Feeling down is a natural reaction to health struggles. But depression may also be an early warning sign of impending illness. One example: a new study from the journal Neurology finds people with depression may be at greater risk for Parkinson’s disease.Compared to people without clinical depression, those diagnosed with the mental illness are more than twice as likely to eventually develop Parkinson’s, the study shows. And the more severe your depression, the stronger the link to Parkinson’s becomes, the study data show.
It’s possible that major depression causes damage to the brain that contributes to Parkinson’s, says study coauthor Peter Nordström, PhD, a professor of geriatric and community medicine at Sweden’s Umeå University. Nordström says it’s also possible that the drugs used to treat depression contribute to the development of Parkinson’s—or that depression is just a very early symptom of the disease. “From the present study, we can’t tell the answer,” he adds.
Unfortunately, Parkinson’s is just one of a handful of diseases for which depression may be an early red flag. Here are five more:
Another Neurology study found an association between depression and dementia. In fact, the authors of that study say depression may be among the earliest warning signs of the brain disease. Unfortunately, like the Parkinson’s researchers, the study team says it’s not clear if depression is a cause of dementia, or simply an early symptom.
Several studies have tied depression to a greater risk for heart disease and heart attack. One Norwegian study found the risk of heart failure jumped 40% among those suffering from major depression. The study’s authors say depression can raise a person’s stress levels. Stress hormones promote inflammation and the buildup of arterial plaque—both of which could explain the mental illness’s links to heart trouble.
Since at least the 1930s, doctors have observed a link between depression and certain forms of cancer—particularly pancreatic cancer. A recent study from the Yale School of Medicine found that people who eventually developed pancreatic cancer were much more likely to have experienced depression prior to their diagnosis than other types of cancer sufferers. It’s possible pancreatic tumor cells release a protein that blocks some feel-good receptors in the brain, the study’s authors say.
One recent study from the Mount Sinai Medical Center in New York suggests that, for some people, depression may actually be an allergic reaction to stress. Among mice, stress hormones caused some rodents’ immune systems to overproduce a compound called Interleukin-6. That compound increased fatigue, distorted appetite, and lead to other symptoms often associated with depression. Interleukin-6 spikes among some people with depression, the Mount Sinai Medical Center study authors say. So it’s possible that your blue mood may actually be your immune system overreacting to stress as though it were an allergen. (Add these 13 stress-fighting foods to your diet.)
Your thyroid produces hormones and proteins that regulate many of your body’s systems. Your thyroid is also a bit of a mystery. Studies have linked an over- or under-active thyroid to everything from thinning hair to excessive weight gain and feeling cold all the time. Plenty of research has also linked thyroid problems to depression. A recent study from the Journal of Thyroid Research found people diagnosed with depression are more likely to have thyroid problems—and vice versa. If your low mood is accompanied by fatigue, weight gain, or other physical symptoms, issues with your thyroid may be partly to blame, the study suggests. MORE: 9 Highly Effective Treatments For Mild Depression