New York,  Exercise and a healthy diet in childhood leads to adults with bigger brains and lower levels of anxiety, a new study suggests.

The mouse-model study determined that early-life exercise generally reduced anxious behaviors in adults. It also led to an increase in adult muscle and brain mass.

"During the Covid-19 lockdowns, particularly in the early months, kids got very little exercise. For many without access to a park or a backyard, school was their only source of physical activity," said researcher Marcell Cadney from the University of California - Riverside.

"It is important we find solutions for these kids, possibly including extra attention as they grow into adults," Cadney added.

The researchers determined that early-life exercise generally reduced anxious behaviours in adults. It also led to an increase in adult muscle and brain mass. When fed "Western" style diets high in fat and sugar, the mice not only became fatter, but also grew into adults that preferred unhealthy foods.

For the study, published in the journal Physiology and Behavior, the researchers divided the young mice into four groups -- those with access to exercise, those without access, those fed a standard, healthy diet and those who ate a Western diet.

Mice started on their diets immediately after weaning and continued on them for three weeks, until they reached sexual maturity.

After an additional eight weeks of "washout," during which all mice were housed without wheels and on the healthy diet, the researchers did behavioural analysis, measured aerobic capacity, and levels of several different hormones.

One of those they measured, leptin, is produced by fat cells. It helps control body weight by increasing energy expenditure and signaling that less food is required.

Early-life exercise increased adult leptin levels as well as fat mass in adult mice, regardless of the diet they ate.