That’s according to new research from the University of Southern California, whose researchers have recently published two papers on the topic. 

In the first, published in Alzheimer’s Research & Therapy, researchers analyzed data from 40 million Medicare beneficiaries ages 65 and older and compared the number diagnosed with the condition to the number they would expect to be diagnosed. About 8 million Americans in that group likely have MCI, they predicted—about 13% of the country’s senior population or 1 in 7 seniors. But only 600,000 had received a proper medical diagnosis.

A second study, published Tuesday in The Journal of Prevention of Alzheimer’s Disease, also found that MCI is “vastly underdiagnosed,” with 99.9% of U.S. primary care clinicians not sufficiently catching cases. Only about 8% of U.S. residents with the condition have been diagnosed, researchers concluded after crunching the numbers on data from nearly 250,000 U.S. doctors.

Nearly 7.5 million older Americans are likely living with MCI unaware, researchers say. It’s a problem they’d like to solve for a couple of reasons: Contrary to popular belief, MCI isn’t a part of the normal aging process. And recently approved drugs may help preserve cognitive function in patients in the early stages of decline—but not in later stages.

While detection of the condition is generally poor in the U.S., it’s even worse among patients from historically disadvantaged groups—including Black and Hispanic Americans, and those with less education. Not only that, but the risk of developing the condition is also higher in such groups as well, researchers say.

And that’s a tragedy. Because in cases of MCI caused by Alzheimer’s disease, “the earlier you treat, the better the outcomes,” Dr. Soeren Mattke, director of the Center for Improving Chronic Illness Care at the University of Southern California and a co-author on both studies, tells Fortune. “This means even though the disease may be slowly progressing, every day counts.”

What to do if you’re concerned about MCI

Those who have memory concerns—who sense they’re becoming more forgetful, having difficulty keeping track of time, and/or getting lost more often—should bring the subject up to their primary care provider. Those who are a caregiver of someone experiencing such changes should schedule an appointment for their loved one and attend, Mattke says.

Primary care providers can perform a quick assessment and decide whether you or your loved one should be referred to a specialist, like a neurologist or geriatrician, who can perform more in-depth cognitive testing. 

It takes a bit of preparation for a primary care provider to perform a preliminary cognitive assessment. So if you’re seeking one, let your doctor’s office know when you schedule instead of springing it on them at the appointment, Mattke recommends.

If you’re middle-aged or younger, you likely don’t have MCI, which is “very aging-related,” he adds. The number of those in those in their 50s with MCI “is still pretty low.” It’s generally found among those 65 and older.

MCI’s connection to Alzheimer’s disease

MCI is a symptom set, and the cause isn’t always Alzheimer’s disease, Mattke said. Still, about half of cases of MCI are due to early Alzheimer’s. And now that there are U.S. Food and Drug Administration-approved treatments to slow disease progression, it’s more crucial than ever to see a doctor if you’re concerned.

Before this summer, when lecanemab (Leqembi) was approved by the FDA, doctors often wouldn’t perform the physical tests needed to diagnose early Alzheimer’s—like a PET scan or cerebral spinal fluid analysis—on patients with MCI because even if they had the disease, doctors couldn’t slow the progression.

Now that the drug has been approved, patients who were previously diagnosed with MCI should return to their doctors and ask if tests for Alzheimer’s should be run, with the goal of starting treatment, if appropriate, Mattke recommends.

Lecanemab is like “Drano for the brain” and involves an IV infusion performed at a medical center—perhaps as frequently as every two weeks, he said. While it can’t reverse the condition—lost brain cells don’t regenerate—it can clear amyloid plaques and tau tangles from the brain, slowing the progression of the disease.

While the treatment isn’t a cure, it may allow some Alzheimer’s patients to “live out their biological lifespan and still recognize their spouse when they go to bed in the evening.”

It’s incredibly important that patients facing a potential Alzheimer’s disease diagnosis realize that “we have a treatment,” Mattke said—but “time is not on your side.”