Additional Confirmation for the Effect of Environmental Light Intensity on the Seasonality of Human Conceptions

Abstract

Causality for the seasonality of human births, which affects populations wordwide, has been a profound mystery for nearly two centuries. Most explanations for seasonality fail because of inconsistent global application. In two previous studies, Cummings (2002, 2003) hypothesized that human reproduction has been responsive to changes in both seasonal environmental light intensity (surface luminosity) and photoperiod. Except at higher latitudes, photoperiod is of secondary importance to that of environmental light intensity. Because of a lack of data, the presence or lack of cloud cover is used as a general proxy for environmental light intensity. These studies show a positive correlation between conceptual seasonality and cloud cover on a worldwide basis, and propose that there is a delay between exposure to increased light and the onset of conceptions. This delay is three months at higher latitudes and one to two months for lower latitudes. Both studies suggest that an excellent means of hypothesis confirmation would be to provide one or more examples of how a seasonal change in cloud cover might alter the number of conceptions in subsequent months. The present study tests this hypothesis. The percentage of possible sunshine and averaged sunshine hours are used to investigate their influence on seasonality of births in Germany and the Netherlands. The evidence shows that a seasonal change in environmental light intensity preceded a change in the peak months for conceptions in Germany and the Netherlands. Although secondary influences are possible, the primary reason for this transition in peak conceptual months seems to be related to the seasonal changes in environmental light intensity for both countries. Although this transitional relationship was predicted in Cummings (2002, 2003), further research is required, especially with regard to more precise measurements of environmental light intensity and its physiological effect on the human endocrine system.

Birth Seasonality in Present-Day Italy, 1993–2005

“…Although there is no general agreement on the influence of climatic factors (Bronson 2004a), studies outside Italy provide evidence that temperature Myron 1991, 1996;Madrigal 1993;Werschler and Halli 1992), length of photoperiod (Roenneberg andAschoff 1990a, 1990b;Rojansky et al 1992), light intensity (Cummings 2007), and, under specific conditions, the amount of rain (Bailey et al 1992) could account for the seasonal birth profile within communities and populations, even in presence of profound social and economic transformations (Doblhammer et al 2000). For instance, neither the demographic transition, in particular in the United States (Shimura et al 1981), nor the introduction of contraceptives (Shiver 1985) would seem to have introduced significant changes in birth seasonality.…”

Seasonality updated in 28 European/Mediterranean countries: A continuing enigma

“…Subsequent research (Cummings, 2007(Cummings, , 2009) involving sunshine hours and the percentage of possible sunshine confirmed that as the ambient atmosphere changed so did conceptual seasonality change in Germany, The Netherlands, England, Wales, and Scotland. Essentially, spring months became cloudier, autumn months slightly sunnier and peak conceptions slipped into late summer/early autumn.…”

Daily, monthly and seasonal variation in PSA levels and the association with weather parameters

“…Sexual behaviour in humans does show seasonal variation. [13][14][15][16][17] This is apparent in many European countries, 13 with peak conception rates occurring in April/May. Conception rates also correlate with increasing exposure to sunlight and with temperature.…”

“…Conception rates also correlate with increasing exposure to sunlight and with temperature. 14,15 Further, the frequency of sexual activity, rate of sexually transmitted diseases and the sale of contraceptives are all seasonal, 16 with Carlsen et al 17 demonstrating higher rates of ejaculation during springtime in Danish men. Therefore, seasonal variation in PSA levels may be a reflection of the variation in ejaculation frequency in the studied populations.…”