It doesn't take a scientist to understand that laughter feels good, while anger feels awful.

But it does take one to explain why one of these feelings can boost the immune system, while the other can wear it down, damage the heart and increase the risk for dementia.

Simply put: "Mood can influence your health," said Dr. Erin Michos, director of Women's Cardiovascular Health at Johns Hopkins School of Medicine in Baltimore.

Studies show negative emotions—including anger, hostility and pessimism—are linked to a higher risk of heart disease and lower chance of recovery from events such as heart attacks, as well as poorer cognitive health. Conversely, a growing body of research shows feelings such as happiness, optimism, gratitude, a sense of purpose, well-being or satisfaction in life lead to better heart and brain health. A 2016 study in Health Psychology even found that having a happy spouse or partner could improve an individual's overall health and increase healthy behaviors, such as being more physically active.

There are many reasons for this, said Michos, a cardiologist who co-authored a recent American Heart Association scientific statement on the ways in which psychological health impacts heart and brain health.

Strong, negative feelings, such as anger, and stress, such as from anxiety or depression, activate the amygdala, the region in the brain that handles emotion. It activates the body's "fight or flight" response, triggering the release of cortisol and adrenaline, hormones that make the heart beat faster and blood pressure rise, she said. "This can be stressful on the heart, particularly for people who have underlying heart conditions."

It also can cause blood platelets to form clots, and trigger plaque in the heart or brain to rupture, causing a heart attack or stroke. Prolonged stress also increases inflammation and lowers the body's immune response.

This biological response may be compounded by harmful behaviors, Michos said. "People with poor coping mechanisms for stress may sleep poorly, engage in binge eating and exercise less."

On the flip side, lowering stress through positive feelings also affects brain circuitry, said Jill Goldstein, founder and executive director of the Innovation Center on Sex Differences in Medicine and professor of psychiatry and medicine at Harvard Medical School in Boston.

Mindfulness, humor and other mental coping skills can help people stay healthier by reducing the amount of cortisol running through their bodies, she said. In women, this can protect the production of estradiol, a type of estrogen that can be important for preserving good brain health

"We are also enhancing our immune systems when we help regulate the stress response," she said. "The brain talks to the body and calms the body down. It slows your breathing and your heart rate. Some people are better able to do this than others."

But it's not just the absence or reduction of stress that gives the brain what it needs to coordinate better overall health, Michos said. "Well-being is more than the absence of mental distress," she said. "Happiness, optimism, a sense of purpose, gratitude, mindfulness—these are all associated with favorable heart health, even independently of a lack of negative factors."

And research shows anything good for the heart is good for the brain.

Michos said people don't have to be naturally cheery or easygoing to reap these benefits.

"Some of this can be learned," she said. "You can cultivate positive thinking and mindfulness and coping mechanisms to deal with adversity."

Staying physically active also helps to boost mood, she said. So does spending time with friends and family to build strong social support.

The better someone feels, the more likely they are to maintain their health, Michos said. "Optimistic people take better care of themselves. They are more compliant with medication, more likely to get checkups, to eat healthy and exercise."

It's never too late to make a difference, said Goldstein. "The brain is very retrainable. The older we get, the more difficult it is to do, but it can be done."