Family caregivers are invisible.

Those children, spouses, or other relatives who provide personal assistance to loved ones with physical or cognitive limitations are often taken for granted or even ignored. But without them, our system of long-term supports and services would collapse. Frail elders and younger people with disabilities would get sicker. Hospitalizations would increase. Medicare and Medicaid costs would explode.

There are at least 40 million family members caring for adults in the US. According to a new study by the AARP Public Policy Institute, they provided 37 billion hours of assistance in 2013, or an average of 18 hours a week. And AARP figures the economic value of that care was $470 billion. To put it another way: that’s roughly what it would cost to replace that family assistance with paid services.

Yet, we have a care system with only a vague sense that those families are there. It does little to understand their needs or what could be done to make their role easier and more effective.

Earlier this month, AARP updated its snapshot of caregivers, called Valuing the Invaluable. It builds in part on a study released in June called Caregiving in the U.S. that was done jointly by the National Alliance for Caregiving and AARP. Together, the two reports paint an important picture of those caregivers, and their enormous physical, financial, and emotional burdens.

Adult children, mostly daughters, reduce their own paid work to care for parents, at a lifetime cost that can reach hundreds of thousands of dollars. They struggle to provide complex medical care with little or no training. And, yet, the physicians treating their loved ones rarely talk to them.

The Caregiving study found that only one in three family caregivers reported that a doctor, nurse, or social worker asked their advice about caring for their loved one. Just one in six caregivers said a health provider ever asked if they needed help themselves.

At a time when hospitals are focused on preventing readmissions (thanks to Medicare penalties for those that have too many), health professionals who fail to ask these questions are ignoring key allies in their efforts to assure patients comply with, for example, post-hospitalization discharge instructions.

For instance, imagine how useful it would be for a physician to know whether an 80-year-old woman recovering from hip surgery will have transportation to her physical therapist once she returns home. Or has someone to help her take her pain pills on schedule. Or help cook her meals so she does not become malnourished.

None of this is high-tech medicine. But for the well-being of that surgery patient it can make all the difference between a good outcome and a poor one.

Similarly, if an over-burdened family caregiver crashes from the stress, the patient is highly likely to end up in a hospital or nursing home. A decline in a caregiver’s health often sends her loved one from home to a facility.

So when an adult daughter accompanies her mom to the doc, that physician could take a minute to ask the daughter how she is doing. True, she is not his patient. But knowing more about her physical and psychological state could be critical information.

Person-and family-centered care is all the rage in medicine these days. But while health professionals have learned to say the words, few really know what they mean.

As the AARP study notes, we are beginning to acknowledge the role and needs of caregivers. Thirteen states have enacted the Caregiver Advise, Record, Enable (CARE) Act that requires hospitals to take three steps for all patients: If a patient agrees, designate a caregiver at admission; notify her before the patient is discharged; and describe the tasks she will need to perform at home and provide instruction in how to do it.

In addition, 15 states now include a formal assessment of family caregivers for Medicaid recipients getting long-term supports and services at home.

These are important, though modest, steps. Slowly, policymakers are beginning to understand that in many cases, it is literally not possible for people with long-term care needs to live at home without the support of family caregivers. And they are starting to realize that hospital discharges will often fail without that family help.

We have a long way to go, but it is at least a start.