Warmer climates favour the birth of boys

Declining male births with increasing geographical latitude in Europe 2000;54:244B6

Warmer climates favour the birth of boys, shows a study in the Journal of Epidemiology and Community Health.

Researchers analysed all recorded births by sex in Malta between 1890 and 1995, and for the whole of Western Europe between 1990 and 1995. The Maltese data did not support evidence of a decline; if anything the ratio of boys to girls was significantly higher than expected. Analysis of the birth data for Mediterranean, Central European, and Scandinavian countries showed that the birth of boys was strongly associated with climate. The greater the latitudeCand the colder the climateCthe lower was the birth rate for boys.

Studies show that the number of male births in several industrialised countries has fallen during the second half of the twentieth century. This may be because male babies are less robust than their female counterparts and more susceptible to the effects of toxins or other environmental factors, say the authors. But there is no obvious explanation, they say, for the higher numbers of boys born in Southern Europe than in Northern Europe, other than temperature. "Ambient temperatures may not only affect fertility," they conclude, "but may also influence sex ratios at birth."

Contact:

Dr Victor Grech, Department of Paediatrics, St Luke's Hospital, Guardamangia, Malta. victor.e.grech@magnet.mt