Tired brains, COVID rebound and sustainable food

Asian online businesswoman working at night.  Busy and exhausted from working overtime at home.

Mental stress can lead to changes in the brain’s physiology that cause a feeling of fatigue.Credit: Getty

Why thinking hard makes us feel tired

It’s not just in your head: a desire to curl up on the couch after a day of toil at the computer can be a physiological response to mentally taxing work, according to a study linking fatigue to changes in brain metabolism (A. Wiehler) et al. Curr. Biol. https://doi.org/gqm8kv; 2022).

The study found that participants who spent more than six hours working on a boring and mentally demanding task had higher levels of glutamate – an important signaling molecule in the brain – than those who had completed simpler tasks. Too much glutamate can disrupt brain function, and a period of rest can allow the brain to restore proper regulation of the molecule, the authors note.

The work is important in its effort to link cognitive fatigue with neurometabolism, but more research – potentially in non-human animals – will be needed to establish a causal link, says behavioral neuroscientist Carmen Sandi at the Swiss Federal Institute of Technology in Lausanne. “It’s really good to start looking into this aspect,” she says. “But for now, this is an observation, which is a correlation.”

Healthier foods are better for the planet, huge studies find

Healthier foods tend to be more environmentally friendly than foods with low nutritional value, an analysis of more than 57,000 foods sold in the UK and Ireland finds (M. Clark et al. Proc. Natl Acad. Sci. USA 119, e2120584119; 2022).

The mammoth study is among the first to estimate the environmental impact of products made with multiple ingredients, rather than looking at individual products. Researchers used an algorithm to estimate how much of each ingredient was in thousands of products sold in major supermarket chains. They then gave products an environmental impact score out of 100 – with 100 being the worst – by combining the effects of the ingredients in 100 grams of each product. They considered several factors, including greenhouse gas emissions and land use.

Food for thought: Scatterplots comparing the environmental and nutritional impact of a range of foods.

Source: M. Clark et al. Proc. Natl Acad. Sci. USA 119e2120584119 (2022).

Comparing environmental impact scores with nutritional information showed that healthier foods tended to have a low environmental impact. There were some notable exceptions: both nuts and seafood have a good nutrition score but relatively high environmental impact, for example.

The information can help consumers understand how goods compare in terms of both nutrition and sustainability, say the researchers.

Health workers perform a Covid-19 swab test on a resident in the Xuhui District of Shanghai, China

A healthcare worker swabs a person in Shanghai, China, for SARS-CoV-2.Credit: Qilai Shen/Bloomberg via Getty

COVID rebound is common without antiviral therapy

In some people taking the antiviral drug Paxlovid for COVID-19, symptoms and detectable virus levels reappear days after they disappeared. Now studies suggest that it is common for SARS-CoV-2 to return in untreated cases, and suggest that the virus makes a harder comeback in people taking Paxlovid.

Jonathan Li, a physician-scientist at Brigham and Women’s Hospital in Boston, Massachusetts, and his team analyzed data from hundreds of people who received a placebo in a trial of COVID-19 drugs (R. Deo et al. Preprint at medRxiv https://doi.org/gqk4rm; 2022). More than a quarter of participants infected with SARS-CoV-2 reported that their symptoms regressed; 1 in 8 saw the virus return to high levels.

In a second study (M. Charness et al. Preprint at Research Square https://doi.org/h8n5; 2022), infectious disease physician and vaccine researcher Kathryn Stephenson at Beth Israel Deaconess Medical Center in Boston and her team followed 11 people who took Paxlovid for COVID-19 and 25 who did not. More than a quarter of the Paxlovid recipients rebounded, in terms of SARS-CoV-2 levels, compared to just one of the untreated people. Also, people with Paxlovid rebound had high levels of virus for several days. None of the studies have been peer-reviewed.

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