That makes 8 pounds I’ve lost over the past four months,” my patient—an obviously concerned 80-year-old—reported, asking, “When is this going to stop?” She added that she felt well and that her appetite and activity pattern had not changed at all, even though she was losing weight without intending to.

Hers was not an uncommon complaint. As many as one in five adults older than 65 have significant undesired weight loss over time. And her concern was warranted because most physicians agree that an unexpected weight loss of 5 percent or more—and she’d lost about 6 or 7 percent—in such a short time is worrisome. Worrisome because unintentional weight loss, or UWL, is linked to a higher risk of sickness and even death. Thus, my first goal was to find the cause of the weight loss, which can be difficult.

Could Losing Weight Be a Sign of Cancer?

Uppermost in the mind of anyone with UWL is the possibility of cancer. Studies have shown that in up to 35 percent of people with substantial unintended weight loss, cancer was the cause. (The ways in which cancer can lead to weight loss are numerous, including, but not limited to, a reduced appetite.)

The good news is that if no cancer is detected on the initial evaluation, which should include a complete history, a physical exam, and some carefully selected tests, it’s unlikely that cancer is responsible. The importance of that evaluation cannot be underestimated, because when cancer is the cause of weight loss, at least one physical finding or lab test abnormality is bound to be found.

Common Causes of Losing Weight

After cancer, other common causes of UWL are gastrointestinal disease and mental health problems. Noncancerous diseases of the gastrointestinal tract account for 10 to 20 percent of UWL cases, even when appetite and bowel function remain normal. Sometimes signs and symptoms of conditions such as celiac disease and ulcerative colitis can be so subtle early on as to make detection difficult—with weight loss being the only apparent symptom.

In older adults and those in nursing homes, depression can have a powerful impact on eating behavior without being obvious to the victims. Mental health disorders, and particularly depression, account for up to 58 percent of cases of UWL in nursing home residents.

Many times, factors such as dementia, loneliness, poorly fitted dentures (or none), hearing loss, and medication effects may be the cause. Occasionally it’s situational. One elderly patient’s weight loss occurred as a result of skipping meals, and doing so simply because the walk from her room in the assisted living facility she lived in to the dining area was too far—and she was reluctant to admit it. When one or more of the above problems are corrected or improved, UWL will usually stop.

Those with hyperthyroidism and diabetes can also present with UWL and little in the way of other symptoms. In older adults, an overactive thyroid often masquerades as apathetic hyperthyroidism because typical signs, such as heat intolerance, frequent bowel movements, and nervousness, are lacking. Weight loss occurs despite a good appetite. Weight loss due to the loss of sugar (and therefore calories) in the urine may be the only manifestation of type 2 diabetes—elevated blood sugar might produce no symptoms.

The Diagnosis and Treatment

Despite our sophisticated diagnostic techniques, research shows that up to one in four people with significant UWL fail to get an adequate diagnosis. I thought that would hold true for my patient.

Imagine my surprise (and delight) when I detected an irregular heartbeat, of which she was totally unaware, in an otherwise normal physical exam. An electrocardiogram showed atrial fibrillation, an abnormal heart rhythm that’s sometimes associated with thyroid overactivity.

Her laboratory tests results, available the next day, confirmed my suspicion that she had an overactive thyroid. After a few weeks on medication to treat her apathetic hyperthyroidism, she gained not only the pounds she had lost but also a few more that she didn’t want. I smiled when she then regaled me with the same question she asked on that first visit: “When is this going to stop?”