It's already proven that being lonely can be bad for your psychological health. But it can also affect your physical health, accelerating the body's aging process. That's according to a new study that found loneliness increases people's biological age more than regular smoking.

The study used an "aging clock" to test blood and biometric data from almost 12,000 Chinese adults. The researchers behind the study, led by biotech company Deep Longevity, said they were surprised to see how much of an impact psychological factors can have on aging, compared to physical factors such as smoking.

An aging clock is a statistical model that measures biological age, rather than chronological age – showing how old a person actually is based on their date of birth.

The researchers said the most important predictors of age were blood pressure, cystatin C (a protein that signals kidney health), body mass index (BMI) and spirometry (lung capacity).

After analyzing data from 11,914 Chinese adults, the clock determined that smoking added about 1.25 years to aging.

However, feeling lonely can add 1.65 years to aging.

However, loneliness was not the only feeling that contributed to accelerated aging, but a whole psychological cluster designed to measure well-being that also included fear, hopelessness, depression, dissatisfaction and poor sleep.

Those who had never married were also found to have an extra 0.35 years of age due to their single status, while people living in rural areas had an extra 0.39 years of age.

Mental health, the main driver of aging

Manuel Faria, another author of the paper, argued that "mental and psychosocial conditions are some of the most powerful predictors of health outcomes - and quality of life - but they have been largely left out of modern health care."

He said that the psychological aspect of aging should not be neglected in either research or practical anti-aging applications.

The authors concluded that given the strong link between psychological states and aging, poor mental health should be recognized as a major driver of aging.

The study was published in the journal Aging-US .