Our bodies are wonderfully skilful at maintaining balance. When the temperature jumps，we

　　sweat to cool down. When our blood pressure falls，our hearts pound to compensate. As it turned

　　out，though，our natural state is not a steady one. Researchers are finding that everything from

　　blood pressure to brain function varies rhythmically with the cycles of sun，moon and seasons.

　　And their insights are yielding new strategies for keeping away such common killers as heart disease

　　and cancer. Only one doctor in 20 has a good knowledge of the growing field of “chronotherapeutics

　　”，the strategic use of time(chronos)in medicine. But according to a new American Medical

　　Association poll，three out of four are eager to change that.“The field is exploding”，says Michael

　　Smolensky.“Doctors used to look at us like‘What spaceship did you guys get off?’ Now they’re

　　thirsty to know more.”

　　In medical school，most doctors learn that people with chronic conditions should take their

　　medicine at steady rates.“It’s a terrible way to treat disease.”says Dr. Richard Martin. For example，

　　asthmatics(氣喘患者)are most likely to suffer during the night. Yet most patients strive to

　　keep a constant level of medicine in their blood day and night，whether by breathing in on an inhaler

　　(吸入器)four times a day or taking a pill each morning and evening. In recent studies，researchers have found that a large mid-afternoon dose of a bronchodilator(支氣管擴(kuò)張劑)can

　　be as safe as several small doses，and better for preventing nighttime attacks.

　　If the night belongs to asthma，the dawn belongs to high blood pressure and heart disease.

　　Heart attacks are twice as common at 9 a.m. as at 11 p. m.. Part of the reason is that our blood

　　pressure fails predictably at night，then peaks as we start to work for the day.“Doctors know that

　　”，says Dr. Henry Black of Chicago’s Medical Center，“but until now，we haven’t been able

　　to do anything about it.”Most blood pressure drugs provide 18 to 20 hours of relief. But because

　　they’re taken in the morning，they’re least effective when most needed.“You take your pill at 7

　　and it’s working by 9，”says Dr. William White of the University of Connecticut Health Center，

　　“but by that time you’ve gone through the worst four hours of the day with no protection.”Bedtime

　　dosing would prevent that lapse，but it would also push blood pressure to dangerously low levels

　　during the night.