Many diseases and medical conditions are caused by things out of our control. Yet experts say you can control and even prevent many of the risk factors that increase your chances of dying.

An unhealthy lifestyle can put you at great risk of heart disease and stroke（中风）.Poor diet, having too much body fat and being short of physical exercise all increase your risk of heart disease —so can smoking and drinking too much wine. So doctors suggest we eat healthy foods, get exercise, stop smoking and drink less.

But there is something else you can do. And it is free and easy. Smile!

Anand Chockalingam is a heart disease specialist at University of Missouri Health Care in Columbia, Missouri. He advises his patients to smile. He says smiling is a first step in fighting stress and its sometimes harmful effects on human health.

When you feel stressed or under pressure, your body lets out many natural hormones（荷尔蒙）.If you are truly in danger, these hormones can help you. However, when people are stressed for long periods of time, they may not make the best decisions about what to eat. They may overeat, smoke or drink too much. They may not get enough exercise or sleep. And all of these can lead to health problems.

Dr. Chockalingam says a smile may be one way to help. He tells his patients to smile 20 times an hour. To some, that might seem like a lot of smiling. Or some might even feel foolish — smiling for seemingly no reason. But a smile does not need drugs. It does not leave cuts like an operation. It is free and it has no bad side effects.

“Once people smile, they are relaxing, which directly lowers blood pressure, improves sugar levels in the blood. If we are smiling, we are breaking that link between stress and health.”

And it just may provide a little extra protection to everyone's heart health.

Could being a little overweight help you live longer? A new international analysis (分析) shows a surprising answer: while obesity (肥胖) increases the risk of dying early, being slightly overweight reduces it. These studies included almost 3 million adults from around the world, yet the results were clearly the same, the authors of the analysis said.

“If you have a medical condition, your chances, of living are slightly better if you are a bit on the heavy side,” says study author Katherine Flegal, “Several factors may contribute to this finding.”

“Heavier people may tend to see the doctor earlier,” she says, “and may be more likely to be treated according to the doctor’s advice. Obesity itself may protect the heart, or someone who is heavier might be better able to fight against a shock to the system.”

For the study, Flegal’s team collected data on more than 2.88 million people included in 97 studies. The researchers looked at the participants’ body mass index (BMI), a measure of body fat that takes into consideration a person’s height and weight.

The researchers found that, compared with people of normal weight, overweight people had a 6 percent lower risk of death. Obese people, however, had an 18 percent higher risk. For those who were the least obese, the risk of death was 5 percent lower than people of normal weight, but for those who were the most obese, the risk of death was 29 percent higher, the findings showed.

While the study found a relation between weight and the risk of early death, it did not prove a cause-and-effect relationship. Indeed, one expert warned that body weight alone cannot tell health and the risk of death.

“There are other factors that play a role in health,” says Dr. William, a professor at Louisiana State University. “BMI simply is a parameter (参数); it doesn’t take family history, smoking, fitness, and other factors into consideration.”