WEDNESDAY, Feb. 19, 2020 (American Heart Association News) -- Red dresses and pink ribbons have helped millions of Americans become aware of the separate tolls heart disease and breast cancer take on women. But not everyone is aware of how the illnesses can intersect.

Heart disease – the No. 1 killer of women – can sometimes be a complication of breast cancer treatment. Older women who survive breast cancer are more likely to die of heart disease than a cancer recurrence.

Dr. Laxmi Mehta, who led the writing of a wide-ranging 2018 report from the American Heart Association on the two diseases, said the overlap exists on a spectrum.

Sometimes, cancer directly causes heart problems, such as when it causes fluid buildup around the heart. Much of the time, though, the problem comes from treatments targeting cancer.

Radiation therapy for breast cancer can lead to blocked heart arteries, heart valve issues and abnormal heart rhythms in some patients, Mehta said. She is professor of cardiovascular medicine and director of preventive cardiology and women's cardiovascular health at The Ohio State University Wexner Medical Center in Columbus. Chemotherapy and other cancer treatments can weaken the heart and lead to blood clots, high blood pressure and other issues.

Some issues show up soon after treatment, Mehta said. Others show up years down the line. These heart issues led to an emerging field called cardio-oncology to protect heart health while still providing the best cancer care.

Heart issues also can get in the way of treating breast cancer in some women.

"If they get a weakened heart muscle, in some people that means they have to stop treatment for a while until the heart recovers," Mehta said. "Or, in other people, it might mean you can't have that treatment at all."

That can be emotionally taxing on a patient and her care team. "They're already psychologically under a lot of stress with cancer treatment, and now we're telling you, 'By the way, your heart is a problem.' Many patients will say, 'I don't care about my heart – just fix the cancer now!'" But both problems have to be addressed, she said.

The connection isn't all bad news.

Heart disease and breast cancer share some risk factors, so lifestyle measures can help prevent both, said Dr. Debu Tripathy, professor and chair of the department of breast medical oncology at the University of Texas MD Anderson Cancer Center in Houston.

"The data is compelling enough that adopting the heart-healthy approach in terms of exercise and diet is good for both heart and breast cancer health," whether you're talking about preventing or surviving the conditions.

One way diet affects both diseases has to do with cells' energy needs, Tripathy said.

"We all have pre-malignant cells in our body that are moving toward cancer," he said. The immune system and other protective mechanisms fight a constant battle against these cells, either by tricking them into committing suicide or destroying them. "Every now and then the body gets overwhelmed, and that's when you get cancer."

But a healthy diet may provide backup to the immune system, preventing the pre-malignant cells from getting the extra energy they need to survive as cancer cells, he said. The excess energy also affects other processes such as inflammation and fat metabolism, which play a role in heart disease.

If diet and exercise are important for prevention, they remain important for people who have breast cancer, Mehta said.

Many people with cancer think they need to rest, she said. "And with chemo there are going to be days where it just drags you down and you can't exercise. But the other days that you have some energy, just any little bit of physical activity – it's not, 'Go run a mile' or anything – is so good for you."

So is eating right.

"Many people just feel like, 'I can just eat whatever I want. I'm on chemo,'" she said. "And that sometimes is necessary, because sometimes a lot of things aren't palatable when you're undergoing chemo. But when your appetite is better, you want to make sure you're trying to eat heart-healthy as best as you can."