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October 13, 2015

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Study: women born in summer more likely to be healthy

Oct. 13, 2015
Courtesy of Elsevier journals
and World Science staff

Wom­en who were born in the sum­mer are more likely to be healthy adults, sug­gests new re­search. 

Au­thors of a study pub­lished in the jour­nal He­liyon, which in­volved al­most half a mil­lion peo­ple in the U.K., say more sun­light—and there­fore high­er vit­a­min D ex­po­sure—in the sec­ond tri­mes­ter of preg­nan­cy might ex­plain the ef­fect.

Ac­cord­ing to the stu­dy, birth month af­fects birth weight and when the girl starts pu­ber­ty, both of which have an im­pact on over­all health in wom­en as adults.

The en­vi­ron­ment in the womb leads to dif­fer­ences in early life—in­clud­ing be­fore birth—that can in­flu­ence health in lat­er life. This ef­fect, called pro­gram­ming, has con­se­quenc­es for de­vel­op­ment through­out child­hood and in­to adult­hood.

The re­search­ers be­hind the stu­dy, from the Med­i­cal Re­search Coun­cil Ep­i­de­mi­ology Un­it at the Un­ivers­ity of Cam­bridge, found that chil­dren who were born in the sum­mer were slightly heav­i­er at birth, taller as adults and went through pu­ber­ty slightly lat­er than those born in win­ter months.

“When you were con­ceived and born oc­curs largely at ran­dom—it’s not af­fect­ed by so­cial class, your par­ents’ ages or their health—so look­ing for pat­terns with birth month is a pow­er­ful study de­sign to iden­ti­fy in­flu­ences of the en­vi­ron­ment be­fore birth,” said John Per­ry, the lead au­thor.

Pre­vi­ous stud­ies have re­ported cer­tain ef­fects of the sea­son of birth, for ex­am­ple on birth weight and var­i­ous oth­er health out­comes. Per­ry and the team thought that child­hood growth and de­vel­op­ment, in­clud­ing the tim­ing of pu­ber­ty, is an im­por­tant link be­tween early life and lat­er health, so de­cid­ed to study more closely the im­pact of birth month.

The re­search­ers com­pared the growth and de­vel­op­ment of around 450,000 men and wom­en from the U.K. Biobank stu­dy, a ma­jor na­t­ional health re­source that pro­vides da­ta on vol­un­teers to shed light on the de­vel­op­ment of dis­eases.

The re­sults in­di­cat­ed that ba­bies born in June, Ju­ly, and Au­gust were heav­i­er at birth and taller as adults. The study al­so found that girls born in the sum­mer started pu­ber­ty lat­er, an in­dica­t­ion of bet­ter health in adult life.

“This is the first time pu­ber­ty tim­ing has been ro­bustly linked to sea­sonal­ity,” said Per­ry. “We were sur­prised, and pleased, to see how si­m­i­lar the pat­terns were on birth weight and pu­ber­ty tim­ing. Our re­sults show that birth month has a meas­ur­a­ble ef­fect on de­vel­op­ment and health, but more work is needed to un­der­stand the mech­a­nisms be­hind this ef­fect.”

The re­search­ers be­lieve that the dif­fer­ences be­tween ba­bies born in the sum­mer and the win­ter months could be down to how much sun­light the moth­er gets dur­ing preg­nan­cy, since that in part de­ter­mines her vit­a­min D ex­po­sure.

“We don’t know the mech­a­nisms that cause these sea­son of birth pat­terns on birth weight, height, and pu­ber­ty tim­ing,” said Per­ry. “We need to un­der­stand these mech­a­nisms be­fore our find­ings can be trans­lated in­to health ben­e­fits. We think that vit­a­min D ex­po­sure is im­por­tant and our find­ings will hope­fully en­cour­age oth­er re­search on the long-term ef­fects of early life vit­a­min D on pu­ber­ty tim­ing and health.”


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Women who were born in the summer are more likely to be healthy adults, suggests new research. Authors of a study published in the journal Heliyon, which involved almost half a million people in the U.K., say more sunlight—and therefore higher vitamin D exposure—in the second trimester of pregnancy could explain the effect, but more research is needed. According to the study, birth month affects birth weight and when the girl starts puberty, both of which have an impact on overall health in women as adults. The environment in the womb leads to differences in early life—including before birth—that can influence health in later life. This effect, called programming, has consequences for development throughout childhood and into adulthood. The researchers behind the study, from the Medical Research Council Epidemiology Unit at the University of Cambridge, found that children who were born in the summer were slightly heavier at birth, taller as adults and went through puberty slightly later than those born in winter months. “When you were conceived and born occurs largely at random—it’s not affected by social class, your parents’ ages or their health—so looking for patterns with birth month is a powerful study design to identify influences of the environment before birth,” said John Perry, the lead author. Previous studies have reported certain effects of the season of birth, for example on birth weight and various other health outcomes. Perry and the team thought that childhood growth and development, including the timing of puberty, is an important link between early life and later health, so decided to study more closely the impact of birth month. The researchers compared the growth and development of around 450,000 men and women from the U.K. Biobank study, a major national health resource that provides data on volunteers to shed light on the development of diseases. The results indicated that babies born in June, July, and August were heavier at birth and taller as adults. The study also found that girls born in the summer started puberty later, an indication of better health in adult life. “This is the first time puberty timing has been robustly linked to seasonality,” said Perry. “We were surprised, and pleased, to see how similar the patterns were on birth weight and puberty timing. Our results show that birth month has a measurable effect on development and health, but more work is needed to understand the mechanisms behind this effect.” The researchers believe that the differences between babies born in the summer and the winter months could be down to how much sunlight the mother gets during pregnancy, since that in part determines her vitamin D exposure. “We don’t know the mechanisms that cause these season of birth patterns on birth weight, height, and puberty timing,” said Perry. “We need to understand these mechanisms before our findings can be translated into health benefits. We think that vitamin D exposure is important and our findings will hopefully encourage other research on the long-term effects of early life vitamin D on puberty timing and health.”