People who never or rarely saw their loved ones were 39 per cent more likely to die during a 13-year study, even if they lived with someone.
A monthly visit appeared to be the “threshold” to reduce risk and more frequent visits did not lead to further benefits, experts said.
Study co-author Jason Gill, professor of cardiometabolic health at the University of Glasgow, said: “The risk seems to be (among) people who are very isolated, and never ever see friends and family or see them less frequently than once a month.
“Ensuring that you visit your lonely and isolated relatives is a super helpful thing to do because it seems to be important that people have a visit at least once a month.”
The study, published in the journal BMC Medicine, analysed data from more than 450,000 people with an average age of 57.
It considered five examples of loneliness and isolation, including feeling like you have no one to confide in, not attending any weekly social groups, and living alone.
Experts said people would benefit most from having a range of different types of social interaction.
Dr Hamish Foster, a clinical research fellow in general practice and primary care at the University of Glasgow, said the study could not explain why social interaction benefits health.
But he suggested friends and family might help people access support, or “it could be that people who are more socially isolated may have some more unhealthy behaviours like smoking or high alcohol intake, for example”.
Caroline Abrahams, charity director at Age UK, said: “This is very interesting new research which confirms just how useful it is for us as we age to have close friends and family members who visit and care about us.
“The emerging health or other problems an older person has are more likely to be spotted in this situation, and positive and timely action taken.
“It’s really easy for all of us, at any age, to ignore a health concern and put off doing something about it, but having someone close we can confide can make a real difference.”
Ms Abrahams added that the more close relationships people have, the more likely a loved one will urge them to seek help if needed.
She added: “For some older people the offer of going along with them to an appointment or at least helping with transport may make the difference between them actively pursuing a health concern or continuing to brush it off, until they become seriously unwell.
“We all need that kind of support sometimes, especially now with the NHS under such pressure that some persistence from patients is often required, but sadly if you are isolated and alone then it won’t be available to you.”