Parents and caregivers are encouraged to place infants on their backs at night and nap time. (U.S. Consumer Product Safety Commission)

Babies are more likely to die of sudden infant death syndrome on New Year's than other days of the year, a new study suggests.

The reasons are not clear but researchers suspect that parents who celebrate the new year with heavy drinking aren't being attentive enough to their children and how they're put to bed.

The researchers examined a large U.S. database to explore connections between alcohol and SIDS — the sudden, unexpected death of an apparently healthy infant under one year of age.

The spike in deaths is beyond the normal winter increase in SIDS, sociologist David Phillips of the University of California, San Diego, and his co-authors report in this week's issue of the journal Addiction. They analyzed a database of 129,090 deaths from SIDS from 1973 to 2006 and 295,151 other infant deaths in those years.

The study doesn't give actual figures for the New Year's Day deaths from SIDS but said the number was about a third higher than would be expected on any other winter day.

To see if parental sleeping-in might be a factor rather than intoxication, the researchers checked for shifts in deaths when clocks are set back an hour in the fall. No rise in SIDS was found then.

The study doesn't show alcohol consumption is a cause of SID, but the findings raise concerns, Phillips said. Drunk parents could be doing something or not doing something that puts babies at risk, he suggested.

Impaired judgment?

"We know that when people are under the influence of alcohol their judgments are impaired and they are not as good at performing tasks," Phillips said in a release. "This would include caretaking."

Single-day jumps in cribs deaths occurred on July 5, the day after Independence Day.

Back to Sleep campaigns that recommend parents and caregivers place infants to sleep on their backs at night and nap time have been successful, the researchers noted.

"A similar campaign might now be implemented: There should be increased efforts to inform caretakers that alcohol impairs parental capacity and might be a risk factor for SIDS," the study's authors wrote.

The Public Health Agency of Canada also advises parents to lower risk of SIDS by:

• Not smoking around the baby.
• Avoiding dressing the baby in too many clothes or adding too many covers to prevent overheating.
• Providing a safe crib environment that has no toys or loose bedding.

A second study by Phillips that analyzed mortality rates for the U.S. population found people are more likely to die during the Christmas season.

The analysis of U.S. death certificates between 1979 and 2004 found that in the two weeks starting with Christmas there were 42,325 natural deaths above the usual seasonal winter increase.

Again, the reasons are unknown. Possible explanations for the spike in deaths include overcrowding in emergency departments, winter travel, cold weather and substance abuse, the researchers said.