The cruel interplay between depression and Parkinson’s disease has become reality for Jackie Hunt Christensen, a national Parkinson’s advocate from Minneapolis.

While exercise can alleviate sadness and low moods, the worsening symptoms of Parkinson’s —an incurable neurological disorder that erodes mobility and thinking skills — are making it harder for her to stay active. Christensen had to skip a national Parkinson’s conference she has routinely attended. And a new symptom, retropulsion or an involuntary tendency to tip backward, has increased the risks for falls and limited even moving around home.

All of which makes it harder to combat depression.

“As the disease progresses,” she said, “you’re not able to do things that you used to do, and you’re grieving that.”

Recent research has clarified how common it is for depression and Parkinson’s to occur at the same time; one study found depressive symptoms in 70 percent of people with Parkinson’s. But the issue didn’t gain much public attention until the death of comedian Robin Williams — whose suicide this month came after his Parkinson’s diagnosis.

“Everybody with Parkinson’s is all of a sudden examining themselves,” said Dr. Steven Stein, a Minneapolis neurologist. “I have received many phone calls from patients who are sort of freaking out about, ‘Is this going to happen to me?’ ”

The connection to depression is far more complicated than patients growing despondent over a Parkinson’s diagnosis — though doctors said that frequently occurs. Parkinson’s impact on movement and thinking skills comes from the gradual loss of dopamine, a chemical necessary for communication among brain cells that also triggers feelings of happiness.

“Dopamine is sort of a feel-good neurotransmitter,” Stein said. “It’s involved with our sense of enjoyment, our sense of pleasure. It would be surprising that anything that could disrupt those pathways wouldn’t contribute to depression and anxiety as well.”

In some cases, depression comes years before symptoms of Parkinson’s. In others, people appear depressed but are just showing early signs of Parkinson’s before diagnosis.

A loss of facial expression is a common early characteristic of Parkinson’s, which creates the appearance of depression because people don’t appear to be as enthusiastic, said Dr. Martha Nance, a neurologist with the Struthers Parkinson’s Center in Golden Valley.

Christensen, 50, has struggled with depression since childhood, and has taken antidepressants before and after her Parkinson’s diagnosis at age 34. Deep brain stimulation in 2006 helped reduce motor symptoms such as tremors and rigidity. But the surgical procedure, which implants a device that delivers nerve impulses to the brain to counter the loss of dopamine, didn’t affect the disease’s impact on mood, fatigue and cognitive skills.

She turned to books, her cats, talks with friends and family members, and her advocacy work to stay positive and active — along with watercolor painting and glass art when feeling good. Her recent mobility decline has been frustrating, though, as Christensen has suffered several falls and has installed grab bars around her home for safety.

“When I start wallowing in self-pity a little bit too much, I get a copy of my book called ‘Tuesdays With Morrie,’ ” about an elderly man dying of ALS, she said. “That reminds me that I still feel very blessed.”

Daily exercise helps Liz Ogren overcome her depressive symptoms. So the Edina woman has been aggressive with her Parkinson’s medications since her diagnosis seven years ago — using higher doses that allow her to exercise and be an active mother to her two sons as they finish high school.

The trade-off is that aggressive use of the medication can result in more rapid development of a side effect known as dyskinesia, an involuntary movement of limbs that is often mistakenly associated as a symptom of the disease.

One day, the maximum dosage might not hold back the progression of the disease, said Ogren, 51. “Then I’m hoping to God they have come up with another solution.”

Ogren and Christensen grieved for Williams.

“I really wish he could have held on and reached out to the Parkinson’s community because I think he would have found a tremendous amount of support,” Christensen said. “And it’s ironic because laughter and a good sense of humor are so important to coping with Parkinson’s and he brought the world so much of that.”

How doctors approach patients at key junctures, such as when their symptoms worsen, is important in dealing with their depression, said Christensen, who is state volunteer director for the Minnesota Parkinson’s Action Network. She also wrote a book in 2004 for people newly diagnosed with Parkinson’s.

“I know people who, when they’ve been diagnosed, the doctor has said, ‘Well, there is some medication, but it only works for five years and then you’re done,’ ” she said. “If you get a message like that from the medical establishment, it’s not exactly a day brightener.”

Nance said there is no five-year window for Parkinson’s medications. Many of her patients have lived healthy, active lives — some for more than 30 years. While depression can complicate Parkinson’s, the flip side is that patients have discovered that exercise and treatment can address both disorders.

“Depression and Parkinson’s disease are treatable and, I think, sometimes on Day 1 of a diagnosis, people fall into despair,” she said. “If they just get through that, get the support they need, they can live on to find out there still is a tomorrow and that there can be a better tomorrow. The tragedy is Robin Williams didn’t live long enough to experience that.”