Cycling for just 17 minutes a day could boost your brain -- and maybe even ward off dementia, a study suggests.
Scientists in the UK tracked 23 overweight adults in their mid-30s and asked half to complete a 12-week cycling program, while the rest did little to no exercise.
After exercising, blood tests showed that those who cycled had a significant surge in brain-derived neurotrophic factor (BDNF), a chemical often dubbed the brain's 'fertilizer' because it helps neurons grow and communicate.
In people who did little to no exercise, levels of the chemical did not change.
Scans showed that cyclists' brains had lower activity during attention and inhibition tasks, which the researchers said suggested the organ was working more efficiently, and thus had improved function.
The study did not detect improvements in memory over the 12-week period, although researchers said that may have been because the trial was too short to capture these changes.
The team, led by Dr Flaminia Ronca, an exercise physiologist, wrote: 'These results suggest that increasing physical fitness can enhance BDNF [levels] in response to acute bouts of exercise.
'This might, in turn, play a part in the [improvement] of neural function during executive tasks after acute exercise.'
More than 7 million adults currently have dementia in the US, according to estimates, but that number is expected to nearly double by 2050.
In the study, published in the journal Brain Research, participants were recruited through university and community advertisements.
The group had an average age of 35, seven were women, and all said they exercised fewer than three times per week.
Those assigned to the exercise group were asked to complete four cycling sessions a week for 12 weeks, with workouts lasting between 30 and 45 minutes.
This equates to between 17 and 26 minutes per day.
For the first six weeks, participants mainly completed 'light' cycling, before increasing the intensity in the second half of the program.
Researchers measured effort using ratings of perceived exertion (RPE), a scale where participants rate how hard they feel they are working from one to ten, with one meaning very little effort and ten representing maximum effort.
During the first phase, volunteers completed one low-intensity ride each week, two moderate sessions and one high-intensity workout.
In the second phase, they completed two high-intensity rides, one moderate session and one lighter session each week.
Blood tests for BDNF were completed at the start, week six, and at the end of the study. Participants also had body composition scans and fitness tests.
Overall, those who cycled saw their body fat percentage fall from 23.4 to 22.4 percent.
Their fitness, measured as VO2 max -- which tests how efficiently the body uses oxygen -- also rose from 28.8 to 32.2 milliliters of oxygen per minute per kilogram (ml/min/kg).
For comparison, the group that did no exercise saw their body fat percentage remain at 25 percent while their fitness level fell from 29.8 to 27.7 ml/min/kg.
Tests showed cyclists had a clear surge in BDNF levels after exercise although BDNF levels remained the same in both groups while individuals were at rest.
Brain scans also picked up the reduced activity in the exercise group in the organ's prefrontal cortex, the front area of the brain that manages executive functions such as planning, focus and memory.
Dr Ronca told Daily Mail: 'Lower activity in the prefrontal cortex might potentially suggest more efficient functioning in those participants who produced more BDNF.'
More efficient functioning may suggest that someone might be able to maintain focus for longer.
Researchers said their results showed exercising boosted the body's ability to release BDNF.
A 2011 study, cited by the researchers to Daily Mail, linked increased production of BDNF to improved brain function and more volume in the hippocampus, the structure crucial for converting short-term memory into long-term, navigating spatial environments and learning.
The study did not show that exercise prevents dementia, though previous research has suggested a link between increased exercise and a reduced risk of the condition.
Physical activity is thought to reduce dementia risk because exercise boosts blood flow to the brain, helping to keep tissue oxygenated and remove waste particles, and reducing inflammation, which has also been linked to the disease.
The scientists noted that this study only found a correlation and could not definitively prove that the exercise was causing the change.
They also said that it was a small study, adding that larger studies would be needed to confirm the trend.