While people groan and mumble about lost sleep with the "spring forward" of daylight saving time, there can be even harsher effects, U.S. researchers say.

One study by Stanford University and John Hopkins University reported more fatal traffic accidents the Monday after the time change, The Miami Herald reported.

In 2008, Swedish researchers said there was a 7 percent increase in heart attacks the Monday after spring's daylight saving switch.

Even animals seem affected, as Indiana dairy farmers say having to milk their cows an hour earlier caused the animals to lose sleep and produce less milk.

However, one sleep researcher says the 1-hour difference really shouldn't be a big problem.

"One hour is very tolerable, and most of us are able to adapt," Dr. Alejandro Chediak, director of the Miami Sleep Disorders Center, said. "It's when you start dealing with 2 or 3 hours less of sleep that it becomes very noticeable."

The fall and spring dates of daylight saving time have moved over the years. The dates were formerly in April and October, but moved to the second Sunday in March and the first Sunday in November under an energy bill signed into law in 2005 by President George W. Bush.

Daylight saving time will begin at 2 a.m. Sunday.