If you’ve been blessed with good genes, your lifestyle and environment may be the ultimate determinants of your health. If you’ve inherited a gene that increases your susceptibility to a certain disease, your lifestyle and environment may increase or decrease your risk of ultimately developing that disease.

The number of such factors that may figure in to your health and longevity is infinite, but you can significantly reduce your risk of a number of life-threatening illnesses by following these three important recommendations.

Don’t smoke.

The single most preventable risk factor for heart disease and stroke is tobacco usage. Although no one knows for sure exactly how tobacco smoke causes heart disease or increases the risk of stroke, smoking has been shown to raise blood pressure and contribute to the development of atherosclerosis. People who smoke have a risk of heart disease two to four times higher than people who don’t. Smoking also increases stroke risk by 40 percent in men and 60 percent in women. The good news is that quitting can rapidly reduce your risk of heart disease and stroke. Three years after you quit, your risk of heart disease is almost the same as that of a nonsmoker. Stroke risk declines to that of a nonsmoker within two to five years.

Smoking is also responsible for most lung cancers, and tobacco use contributes to oral, throat, and esophageal cancers. Smoking is also the leading cause of COPD. In fact, 82 percent of those who die of COPD are smokers.

Smoking is also linked to an increased risk of dementia, asthma, hearing loss, and macular degeneration (a leading cause of blindness). All told, smoking contributes to approximately 500,000 deaths a year, according to the Centers for Disease Control and Prevention.

Maintain a healthy weight.

As many as 97 million Americans are considered overweight. Excess weight—especially around the abdomen—is associated with an increased risk of heart disease. But losing as little as 10 pounds can make a difference. Studies show that in overweight people with high blood pressure, losing weight enhances the blood pressure-lowering effect of medications, reduces high cholesterol levels, and reduces the need for medications.

Gaining weight as you age may also increase your risk of cancer. A study that monitored the health of 95,000 nurses for 16 years found that those who gained weight since age 16 had a higher likelihood of developing breast cancer. Most at risk were postmenopausal women who gained 44 to 55 pounds—their risk was increased by as much as a 40 percent.

Being overweight is also associated with an increased risk of diabetes. Up to 90 percent of those with type 2 diabetes are overweight.

Be physically active.

Exercise strengthens the heart and lowers heart rate and blood pressure. The American Heart Association (AHA) suggests a minimum of 30 to 60 minutes of moderate-intensity aerobic activity three to four times a week, augmented with an increase in lifestyle activities such as taking a walk during your break or using the stairs. Researchers at Brigham and Women’s Hospital in Boston found that men who exercised 11 to 24 minutes twice a week reduced their risk of heart attack by 36 percent. Those who did five workouts weekly reduced their risk by 46 percent. And researchers from the Harvard School of Public Health recently reported that an hour of moderate exercise five days a week may lower the risk of stroke by 46 percent.

Exercise is also linked to a reduced risk of cancer and diabetes. In fact, some researchers have blamed the upsurge in diabetes cases on Americans’ lack of exercise. Thirty minutes of cumulative exercise daily helps maintain proper glucose levels in the blood. Aerobic exercises such as walking, swimming, and bike riding appear to be most effective at controlling glucose levels.