Twinning rates: Reply

Abstract

Sir, I was pleased to note that my honoured colleague Professor emeritus Björn Westin still recalls my old studies on the impact of light on reproduction 1. I once thought that this topic effect could be accentuated in high latitudes, e.g. in Northern Finland, where the daylight shows a huge variation between the autumn–winter (‘endless night’) and spring–summer (‘endless day’). We were able to show a significant relation between the duration of daylight and rates of conception and twinning 2. Later, my contemporary, the late Professor Olof Widholm, an honorary member of NFOG, explored the impact of daylight on the initiation of menarche. Menarche showed two peaks, one in light June and another at the dark Christmas time. Apparently, it was not only the light but also the relaxing effect of school vacation that triggered the initiation of menarche. Obviously, in later years, we have moved far away from the natural way of living. Electricity everywhere has ceased endless nights, and women are no longer exposed to pregnancy ‘naturally’, but are now using different forms of contraception. In addition to social factors, light may still have some impact on conception through the endocrine system. Professor emeritus Antti Kauppila in Oulu University later showed that the output of melatonin from the pineal gland peaked with the darkest season, and this should suppress the gonadal function. Our research was based on material from the period 1960–1964 3, 4. Exposure to light was measured by the number of sunshine hours every month from 1960 to 1964, according to the monthly reports of the Meteorological Central Office of Finland. The number of sunshine hours from various parts of Finland was combined and the mean of the whole country was used as an indicator. The φ2-squared test (4-fold table) was used for statistical significance. I am now 92 years and in good health. I am very pleased to see how much Acta has progressed, and no wonder, when modern research offers so much to interested readers. I wish Acta all the best for the future.