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Adjusting to the daylight saving time switch can be toughest for night owls and people who are sleep-deprived.

For many Americans, the switch to daylight saving time is an annual rite of exhaustion. Gaining that extra hour of daylight at night means losing it in the morning. 

The time shift disrupts the body's natural circadian rhythm, according to sleep scientists. So the alarm clock blares just as your internal sleep-wake cycle orders you to stay snugly in bed. 

It's always harder to adjust to the "spring ahead" time change (as we did Sunday morning) than to the "fall back" change (on November 4), just as it's harder to fly east than west. Circadian rhythms are likely genetically determined and not fully understood. 

But research shows that the natural sleep-wake cycle is slightly longer than 24 hours. Therefore, "the circadian clock prefers us to extend our sleep in the morning when permitted," making it easier to stay asleep later than to fall asleep earlier, said Dr. James Wyatt, a specialist in sleep disorders at Rush University Medical Center in Chicago and a spokesman for the American Academy of Sleep Medicine.  

Genetic traits also determine your chronotype -- whether you are a night owl or a morning lark. Owls tend to have more difficulty with the daylight-saving shift, Wyatt said.

People vary greatly in their reactions to the sleep deprivation prompted by the time change.  Some 70 to 80 percent of people aren't significantly bothered, said Dr. Shyam Subramanian, director of the sleep center at University Hospitals Case Medical Center in Cleveland, and can adjust successfully in a day or two. Others yawn their way through the week.

For them, the consequences can be grave. Rates of workplace and traffic accidents, as well as of heart attacks, rise in the days following the spring time change. One study showed a nearly 6 percent rise in workplace injuries on the Monday after the daylight-saving switch. 

People already sleep-deprived are likely to have the toughest time. "With work, school, family and social obligations, most of us carry a chronic sleep debt into the weekend," Wyatt said. 

Wyatt and other researchers say people then spend the weekend trying to catch up. Even if they go to bed earlier, they can't easily fight their circadian rhythm. So they end up lying awake.

Though some argue that the time change is "just an hour," that amount of time is not insignificant, said Phyllis Zee, a professor at Northwestern University in Evanston, Ill., who is president of the Sleep Research Society. 

People who are nodding off will insist that they are "just resting their eyes," said Zee. "But the data shows they are impaired from an attention and safety standpoint. People are not aware of their level of impairment." 

Sleep experts suggest the following tips to dealing with the time switch:

• Perk up with coffee or another caffeinated beverage in the morning; avoid caffeine in the afternoon and evening.  
• Expose yourself to daylight soon after waking. Doing so helps adjust the circadian rhythm.
• Avoid bright light in the evening. Computer screens mimic daylight and throw your circadian rhythm off. 
• Practice good sleep habits, with a comfy bed, a quiet room and white noise to drown out sounds if necessary. 
• Be especially careful while driving or engaging in other activities requiring full alertness.