major medical organizations continue to recommend them. We would assume that they do so from a strong base of evidence.

But with respect to heart failure, there is a shockingly small amount of evidence. Heart failure occurs when the heart cannot pump enough blood to the rest of the body. About 5.7 million people in the United States suffer from it.

Researchers reported in JAMA Internal Medicine that they searched for randomized controlled trials that evaluated reduced sodium to treat heart failure. They found nine studies that involved 479 patients. None involved more than 100 patients. There were no data that showed that salt restriction reduced mortality or cardiac disease or affected whether someone was hospitalized. In an accompanying editorial, Clyde Yancy, a professor of cardiology at Northwestern School of Medicine, wrote that the evidence for sodium restriction is “vacuous, lacks depth, and in some cases lacks integrity.”

Data on kids’ risk of secondhand smoke

Infants and toddlers in low-income communities may be even more at risk from second- and third-hand smoke exposure than has been believed, said new federally supported research. In testing that included more than 1,200 children, researchers found that as many as 15 percent of them had levels of cotinine, a byproduct of the body’s breakdown of nicotine, comparable with what would be found in an adult smoker. Overall, about 63 percent had discernible levels of cotinine, said the study in the journal Nicotine & Tobacco Research.

Lisa M. Gatzke-Kopp, a professor at Pennsylvania State University, said researchers plan to use the data to learn whether such increased exposure is related to later health problems, including learning deficits.

Hospital-acquired infections declining

The risk of getting a hospital-acquired infection is decreasing. In a study published in the New England Journal of Medicine, researchers surveyed almost 200 hospitals caring for about 12,000 patients across the country in 2011 and again in 2015, reviewing medical records to find cases of health care-associated infection. They found that in 2015, hospital-acquired infections had declined to 3.2 percent of patients, from 4 percent in 2011. They calculate that a patient’s risk of getting infected during a hospital stay was 16 percent lower in 2015 than in 2011.

Fentanyl ranked deadliest U.S. drug

Fentanyl now ranks as the deadliest drug in the U.S., health officials said. The synthetic opioid that’s up to 50 times more powerful than heroin was responsible for 18,335 overdose deaths in 2016, more than any other drug, the National Center for Health Statistics said. The report found 29 percent of all overdose deaths in 2016 involved fentanyl. By comparison, heroin caused 15,961 overdose deaths in 2016, the most recent year included.

Learn to be scientist with a virtual lab

How much do you know about anatomy? Cardiology? Have you ever set foot in a scientific lab? Once you visit BioInteractive’s virtual lab, you’ll feel as if you have. The website, hhmi.org, is offered by the Howard Hughes Medical Institute. It features free virtual labs for anatomy, bacterial identification, immunology, neurophysiology and cardiology. You tool around virtual, web-based spaces as if you were a scientist and learn as you go. It’s designed to help users practice the skills and techniques of scientific research.