Parity May Accelerate the Biological Age Of Post-Menopausal Women

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Our biological age (the rate of biological deterioration and repair) is influenced by various environmental factors and our unique genetic variations. Understanding the factors which accelerate our biological age allows the opportunity for interventions and policies, which will help in maintaining a healthy state within the human body for a longer period of time. The effects of reproduction are theorised to accelerate the biological age of women. This is because reproduction requires a high amount of energy and changes anatomical and physiological systems. Processes such as blood pressure and volume, immune function, hormonal activity, and more are also affected by pregnancy and breastfeeding. Dysregulation of these processes has a major effect on the biological age of a woman. They can lead to conditions such as diabetes, obesity, cardiovascular diseases and more.

Though molecular and demographic measures have linked reproductive costs to an increase in biological aging, studies in regard to parity (the number of times a woman has given birth to a foetus) and biological age using common clinical measures are scarce. Therefore, Shirazi et al conducted a study using cross-sectional epidemiological data, to identify a link between parity and biological age by utilising four composite measures of system integrity and biological age. The measures used were – Homeostatic Dysregulation (HD), the Levine Method Biological Age (LM), the Klemera-Doubal Method Biological Age (KDM) and the allostatic load (AL).

The data was collected from the Centres for Disease Control and Prevention’s National Health and Nutrition Examination Survey in the United States. It detailed information about women from different demographics such as race, education and age and was collected from 1999 to 2010. In this study there were 4418 participants whose data detailed a variety of their reproductive information such as their number of live births, if they were pre-menopausal or post-menopausal and if they had never smoked, has smoked previously or were current smokers. Nine biomarkers (biological measures of the biological state), were used to measure the biological health of women through processes like kidney and liver function.

A U-shaped relationship (non-linear) was mostly shown between parity and an accelerated biological age. The researchers discovered that the biological age of those with less than or more than 3-4 live births had a higher accelerated rate of biological aging than those with 3-4 live births. This was the case when factors such as lifestyle and demographics were controlled. However, the researchers could not determine the physiological processes which caused such heavy costs of reproduction. Using all four composite measures revealed that there is a non-linear relationship  between parity and accelerated biological aging in post-menopausal women (larger similar studies have also shown non-linear relationships- this increases the level of confidence in these results), showing that post-menopausal women are more affected by parity than pre-menopausal women.

A graphical representation of the four composites measures of system integrity and biological age between pre and post menopausal women. A U-shaped relationship can be seen in all measures.
Orange curve: Pre – menopausal women.
Blue curve: Post – menopausal women.
Source: Parity predicts biological age acceleration in post-menopausal, but not pre-menopausal, women. Shirazi et al.

Though the reasons behind the relationship between parity and accelerated biological age is still unclear, the researchers hypothesised the higher mortality with women who give birth to one child may be a result of health problems which hinder them giving birth again. It could also be the mothers experiencing low levels of social support. More research is required into which specific factors cause accelerated biological aging in women who have never given birth and women who have only given birth to one child.

The researchers also suggest that the non-linear relationship between parity and accelerated biological aging may be due to the positive and negative effects of reproduction, in addition to individual risks (such as environmental factors and lifestyle). They also propose that the effects of pregnancy and breastfeeding on systemic processes are long-term and therefore affect women later in life. This may be why accelerated biological aging is seen in post-menopausal women. Additionally, the researchers suggest that post-menopausal women have lower levels of ovarian hormones which contributes to higher morbidity and mortality. More research is required into the mechanisms which halt accelerated biological aging in pre-menopausal women which is stimulated by parity and high reproductive costs.

This study displayed that accelerated biological aging in post-menopausal women may be due to ‘parity and reproductive investment’. Though this study has shown using common clinical measures that there is a relationship between parity and accelerated aging, there were some limitations that were addressed by the researchers such as:

  • This study only included women who had live births, and not those who had miscarriages or aborted pregnancies. These women would also have gone through some of, if not all of the reproductive costs those who had live births had experienced.
  • The data collected is limited to the United States and excludes other western and non-western environments.

I urge you to read the original study which inspired this post (linked below).

Feature Image: GettyImages

Original Source: Shirazi, T.N., Hastings, W.J., Rosinger, A.Y. et al. Parity predicts biological age acceleration in post-menopausal, but not pre-menopausal, women. Sci Rep 10, 20522 (2020). https://doi.org/10.1038/s41598-020-77082-2

Edited by Cyrus Rohani-Shukla

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