Knowing how key cognitive functions could change in people diagnosed with Alzheimer's disease can make a significant difference to patients and those caring for them.

Although the underlying pathology is similar in most with the condition, the rates and severity of their deterioration varies.

A prospective study conducted by an international team of researchers has now confirmed age, sex, irregular heart rhythms, and daily activity levels provide the most reliable predictors of declining cognition.

"Even in the early stages of Alzheimer's disease, cognitive deterioration was best predicted by a combination of patients' demographic, somatic, and functional variables," write the researchers in their published paper.

The researchers started with a group of 500 Alzheimer's patients, following them over the course of two years. The drop-out rate was relatively high however, with only 169 patients still involved with the study by the end of that two-year period.

Data was logged for numerous demographic, health, and functional factors including experience of pain, depression, and neuropsychiatric symptoms.

Measures of cognitive decline were significant for all of the participants, though there was sufficient variation to uncover some relationships. Being older, being female, having difficulty with daily activities, and having a history of atrial fibrillation (issues with irregular heart rhythms) were identified by the researchers as predicting the biggest declines in cognitive ability.

These four predictors, logged at the start of the study period, accounted for around 14 percent of the variance in patient cognitive functioning in the final quarter of the two-year study period.

And it's not just the patients who are affected. Unsurprisingly, the burden on caregivers rose as cognitive abilities declined, suggesting those who support patients in their daily lives need to be considered in weighing up treatment options and disease progression, the researchers say.

While some variables weren't accounted for, including smoking and drinking habits, the findings are robust enough to suggest that demographics, medical history, and measures of daily activity could be enough to predict the rate of cognitive decline brought on by Alzheimer's.

As research continues, we're getting better at predicting how Alzheimer's might progress: a recently developed technique uses brain scans and various biomarkers to predict cognitive decline over five years, for instance.

Alzheimer's is the most common form of dementia, affecting tens of millions of people worldwide, and as that number continues to rise with an aging population, research like this can better tailor treatments and support.

"These findings underscore the importance of a comprehensive treatment approach, considering both patient and caregiver variables, in the diagnosis and treatment of early-stage Alzheimer's disease," write the researchers.

The research has been published in PLOS ONE.