Canadian infants appear to have some of the highest levels of colic in the world, according to a new study that attempted to create the first international “crying chart” to determine why some babies cry more than others.

Colic has long been defined as infant crying that lasts longer than three hours a day for at least three days a week. For parents who can’t comfort their child with the usual rocking, swaddling, or diaper-changing, the unexplained crying of colic can become heart-wrenching.

To try to understand where colic levels are highest, researchers at the University of Warwick reviewed 28 previous studies on infant crying that involved close to 8,700 infantsfrom eight countries whose parents kept diaries of their babies’ crying habits.

They found that in Canada, 34.1 per cent of babies have colic by age three to four weeks old. In the U.K., 28 per cent of infants meet the threshold of colic at age one to two weeks old. And in Italy, 20.9 per cent had colic around age eight to nine weeks.

Denmark, on the other hand, has one of the lowest rates, with only 5.5 per cent of babies aged 3 to 4 weeks meeting the definition for colic. Germany also had low colic rates, of only 6.7 per cent at 3 to 4 weeks.

Dieter Wolke, the study lead author and a professor in Warwick’s department of psychology, says the average four-week-old baby cries for about two hours a day.

“In Canada, babies cried on average for 30 minutes more, so 2-1/2 hours a day,” he told CTV News Channel from Munich.

But he also noted that babies varied greatly in how much they cried in their first few weeks of life.

“Some babies cried for as little as 30 minutes and some cried for as much as five hours,” he said.

The study authors said it’s not clear why colic rates might be higher in some countries than others.

“We can only speculate on the reasons why there are country differences, in particular between Denmark and the rest of Europe and North America,” they write.

These differences could range from economic conditions, such as less social inequality, to caretaking patterns such as responsiveness or carrying behaviour. There may also be genetic differences at play, they said.

It’s also possible that certain cultural differences might have influenced the accuracy of the diary keeping, the authors note, since parents’ perception of the frequency of their infants’ crying might vary by culture.

Wolke says one important thing for parents to note is that often babies cry for reasons that no parent can understand. For example, his team has found that about 40 per cent of the crying in a baby’s first few months was inconsolableand couldn’t be stopped no matter what parents did. That was found everywhere from Canada to Denmark.

“I think an important takeaway is that we always look to the parents that they are doing something wrong. Our findings don’t suggest that,” he said.

The full study is published in The Journal of Pediatrics.