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October 20, 2022If you ever thought that your height is the result of your experiences, you were right. We know that height reflects changes in human health and well-being. We are taller than a century ago due to economic progress, improved living standards and advances in the welfare state.
We also know that this parameter reflects inequality. The differences of centimeters between affluent and low-income family backgrounds reflect a disparity in access to food, health and housing, including academic achievement.
However, it is less known that the month and season of birth can influence the growth of children and what their adult height will be.
A range of seasonal factors
Recent research shows that the effects of the month in which we begin to exist may be more important than we thought: the date of delivery is associated with maternal exposure, meteorological factors, air pollution, food supply, diet and physical activity.
Despite the methodological limitations of the research carried out, it can be seen that the date of birth is related, for example, to a marker of fetal exposure to vitamin D, associated with a wide range of health consequences, as we will see later. .
In recent decades, much research based on surveys and historical data from recruits has examined the influence of climate on the nutrition, living standards and height of children through their stunting, given that agriculture and food security are more affected by the climate crisis. This applies mainly to populations with low income and few resources.
However, studies on the impact of seasonality on final height are still scarce. The results have not always been consistent and are often even contradictory.
Advantages of being born in late summer and autumn
And although research does not identify a clear relationship between size and climate, it does suggest that the latter affects health in many ways. Currently, the frequency of extreme weather events and natural disasters disrupts food systems and causes diseases associated with malnutrition, malaria and heat stress.
A recent study, carried out by our research group at the University of Murcia and based on recruits from rural Spain throughout the 20th century, shows that those born at the end of summer and autumn recorded somewhat taller heights than those who came to the world in the winter months. September was the most favorable month in this regard. Furthermore, the study data is not socially biased, because it has been collected from a time when military service was mandatory for all men.
For Spanish populations born before 1970, employed mainly in the agricultural sector, not industrialized and little urbanized, the end of summer and autumn were the time of greatest agricultural yields, with availability of economic resources to provide animal proteins. The time for slaughtering pigs, a source of protein-rich food in rural homes, generally occurred in autumn.
The data suggests, therefore, that rural populations benefited at that time from access to fruits, fresh products and micronutrients necessary for growth. Furthermore, after the collection of fruits and the grape harvest in the months of September and early autumn, the family income necessary to purchase goods increased.
The findings are consistent with previous population-based studies from the past, both of German children from a strict military academy in the late 18th century, and of individuals born in low-income counties in western China.
Mothers who gave birth in summer and fall had access to plenty of food and fresh fruits and vegetables in late pregnancy, the period of greatest growth for the fetus. All of this suggests that harvests and agricultural yields and, therefore, food prices and income – basic for farming families – influence children's nutritional health.
The benefits of exposure to the sun and vitamin D
Another aspect to take into account is the amount of sunlight the mother receives before childbirth, which determines her exposure to vitamin D. Deficiency of this vitamin during pregnancy or childhood can delay the development of children.
Numerous studies indicate that it represents an important contribution to early postnatal growth. However, many clinical trials are still needed to demonstrate the possible risks of its deficiency on bone growth and development, as well as the supposed benefits of taking vitamin D supplements during pregnancy.
New research that includes women
Our group had already pointed out in previous studies the relationship between climate and size during Spanish industrialization. With this new stage of research we highlight the impact that the month of birth and climatic, monthly and seasonal cycles can have on our biological well-being and health.
On the other hand, now is the time to overcome the gender limitations of the research (which, by including only recruits, was based on male populations) and incorporate women into the studies. With the inclusion of more diverse populations and from different climates we will open the door to more complex relationships and findings on the relationship between climatic conditions and people's height.
Low-income and developing countries could be the most affected, given their dependence on the climate for resources and food. They are, once again, those who suffer the greatest consequences of climate change and its consequences on health.
Source: The Conversation. Authors: José Miguel Martínez Carrión, Professor of History and Economic Institutions, University of Murcia, Begoña Candela Martínez, Postdoctoral Researcher in Applied Economics, University of Murcia, Jose Cañabate Cabezuelos, Doctor in History, University of Murcia