Carers should be routinely screened for signs of depression by their GP to ensure their health needs are not neglected, doctors' leaders say.
The Royal College of General Practitioners (RCGP) estimates one in every 20 patients registered with a GP practice is providing unpaid care.
About 40% of carers are thought to be at risk of depression or stress because of their caring role.
Charity Carers UK said GPs had a vital role to play in supporting carers.
It is estimated that seven million people in the UK currently provide unpaid care to a sick or disabled child or an adult who could not otherwise live independently.
Many of them are already known to GPs, but the RCGP says more should be done to improve the support and services offered to carers.
It says the "screening" process for depression should involve "a small number of general, non-invasive, questions about mood and mental wellbeing".
The RCGP has also drawn up a list for clinical commissioning groups - groups of GPs that plan local care - of measures to ensure carers' needs are taken into account:
- Improve GP access by allocating routine appointments and vaccinations at convenient times for carers
- Appoint a carers' "champion" in all GP surgeries
- Maintain a carers' register within the GP practice
- Carry out audits to measure improvements in carer support
Dr Clare Gerada, chairwoman of the Royal College of GPs, said carers often found it hard to admit they were struggling.
"Carers often neglect their own healthcare needs and in many cases it is only a matter of time before they themselves become ill.
"GPs can play a crucial role in identifying potential problems in the early stages and 'screening' for depression is something that many GPs are doing already.
"Commissioners need to invest in supporting carers as a critical asset.
"They already save the public purse £119bn a year and this initiative could save even more by ensuring that carers stay well enough to keep on caring."
Fear and anxiety
Eileen Skidmore, from Birmingham, has been caring for her mother for more than 20 years.
She also cares for a disabled friend.
My health has definitely suffered," she said.
"I am constantly depressed and agitated, yet I get little consideration from healthcare professionals.
"I run a group for carers and this definitely helps me.
"It's only once a month but it gives me and others a bit of respite."
Helena Herklots, chief executive of Carers UK, said caring full-time for a family member could leave people cut off from the outside world.
"This isolation, alongside the pressures, fears and anxieties of supporting an ill or disabled loved one, can take a serious toll on carers' mental health," she said.
"NHS and social-care services, particularly GPs, are often the first port of call for families with caring responsibilities - they have a vital role to play in identifying carers and helping them access the support they need."
The government's care bill will help people find what support is available to them, a Department of Health spokesperson said.
"We know far too many carers can suffer depression, emotional and physical exhaustion - and it is important that they do not bear this responsibility alone.
"GPs have a critical role to play in identifying people with a caring responsibility and assessing their needs for support, including with depression."