Stress and stress-related problems were considered epidemic in the 1980s and 1990s, and the start of the 21st Century has only seen the trend accelerate. The statistics beg the question: Why has modern life become so stressful?

Of course, stress is a natural response that helped our ancestors survive and prosper. For most of out history, the fight-or-flight responses triggered by stress were essential. When confronted by danger, the stress mechanism boosted blood pressure as well as blood sugar, and sent an increased blood flow to the brain to enhance our decision-making powers. Our muscle strength was boosted by an outpouring of adrenaline to give us more strength to fight off enemies. And under stress, blood coaulated more quickly to prevent us from hemorrhaging after an injury.

The problem is that today, almost all of our stress stems from psychological threats, not physical ones. As a result, the body's natural responses do us more harm than good. That's why, if repeated on a daily basis, stress can lead to high blood pressure, fatigue, muscle soreness and even depression.

How bad has stress become? A 1996 survey by Prevention Magazine found that 75 percent of Americans felt they were under "great stress" one day a week, and more that 30 percent said they were under stress twice a week.

And here's a startling statistic: An estimated 75 to 90 percent of all visits to a primary care physician are thought to be stress related. This is obviously a problem that must be dealt with if Americans are to live more comfortable, satisfying lives in the coming decades.

- Over 70% of initial visits to medical doctors are stress-related

- 62% say they end the day with stress-related work pain

- 40% of workers say their jobs are very stressful

- Mental and emotional stress is often connected to physical health problems

- Half of all college students have mental and emotional issues, struggling with the demands and pressure of school performance, relationship problems, coping with alcohol, money concerns, and general worry about life following college.