The human brain's ability to juggle between two tasks begins to decline almost a decade earlier than expected, a new study finds.

Walking is usually done along with other activities like reading a signboard or talking to a friend. However, a recent study by Harvard Medical School and Hebrew SeniorLife found the ability to dual-task starts to decline by the age of 55, a decade before old age.

The study evaluated 996 adults between May 2018 and July 2020 to understand the relationship between age, dual-task gait and cognitive function in middle age (between 40 and 64 years).

"We assessed a large number of individuals between the ages of 40 and 64 years and observed that the ability to walk under normal, quiet conditions remained relatively stable across this age range," lead researcher Junhong Zhou said in the study published in Lancet Health Longevity.

"However, even in this relatively healthy cohort, when we asked participants to walk and perform a mental arithmetic task at the same time, we were able to observe subtle yet important changes in gait starting in the middle of the sixth decade of life," Zhou added.

The researchers found the diminishing ability to dual-task was due to changes in the underlying brain function and not changes in physical function. People with the declined ability are at a greater risk of falls and injuries, the study warns.

The decline in the brain's ability to perform two tasks at a time shows a decline in age-related brain function, which may indicate an increased risk of developing dementia later in life.

"As compared to walking quietly, walking under dual-task conditions adds stress to the motor control system because the two tasks must compete for shared resources in the brain," Zhou said. "Our study is important because it has discovered that changes in this type of brain resilience occur much earlier than previously believed...We hope our study will spur future research to discover lifestyle and other modifiable factors that support the maintenance of dual-task performance into old age, as well as interventions that target these factors."

Researchers also observed that although dual-tasking ability tends to diminish with advancing age, not everyone in the study fits this description.