People who are most active in the afternoon could be at increased risk of dementia, study finds

Being more productive in the afternoon could increase your risk of dementia, worrying new research suggests.

Scientists in the US found that older adults who were most productive after 2pm were more likely to develop the memory-robbing disease than those who peaked earlier. 

Experts say this could be due to afternoon bursts of energy disrupting the body’s natural functioning, preventing it from clearing toxic proteins that build in the brain. 

The study is the latest in a growing body of research linking interruptions to circadian rhythm – the body’s natural 24-hour internal clock – with a higher risk of the disease.

Nearly one million people in the UK currently have dementia – and it’s the country’s biggest killer, claiming more than 75,000 lives a year.

The condition can be caused by a number of factors, including genetics, brain changes, poor diet, smoking and lack of physical activity. 

But increasing evidence suggests that dementia could also be linked to changes in the body’s internal clock, which governs sleep and wake cycles as well as regulating biological processes like hormones, temperature and appetite. 

A new study from researchers at the University of Texas Southwestern tracked the cognitive health of more than 2000 older adults over three years. 

Participants, who had an average age of 79 and did not have dementia, first had their circadian rhythms measured over 12 days by wearing small heart monitors.

They were then divided into those with a ‘strong’ circadian rhythm – or a more extreme difference between their most and least active periods – and those with a less extreme, or ‘weak’ rhythm. 

Their most active period of the day was also measured. 

After three years, researchers discovered that participants who reached peak activity levels at 2.15pm or later were 45 per cent more likely to develop dementia than those who peaked earlier. 

Those with a weaker circadian rhythm were also more 2.5 times more likely to develop the disease than participants with a strong rhythm.

Publishing their findings in medical journal Neurology, the research team suggested that later bursts of energy could signal a mismatch between the body’s internal clock and environmental cues such light and dark cycles. 

When this occurs, the body fails to feel tired as the day ends, causing a late burst of energy. 

Over time, research has shown, this can lead to poor sleep, hormonal chaos, and systemic inflammation. 

Previous research has linked weaker and fragmented circadian rhythms to higher dementia risk. 

The study’s lead author, assistant professor at UT Southwestern Medical Center Dr Wendy Wang said that disruptions in circadian rhythm ‘may alter body processes like inflammation, and may interfere with sleep’.

A combination of these factors could contribute to development of the disease by ‘increasing amyloid plaques linked to dementia or reducing amyloid clearance from the brain,’ she added.

Amyloid plaques are sticky clumps of proteins that build up in the brain, disrupting nerve cells, which can lead to the illness.

The professor also called for further studies to look at potential interventions such as ‘light therapy or lifestyle changes’ to see if they can lower people’s risk of dementia.

The findings come as dementia cases continue to rise in the UK, with nearly one million Britons currently affected – a figure projected to reach 1.4 million by 2040.

While the condition has no cure, early diagnosis can help slow progression and manage symptoms, which include memory loss, difficulty concentrating, mood changes and problems following conversations.

Growing evidence suggests changes in vision, hearing, taste, touch and balance can appear years before classic symptoms.

Experts have also warned that problems with spatial awareness, such as standing too close to others, may emerge up to 20 years earlier.

According to the Alzheimer’s Society, dementia costs the UK £42 billion a year, with families shouldering much of the burden. That figure is expected to rise to £90 billion within 15 years.

Separate analysis by Alzheimer’s Research UK found 74,261 people died from dementia in 2022, up from 69,178 the previous year – making it the country’s single biggest killer.