Offering couples more reasons to celebrate love on this Valentine's Day -- and beyond, a new study has found that married people face less psychological stress than unmarried individuals.

Married individuals had lower levels of the stress hormone cortisol than those who never married or were previously married, showed the study published in the journal Psychoneuroendocrinology.

Prolonged stress is associated with increased levels of cortisol which can interfere with the body's ability to regulate inflammation, which in turn promotes the development and progression of many diseases.

"It is exciting to discover a physiological pathway that may explain how relationships influence health and disease," said one of the researchers Brian Chin from Carnegie Mellon University in Pittsburgh, Pennsylvania, US.

Over three non-consecutive days, the researchers collected saliva samples from 572 healthy adults aged 21-55. Multiple samples were taken during each 24-hour period and tested for cortisol.
 

The results showed that the married participants had lower cortisol levels than the never-married or previously-married people across the three day period.

The researchers also compared each person's daily cortisol rhythm -- typically, cortisol levels peak when a person wakes up and decline during the day.

Those who were married showed a faster decline, a pattern that has been associated with less heart disease, and longer survival among cancer patients.

"These data provide important insight into the way in which our intimate social relationships can get under the skin to influence our health," co-author Sheldon Cohen, Professor at Carnegie Mellon University, noted.