Scientists around the world are trying to use artificial intelligence to create a new type of 'clock' that can measure your true biological age.
A recent attempt added psychological factors to the mix and made some intriguing predictions. The initial tests suggest that the impact of mental ill health could, at times, outweigh those of physical diseases and habits, including smoking.
Chronological age is based on how many years are tucked under your belt, but just because two people have celebrated the same number of birthdays doesn't mean they are equally healthy.
By measuring certain aspects of a person's physical health, like the gut's microbiome or inflammation markers in the blood, researchers hope to one day predict how 'young' or 'old' someone is in biological years.
If the forecast is accurate, it could help experts understand why some individuals age faster than others and what lifestyle factors contribute to that aging process.
But there's a key component of human health that's been missing from previous clock-winding attempts: our mental and emotional state.
In 2021, a decades-long study among 2.3 million New Zealanders found a strong association between mental disorders and the onset of physical disease and death.
Another study that same year found that a history of mental health issues was associated with accelerated aging in midlife. What's more, this aging effect occurred many years before other age-related diseases tend to pop up.
With these findings in mind, researchers in the United States and Hong Kong designed a computer algorithm to create a new aging clock that incorporates several psychological health factors and blood biomarkers.
They trained the algorithm on data from nearly 5,000 healthy adults in the China Health and Retirement Longitudinal Study (CHARLS) dataset, which only includes participants 45 or older, and then tested it on data from another 7,000 people.
This is the first time researchers have trained an aging clock exclusively on such a large Chinese cohort (most studies are done in Western populations), and it's also among the first to incorporate mental health stressors.
Ultimately, the authors found psychological factors, such as feeling unhappy or lonely, added up to 1.65 years to a person's biological age. The effect exceeded other individual demographic characteristics, including biological sex, living area, marital status, and smoking status.
"We conclude that the psychological component should not be ignored in aging studies due to its significant impact on biological age," the authors write.
Deep Longevity, a publicly-traded company investing in deep aging clocks, funded the study.
This latest attempt incorporates physical information on 16 blood factors – including cholesterol levels – as well as BMI, waist circumference, and blood pressure.
The participants' psychological well-being data were based on eight feelings: bothered, lonely, unhappy, unfocused, restless, depressed, hopeless, or fearful.
This is a simplified version of mental health, but if anything, that would make the predictions of the biological clock more conservative.
When the clock was tested specifically on sick individuals, including those living with cancer, heart disease, liver disease, lung disease, or stroke, it accurately predicted that they were older than their counterparts in the main, healthy cohort.
But the effect of these conditions on predicted age did not exceed 1.5 years. That's slightly less than the aggregate impact of all the psychological variables put together, which accelerated aging by 1.65 years, according to the algorithm.
Smoking, meanwhile, added about 1.25 years of aging on its own.
This doesn't mean that the algorithm found smoking less of a risk to health than depression or loneliness; smoking remains one of the leading risk factors for many cancers and heart disease.
But based on the clock's predictions, it may be that if an unmarried person (which adds 0.59 years of aging) rarely feels happy (adds 0.35 years), often feels hopeless (adds 0.28 years), and is having trouble sleeping (adds 0.44 years), that might have a bigger impact on their health than smoking on its own.
The authors say their results demonstrate that the "detrimental impact of low psychological well-being is of the same magnitude as serious diseases and smoking".
"Thus," they conclude, "promoting mental health may be considered a potential anti-aging intervention with possible benefits [on] par with more tangible, physical therapeutic approaches."
The study was published in the journal Aging.