A new study has warned that older frail husbands and wives pass on their depression and frailty to their spouses.
In what seems like a vicious circle, as one spouse becomes increasingly frail the more likely they will fall into depression. And as depression bites the person is more likely to become even more frail.
This then affects their other half so they too become down and frail.
Older husbands tended to be more depressed and frail than younger husbands while older wives were not more depressed, but were frailer than younger wives.
Frailty was defined as anyone having three or more conditions of either low body weight, weakness, exhaustion, slowness or physical inactivity and affects a tenth of the elderly.
While previous research has looked at the issue of frailty and depression in individuals, the study by Yale School of Public Health was the first to look at its affect on couples.
The aim was to establish whether older adult spouses' frailty states and depressive symptoms are interrelated over time.
Assistant Professor of Epidemiology Dr Joan Monin explained why this could happen.
She said: "First, spouses of frail individuals frequently act as caregivers, and caregiving can lead to depression.
"Second, frail spouses are often depressed, which can be contagious.
"Depressive symptoms may lead to greater frailty through different mechanisms.
" Depression can reduce the couple's social activity.
"Also, depressed spouses may lack the energy to provide support to their partners, exacerbating the partner's health problems."
These findings are based on a study of data from 1,260 married couples aged over 65 collected during the Cardiovascular Health Study.
This is a population-based longitudinal study designed to determine risk factors for cardiovascular disease in adults aged 65 and older
Prof Monin said: "Within individuals, greater frailty predicted greater subsequent depressive symptoms, and greater depressive symptoms predicted greater subsequent frailty.
"Between spouses, an individual's greater frailty predicted the spouse's greater frailty, and an individual's greater depressive symptoms predicted the spouse's greater depressive symptoms."
She added this supported the "contagion theory" that depression can be catching.
She said: "Thus, it seems that frailty is associated with depressive symptoms within an individual and that the resulting depressive symptoms have influences on spouses.
"It was also found that effects did not differ for husbands and wives. This contrasts with previous work on physical activity and the theory that women have more-interdependent identities than men."
She added: "Frailty and depressive symptoms are interrelated in older adult spouses.
"For older couples, interventions to prevent or treat frailty and depression that focus on couples may be more effective than those that focus on individuals."
She recommended doctors and those caring for the elderly should encourage couples to be active, socialise and provide support to break the cycle.
The study was published in the Journal of the American Geriatrics Society.