When health experts calculate the likelihood of someone having a heart attack, they typically look at well-known risk factors including high blood pressure, smoking, a sedentary lifestyle and a family history of early heart disease.

What most people don’t realize: There are “secret” or little-known risk factors for heart attack that most people (including most doctors) ignore. Many of these factors are as risky as the well-known ones above. Here are the secret risk factors for a heart attack…

AN INTENSE SPORTS LOSS

Researchers in Los Angeles tracked causes of death in the counties or states of teams playing in the “high drama” 2008 and 2009 Super Bowls—the New York Giants beating the New England Patriots (Massachusetts) in 2008…and the Pittsburgh Steelers beating the Arizona Cardinals in 2009. The researchers found that in the eight days starting on the day of New England’s loss, the number of deaths from heart disease in Massachusetts was 24% higher than it had been after previous Super Bowls…and in the eight days starting on the day of Pittsburgh’s win, the number of deaths from heart disease in the Pittsburgh area was 31% than it had been after previous Super Bowls. Meanwhile, in Arizona, where researchers had established that fan fervor for the home-state team was significantly lower than in Massachusetts and Pittsburgh, there was little ­difference in the rate of heart disease deaths after the team’s loss. (Data could not be obtained from New York City.)

The disappointment of a losing game after fervently rooting for a team is a form of emotional stress, which can trigger heart attacks—possibly because stress hormones increase heart rate and blood pressure and make blood more likely to clot. (The researchers didn’t theorize about what caused the decrease in the death rate in Pittsburgh after its win.)

But forlorn fans aren’t the only folks whose hearts are harmed by emotional stress. Research shows that other events that cause emotional stress—holidays such as Christmas and New Year’s…a nearby natural disaster…daily problems at work…or the recent death of a spouse—increase the risk for heart attacks. So does the emotional stress of acute anger, chronic hostility and pessimism.

Smart strategy: The risk from emotional stress can be dramatically reduced by regular exercise (see below).

AIR POLLUTION

Tiny particles of air pollution—congealed specks of floating carbon, metals and other “particulate” ­substances that emanate from exhaust pipes, ­industrial smokestacks and coal-fired power plants—cause heart attacks. In fact, in a scientific statement released in 2010, the American Heart Association said that just hours of exposure to these particulates can trigger heart attacks and that long-term exposure increases risk even more.

The people most at risk for heart attacks from air pollution have other risk factors for heart disease—they are over age 60, overweight, have diabetes and/or have had a previous heart attack or stroke. But years of exposure to air pollution can increase the risk for heart attack for any senior.

Scientific evidence: A new study published in Environmental Research shows that even a few years of low exposure to air pollution in a city increased the risk of developing heart disease in older people by more than 20%.

Bottom line: Make air pollution less risky to your heart by working with your doctor to reduce other risk factors such as being overweight or having high blood pressure, high LDL cholesterol and high blood sugar.

Also, know when the air is unhealthy, and stay indoors at those times. ­Resource: AirNow.gov, which displays daily air-quality levels across the US.

Eat fatty fish two to three times a week or take a daily fish oil supplement for the omega-3 fatty acids. New research: Harvard Medical School ­scientists found that boosting blood levels of omega-3s can prevent the ­artery-damaging inflammation caused by air ­pollution.

MARIJUANA

In a study of nearly 4,000 people published in Circulation, researchers found that smoking marijuana caused a five-fold increased risk for heart attack during the first hour after smoking. In a similar study of nearly 2,000 people published in American Heart Journal, those who used marijuana weekly or more often had four times the risk for heart attack and nearly double the risk of dying from heart disease, versus people who didn’t use marijuana at all.

Reason: The autonomic nervous system controls your heart’s activity, and marijuana delivers a one-two punch to both parts of the autonomic nervous system. It stimulates the sympathetic nervous system, speeding up heart rate and raising blood pressure (making a heart attack more likely)…while suppressing the heart- and artery-relaxing parasympathetic nervous system (also putting you at greater risk for a heart attack).

Bottom line: Avoid using recreational marijuana if you have risk factors for heart disease. If you’re using it ­medicinally, discuss the risk with your doctor.

ERECTILE DYSFUNCTION

Heart attacks occur when people develop atherosclerosis—a blockage of one or more coronary arteries by cholesterol-ridden arterial plaque. And one common sign that an older man has such blockage is erectile dysfunction (ED)—a problem often caused by a blockage of blood flow to blood vessels in the penis.

Compelling scientific evidence: Research shows that ED precedes the symptoms of heart disease (such as chest pain) in seven out of 10 men with heart disease—with ED usually showing up about three years earlier. And a study published in International Journal of Impotence Research shows that severe ED nearly triples the risk for heart disease.

Bottom line: The scientific consensus is that a diagnosis of ED is a warning of heart disease. If you are diagnosed with ED, you should have a cardiovascular workup—as soon as possible.

THE EXERCISE ELIXIR

The human cardiovascular system is designed for daily physical activity. Physical activity helps keep blood pressure normal…blood sugar stabilized…cholesterol low…the heart muscle strong…and the risk for heart attack minimized—including the risk from little-known risk factors. In my view, exercise is the best habit for your heart.

Compelling scientific research: In an eight-year study of more than 400,000 people published in The Lancet, researchers found that even 15 minutes of daily exercise reduced the risk of dying by 14%—and that includes the risk of dying from cardiovascular disease. And those 15 minutes don’t even have to be continuous. To get the benefit, you can exercise for five minutes, three times a day.

My advice: Brisk walking is an ideal exercise. You can do it easily with others, which further reduces your risk for a heart attack. (Social isolation and loneliness increase the risk for heart disease by 29%, according to a recent study published in Heart.) And you can build walking into your other daily activities—such as parking five to 10 minutes away from your destination and walking the rest of the way.