Birth month may influence more than we think

Good and bad news: I may not have been totally psycho for being a bit paranoid about what month my baby is being born in. They don’t seem to find a correlation between overall life success, though, so we’re still in the clear:

*edit* Yes, I realize a lot of the results of these studies may have other causes than what season you were born in, but it’s still an interesting exercise…

If you don’t believe in horoscopes, you’re in step with science. But that’s not the same as saying the season of your birth cannot affect your fate. Hundreds of studies, published in peer-reviewed journals, have suggested that the month a person is born in is associated with characteristics such as temperament, longevity and susceptibility to certain diseases.

Scientists say that even though some of these findings are probably spurious — if you dig around in data, you will eventually find correlations just by chance — other effects are very likely real, triggered not by the alignment of the planets but by exposures during prenatal and early postnatal lives.

Temperature, sunshine, seasonal foods, winter infections: All can affect the development of a baby and, as a result, its future. Here’s a look at the findings and what scientists make of them…

Summer (June 22 to Sept. 22)

Sleep habits: Studies find that people whose birthdays fall in June to September are more likely to be evening than morning types when compared with those born in winter. A survey of 5,720 European students published in 2009 in the journal Sleep showed that those born in August went to bed 19 minutes later on average than December-borns. Study lead author Vincenzo Natale of the University of Bologna, Italy, argues that our internal clocks are set for life when we are born. Here’s how he thinks it works: In the summer, abundant sunlight influences the maturing of the brain’s circadian clock, setting it to a pattern of longer days. Experiments on mice support this theory, as does the finding that in Australia the patterns are shifted by six months. But the tendency to be an owl or lark is also strongly influenced by genes, Natale notes: “If someone genetically predisposed to being an evening type is born during summer, he will become an extreme evening type, but if he’s born in winter, he will end somewhere in between an evening and a morning type.”

Handedness: Summer- and spring-borns are more likely to be left-handed. A study published in 1994 in the journal Perceptual and Motor Skills examined handedness among males conscripted to the French army, male American baseball players and data collected by the U.S. Bureau of the Census and the National Center for Health Statistics. It showed that 41.2% of all left-handed people were born in the five months from March to July, but only 38.2% of all right-handed people. According to psychology professor Maryanne Martin (University of Oxford) and Gregory Jones (University of Warwick), authors of a 1999 study that confirmed these results, it’s not yet clear why such differences exist; possible factors include variations in maternal nutrition or exposures to sunshine, temperature or seasonal infections, such as flu or measles, during the second trimester of pregnancy.

Diabetes: Children born in summer (especially in August) are more likely to develop Type 1 diabetes, in which the body’s immune system kills off the cells in the pancreas that secrete insulin. This was shown in a 1999 study of Swedish children published in the Archives of Disease in Childhood. In a sample of 1,248 children with diabetes, there were 24 patients more than expected born in August and 33 less than expected born in October. Again, viral infections may be why: Mouse studies have shown, for example, that coxsackieviruses disturb the immune system and can induce diabetes.

Read about all the seasons: That bad attitude? Blame the birth month

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