Sun children are bigger
There is a clear connection between the height of an adult male and his month of birth. Spring babies are usually larger than children born in autumn, the annual high is in April, the lowest in October. Such claims can, of course, only be confirmed by an enormous amount of data. Scientists therefore evaluated the statistics of the Austrian Federal Army. Gerhard W. Weber and his colleagues from the University of Vienna reported in Nature on February 19, 1998 what their review of over 500,000 height and birth records revealed. Due to the compulsory military service in Austria, the federal army there has the necessary statistics for every 18-year-old male Austrian. Weber and his team had access to measurements for all men born between 1966 and 1975; 507 in total.125 records.
First of all, the researchers noticed that the average Austrian tended to get taller in general, but this trend was subject to a clear annual rhythm, with highs occurring in spring and summer births and lows in autumn and winter babies.
This clear annual trend, the scientists argued, must be caused from outside. Therefore, they studied weather records, which show how often there was a bright sky in Austria. As expected, the country gets the most sun in July and the least in December. Birth rates and sunshine duration vary within an annual cycle, but have their peaks and troughs at different times. Interestingly, the maximum values for births are always 276 days behind those for maximum solar radiation. This corresponds exactly to the duration of pregnancies. Summer conceived and spring born tend to be the tallest adults. So is there a connection between what happens in a child's development and the amount of sunshine that shone on the mother?
Agreement does not necessarily imply a cause and effect relationship. For example, there is a well-known correlation between the birth rate in the "old" Federal Republic and the number of white storks breeding there. Birth rates declined in line with stork abundance - but this does not mean that babies are born as gifts from storks.
Weber and his colleagues can only speculate about the causes of the observed trends. They don't focus so much on events early in pregnancy, but rather believe that the effect is due to events in the last trimester and the first few months after birth, when the child is growing most rapidly.
The underlying mechanism could have to do with the secreted hormone melatonin from the pineal gland. The pineal gland is hidden in the center of the head but has a neural connection to the eyes and responds to changing light levels by releasing more or less melatonin accordingly. Some researchers believe that melatonin may influence growth hormone behavior. Maternal melatonin passes through the placenta to the fetus, and the infant begins to produce its own melatonin as early as nine weeks after birth.
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