MECHANISMS IN ENDOCRINOLOGY: Parity and risk of type 2 diabetes: a systematic review and dose-response meta-analysis

The association between parity and type 2 diabetes mellitus: a cross-sectional, community-based study

BACKGROUND

Limited published data exist on the association between parity (number of deliveries) and diabetes mellitus (DM). This study was conducted to evaluate the association between parity and type 2 DM (T2DM) among Sudanese women.

METHOD

A multistage sampling survey was conducted in four villages in the River Nile State, Sudan, between July and September 2022. The World Health Organization's three-level stepwise questionnaire was adopted to collect women's sociodemographic characteristics (age, sex, height, weight, marital status, parity, education level, occupation, detailed obstetric history, and family history of T2DM). Multivariate analyses were performed.

RESULTS

A total of 397 women were recruited. Their median (interquartile range) age was 45.0 (33.0‒55.7) years. A total of 154 women (38.8%) were nulliparous, whereas 93 (23.4%), 70 (17.6%), and 80 (20.2%) had para 1‒3, 4 or 5, and more than 5, respectively. A total of 112 (28.2%) women had T2DM. In multivariate analysis, older age (adjusted odds ratio, AOR, 1.04, 95%, confidence interval, CI, 1.02‒1.06), high parity (AOR, 1.1, 95% C, 1.01‒1.20), and a family history of DM (AOR, 3.26, 95% CI, 1.98‒5.38) were associated with T2DM. Compared with the nulliparity, para 1‒3 (AOR, 2.33; 95% CI, 1.17‒4.61), para 4 or 5 (AOR, 2.12; 95% CI, 1.04‒4.30), and para > 5 (AOR, 2.16; 95% CI, 1.09‒4.27) were at higher risk of T2DM. In women aged < 50 years, high parity (AOR, 1.22; 95% CI, 1.06‒1.44) was associated with T2DM. Compared with the nulliparous women, para 4 or 5 (AOR, 3.47; 95% CI, 1.16‒10.34) and para > 5 (AOR, 4.63; 95% CI, 1.54‒13.87) were associated with T2DM, whereas para 1‒3 was not associated with T2DM. In the women aged ≥ 50 years, parity and parity groups were not associated with T2DM.

CONCLUSION

There is a high prevalence of T2DM among Sudanese women. Parity and high parity are significant predictors of T2DM among these women in this part of Sudan.

Fraction of cancers attributable to and prevented by reproductive factors and exogenous hormones use in Italy

OBJECTIVE

Endogenous and exogenous hormonal factors have been associated with female breast, genital, and colorectal cancer risk. The aim of the present study is to conduct an evidence-based evaluation of the fraction of cancers attributable to and prevented by exogenous hormonal (i.e., combined oral contraceptives [COC] and combined estrogen-progestogen menopausal therapy [CEPMT]) and reproductive factors (i.e., parity and breastfeeding) in Italy.

STUDY DESIGN

We calculated the population attributable and prevented fractions combining relative risks and prevalence of exposure in Italian women. Italian cancer incidence and mortality data were extracted from national sources and used to estimate the number of cancer cases and deaths attributable to reproductive factors and exogenous hormones in Italy in 2020. For long-term effects, a 20-year latency period was considered.

RESULTS

COC were responsible for 4.4 % of breast and 10.9 % of cervical cancers in women aged 15-44, but also avoided 6.4 % of endometrial, 5.6 % of ovarian, and 2.9 % of colorectal cancers in women of all ages. Overall, COC use prevented 1174 cancer diagnoses and 577 cancer deaths. CEPMT caused 0.4 % of breast cancers at age 45-69. Low parity accounted for 8.1 %, 11.8 % and 15.5 % of breast, endometrial and ovarian cancers, respectively (6267 cases, 1796 deaths). Breastfeeding avoided 6.4 % of breast cancers (3775 cases, 897 deaths).

CONCLUSIONS

Our analysis quantified the complex effects of hormonal and reproductive factors on cancer burden in Italian women.

Reproductive factors, genetic susceptibility and risk of type 2 diabetes: A prospective cohort study

AIM

To explore the relationships of multiple reproductive factors with type 2 diabetes mellitus (T2DM) risk and the joint effects of reproductive factors and genetic susceptibility.

METHODS

We included 262,368 women without prevalent T2DM from the UK biobank. Cox proportional hazards regression models were employed to estimate the relationships of reproductive factors with T2DM risk and the joint effects of reproductive factors and genetic susceptibility.

RESULTS

During a mean follow-up of 12.2 years, 8,996 T2DM cases were identified. Early menarche (<12 years, hazard ratio (HR) 1.08 [95 % confidence interval (CI) 1.02;1.13]), late menarche (≥15 years, HR 1.11 [1.04;1.17]), early menopause (<45 years, HR 1.20 [1.12;1.29]), short reproductive lifespan (<30 years, HR 1.25 [1.16;1.35]), hysterectomy (1.31, HR [1.23;1.40]), oophorectomy (HR 1.28 [1.20;1.36]), high parity (≥4, HR 1.25 [1.17;1.34]), early age at first live birth (<20 years, HR 1.23 [1.16;1.31]), miscarriage (HR 1.13 [1.07;1.19]), stillbirth (HR 1.14 [1.03;1.27]), and ever used hormonal replacement therapy (HR 1.19 [1.14;1.24]) were related to a higher T2DM risk, while ever used oral contraceptives (HR 0.93 [0.89;0.98]) was related to a lower T2DM risk. Furthermore, women with reproductive risk factors and high genetic risk had the highest T2DM risk compared to those with low genetic risk and without reproductive risk factors.

CONCLUSION

Our findings show that multiple reproductive factors are related to T2DM risk, particularly in women with high genetic risk.

Association of Parity With Insulin Resistance Early in Pregnant Women: ECLIPSES Study

CONTEXT

Little is known about whether parity is associated with elevated early-pregnancy insulin resistance (IR), or whether overweight/obesity contributes to increasing the possible effect.

OBJECTIVE

We determined the associations between parity and glucose metabolism parameters in the first trimester of pregnancy in a Mediterranean pregnant population, and whether these associations are affected by overweight/obesity.

METHODS

A cross-sectional study was conducted of 264 healthy pregnant women from the ECLIPSES study who were recruited at 12 weeks of gestation. At baseline, details on socioeconomic status, obstetric history (including parity, ie, number of births), lifestyle factors, anthropometry, and blood samples were collected. Fasting serum glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR) index were assessed in the first trimester. Elevated IR was defined as the upper HOMA-IR tertile (≥1.58). Multivariable linear regression and Cox regression model with constant time were performed.

RESULTS

Parity ranged from 0 to 4. After multivariable adjustment, the insulin levels (β [% change]: 20.92; 95% CI, 4.08-37.71) and HOMA-IR index (β [% change]: 19.72; 95% CI, 2.43-40.49) were positively associated with parity. Additionally, multiparous women, as compared to nulliparous, were more likely to have higher HOMA-IR levels (primiparous [1 birth], β [% change[: 16.88; 95% CI, -1.00 to 37.99; multiparous [≥2 births), β [% change]: 32.18; 95% CI, 3.56-68.71), and an increased relative risk (RR) of an elevated IR (primiparous [1 birth], RR: 1.55; 95% CI, 1.03-2.36; multiparous (≥2 births), RR: 1.72; 95% CI, 1.05-2.83). The combination of multiparity and overweight/obesity conferred a 3.04-fold increase in the RR of elevated IR, which increased proportionally to the number of parities.

CONCLUSION

This study demonstrates that parity may have a negative effect on early-pregnancy IR and that maternal overweight/obesity appears to further aggravate this relationship.

Association between pregnancy-related complications and development of type 2 diabetes and hypertension in women: an umbrella review

BACKGROUND

Despite many systematic reviews and meta-analyses examining the associations of pregnancy complications with risk of type 2 diabetes mellitus (T2DM) and hypertension, previous umbrella reviews have only examined a single pregnancy complication. Here we have synthesised evidence from systematic reviews and meta-analyses on the associations of a wide range of pregnancy-related complications with risk of developing T2DM and hypertension.

METHODS

Medline, Embase and Cochrane Database of Systematic Reviews were searched from inception until 26 September 2022 for systematic reviews and meta-analysis examining the association between pregnancy complications and risk of T2DM and hypertension. Screening of articles, data extraction and quality appraisal (AMSTAR2) were conducted independently by two reviewers using Covidence software. Data were extracted for studies that examined the risk of T2DM and hypertension in pregnant women with the pregnancy complication compared to pregnant women without the pregnancy complication. Summary estimates of each review were presented using tables, forest plots and narrative synthesis and reported following Preferred Reporting Items for Overviews of Reviews (PRIOR) guidelines.

RESULTS

Ten systematic reviews were included. Two pregnancy complications were identified. Gestational diabetes mellitus (GDM): One review showed GDM was associated with a 10-fold higher risk of T2DM at least 1 year after pregnancy (relative risk (RR) 9.51 (95% confidence interval (CI) 7.14 to 12.67) and although the association differed by ethnicity (white: RR 16.28 (95% CI 15.01 to 17.66), non-white: RR 10.38 (95% CI 4.61 to 23.39), mixed: RR 8.31 (95% CI 5.44 to 12.69)), the between subgroups difference were not statistically significant at 5% significance level. Another review showed GDM was associated with higher mean blood pressure at least 3 months postpartum (mean difference in systolic blood pressure: 2.57 (95% CI 1.74 to 3.40) mmHg and mean difference in diastolic blood pressure: 1.89 (95% CI 1.32 to 2.46) mmHg). Hypertensive disorders of pregnancy (HDP): Three reviews showed women with a history of HDP were 3 to 6 times more likely to develop hypertension at least 6 weeks after pregnancy compared to women without HDP (meta-analysis with largest number of studies: odds ratio (OR) 4.33 (3.51 to 5.33)) and one review reported a higher rate of T2DM after HDP (hazard ratio (HR) 2.24 (1.95 to 2.58)) at least a year after pregnancy. One of the three reviews and five other reviews reported women with a history of preeclampsia were 3 to 7 times more likely to develop hypertension at least 6 weeks postpartum (meta-analysis with the largest number of studies: OR 3.90 (3.16 to 4.82) with one of these reviews reporting the association was greatest in women from Asia (Asia: OR 7.54 (95% CI 2.49 to 22.81), Europe: OR 2.19 (95% CI 0.30 to 16.02), North and South America: OR 3.32 (95% CI 1.26 to 8.74)).

CONCLUSIONS

GDM and HDP are associated with a greater risk of developing T2DM and hypertension. Common confounders adjusted for across the included studies in the reviews were maternal age, body mass index (BMI), socioeconomic status, smoking status, pre-pregnancy and current BMI, parity, family history of T2DM or cardiovascular disease, ethnicity, and time of delivery. Further research is needed to evaluate the value of embedding these pregnancy complications as part of assessment for future risk of T2DM and chronic hypertension.

Multiparity increases the risk of diabetes by impairing the proliferative capacity of pancreatic β cells

Pregnancy imposes a substantial metabolic burden on women, but little is known about whether or how multiple pregnancies increase the risk of maternal postpartum diabetes. In this study, we assessed the metabolic impact of multiple pregnancies in humans and in a rodent model. Mice that underwent multiple pregnancies had increased adiposity, but their glucose tolerance was initially improved compared to those of age-matched virgin mice. Later, however, insulin resistance developed over time, but insulin secretory function and compensatory pancreatic β cell proliferation were impaired in multiparous mice. The β cells of multiparous mice exhibited aging features, including telomere shortening and increased expression of Cdkn2a. Single-cell RNA-seq analysis revealed that the β cells of multiparous mice exhibited upregulation of stress-related pathways and downregulation of cellular respiration- and oxidative phosphorylation-related pathways. In humans, women who delivered more than three times were more obese, and their plasma glucose concentrations were elevated compared to women who had delivered three or fewer times, as assessed at 2 months postpartum. The disposition index, which is a measure of the insulin secretory function of β cells, decreased when women with higher parity gained body weight after delivery. Taken together, our findings indicate that multiple pregnancies induce cellular stress and aging features in β cells, which impair their proliferative capacity to compensate for insulin resistance.

Parity and incident type 2 diabetes in older Chinese women: Guangzhou Biobank Cohort Study

This study examined the association between parity and incident type 2 diabetes in older Chinese women and estimated the mediation effect of adiposity indicators. A total of 11,473 women without diabetes at baseline from 2003 to 2008 were followed up until 2012. We used Cox proportional hazards regression to assess the association between parity and incident type 2 diabetes, and mediation analysis to estimate the mediation effect of adiposity indicators. Compared to women with one parity, the hazard ratio (HR) (95% confidence interval (CI)) for incident type 2 diabetes was 0.85 (0.44-1.63), 1.20 (1.11-1.30), 1.28 (1.16-1.41) and 1.27 (1.14-1.42) for women with parity of 0, 2, 3, and ≥ 4, respectively. The proportion of indirect effect (95% CI) mediated by body mass index, waist circumference, hip circumference, waist-to-hip ratio, waist-to-height ratio and body fat percentage was 26.5% (19.2-52.2%), 54.5% (39.4-108.7%), 25.1% (18.2-49.1%), 35.9% (25.6-74.1%), 50.3% (36.5-98.6%) and 15.1% (- 66.4 to 112.3%), respectively. Compared to women with one parity, women with multiparity (≥ 2) had a higher risk of incident type 2 diabetes and up to half of the association was mediated by abdominal obesity.

The association of parity number with multimorbidity and polypharmacy among Iranian women in the Azarcohort: a cross-sectional study

OBJECTIVE

We aimed to study the association of parity number with multimorbidity (MM) and polypharmacy among women in the Azar cohort population.

PATIENTS & METHODS

This cross-sectional investigation was based on data from the Azar Cohort Study. Information regarding demographics, personal habits, physical activity level, medical and reproductive history, and anthropometric measurements of 8,290 females (35-70 years) were evaluated. Ordinal logistic and logistic regression analyses were conducted to assess for associations of parity number with multimorbidity (MM), polypharmacy, chronic disease, and abdominal obesity.

RESULTS

More educated participants and people in the fifth quintile of the Wealth Score Index were less likely to have a higher parity number. With increasing parity numbers, the prevalence of MM, polypharmacy, hypertension, cardiovascular disease, fatty liver disease, stroke, rheumatoid diseases, chronic obstructive pulmonary disease, and cancers tended to rise. Moreover, we found that increasing parity numbers (especially when ≥ 5) enhanced the odds of abdominal obesity, waist-to-hip ratio ≥ 0.85, and waist-to-height ratio ≥ 0.5; these significant associations were more obvious in parity numbers ≥ 9 and WHtR ≥ 0.5.

CONCLUSION

The parity number is associated with MM and polypharmacy in Iranian women enrolled in the Azar Cohort Study. Further studies exploring the pathways (biological, social, and environmental) underlying these relationships will provide clues for preventing morbidity and premature mortality among susceptible andhighly parous women.

Polybrominated diphenyl ethers in type 2 diabetes mellitus cases and controls: Repeated measurements prior to and after diagnosis

BACKGROUND

Previous studies have reported associations between certain persistent organic pollutants (POPs) and type 2 diabetes mellitus (T2DM). Polybrominated diphenyl ethers (PBDEs) are a class of POPs that are found in increasing concentrations in humans. Although obesity is a known risk factor for T2DM and PBDEs are fat-soluble, very few studies have investigated associations between PBDEs and T2DM. No longitudinal studies have assessed associations between repeated measurements of PBDE and T2DM in the same individuals and compared time trends of PBDEs in T2DM cases and controls.

OBJECTIVES

To investigate associations between pre- and post-diagnostic measurements of PBDEs and T2DM and to compare time trends of PBDEs in T2DM cases and controls.

METHODS

Questionnaire data and serum samples from participants in the Tromsø Study were used to conduct a longitudinal nested case-control study among 116 T2DM cases and 139 controls. All included study participants had three pre-diagnostic blood samples (collected before T2DM diagnosis in cases), and up to two post-diagnostic samples after T2DM diagnosis. We used logistic regression models to investigate pre- and post-diagnostic associations between PBDEs and T2DM, and linear mixed-effect models to assess time trends of PBDEs in T2DM cases and controls.

RESULTS

We observed no substantial pre- or post-diagnostic associations between any of the PBDEs and T2DM, except for BDE-154 at one of the post-diagnostic time-points (OR = 1.65, 95% CI: 1.00, 2.71). The overall time trends of PBDE concentrations were similar for cases and controls.

DISCUSSION

The study did not support PBDEs increasing the odds of T2DM, prior to or after T2DM diagnosis. T2DM status did not influence the time trends of PBDE concentrations.

Associations Between Parity and Cognition: Race/Ethnic Differences

BACKGROUND

Race/ethnicity is associated with differences in reproductive history and cognition individually, yet it remains an understudied factor in the relationship between parity and later-life cognition.

OBJECTIVE

To evaluate if the association between parity and cognition differs between racial/ethnic groups.

METHODS

Participants included 778 older, postmenopausal women from the Health and Nutrition Examination Survey (Latina: n = 178, Non-Latino Black [NLB]: n = 169, Non-Latino White [NLW]: n = 431) who self-reported at least one birth. Cognitive outcomes included working memory, learning memory, and verbal fluency. Covariates included age, education, cardiovascular and other reproductive health factors, adult socioeconomic status (SES) and depressive symptoms. We fit a series of linear models to examine a) whether parity was associated with cognitive functioning, b) if this association varied by race/ethnicity through parity by race/ethnicity interactions, and c) individual parity with cognition associations stratified by race/ethnicity.

RESULTS

In the full sample, parity was significantly negatively associated with Digit Symbol Substitution Test (DSST) performance (b = -0.70, p = 0.024) but not Animal Fluency or word-list learning and memory. Tests of race/ethnicity-by-parity interactions were not statistically significant (ps > 0.05). However, stratified analyses by race/ethnicity showed a differential effect of parity on DSST performance, such that parity was significantly negatively associated with DSST performance (b = -1.66, p = 0.007) among Latinas but not in NLWs (b = -0.16, p = 0.74) or NLBs (b = -0.81, p = 0.191).

CONCLUSION

Among Latina, but not NLB or NLW women, greater parity was associated with worse processing speed/executive functioning later in life. Further research is needed to understand the mechanisms driving racial/ethnic differences.

Number of Births and Risk of Diabetes in China's Older Women

As an important life event in individuals' life, childbirth will affect the health of women to different degrees. More and more attention has been paid to whether the number of births will affect the incident diabetes in elderly women, but there are few related studies. Based on the data of the Chinese Longitudinal Healthy Longevity Survey in 2018, 6,159 older women are selected as the study population. Logistic regression analyses are used to estimate the relationship between the number of births and diabetes risk. For each additional birth, the odds ratio of maternal diabetes will decrease by 6.9% and the result is significant at the 1% level, especially among mothers having four children or less. The conclusion is equally applicable in the sample of fathers and urban mothers, but the increase in the number of births will increase the risk of diabetes in rural mothers, although this result is not statistically significant. Later age at first birth, later age at last birth, the longer childbearing period, and birth interval will significantly reduce the risk of diabetes.

Longitudinal changes in concentrations of persistent organic pollutants (1986-2016) and their associations with type 2 diabetes mellitus

BACKGROUND

Positive associations have been reported between persistent organic pollutants (POPs) and type 2 diabetes mellitus (T2DM); however, causality has not been established. Over the last decades, environmental exposure to legacy POPs has decreased, complicating epidemiological studies. In addition, physiological risk factors for T2DM may also influence POP concentrations, contributing to a complex network of factors that could impact associations with T2DM. Longitudinal studies on this topic are lacking, and few have assessed prospective and cross-sectional associations between repeated POP measurements and T2DM in the same individuals, which may shed light on causality.

OBJECTIVES

To compare longitudinal trends in concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in T2DM cases and controls, and to examine prospective and cross-sectional associations between PCBs, OCPs and T2DM at different time-points before and after T2DM diagnosis in cases.

METHODS

We conducted a longitudinal, nested case-control study (1986-2016) of 116 T2DM cases and 139 controls from the Tromsø Study. All participants had three blood samples collected before T2DM diagnosis in cases, and up to two samples thereafter. We used linear mixed-effect models to assess temporal changes of POPs within and between T2DM cases and controls, and logistic regression models to investigate the associations between different POPs and T2DM at different time-points.

RESULTS

PCBs, trans-nonachlor, cis-nonachlor, oxychlordane, cis-heptachlor epoxide, p,p'-DDE, and p,p'-DDT declined more slowly in cases than controls, whereas β-HCH and HCB declined similarly in both groups. Most POPs showed positive associations between both pre- and post-diagnostic concentrations and T2DM, though effect estimates were imprecise. These associations were most consistent for cis-heptachlor epoxide.

DISCUSSION

The observed positive associations between certain POPs and T2DM may be because of higher POP concentrations within prospective T2DM cases, due to slower temporal declines as compared to controls.

Associations between parity, pregnancy loss, and breastfeeding duration and risk of maternal type 2 diabetes: An observational cohort study

BACKGROUND

Parity, pregnancy loss, and breastfeeding duration were found to be associated with diabetes. However, the results are inconsistent. Also, no epidemiological studies have examined the association of these reproductive factors with diabetes in the same large population. We aim to investigate the associations between parity, pregnancy loss, breastfeeding duration, and the risk of maternal diabetes in middle-aged and elderly Chinese females.

METHODS

We included 131 174 females aged ≥40 years from the REACTION study (Risk Evaluation of Cancers in Chinese Diabetic Individuals: A Longitudinal Study). Multivariable linear regression and logistic regression were used to assess the association between parity, pregnancy loss, and breastfeeding duration and type 2 diabetes.

RESULTS

The number of parities and breastfeeding duration were positively related to fasting plasma glucose, 2-hour postload glucose, glycosylated hemoglobin, and homeostatic model assessment of insulin resistance. Compared with those with one birth, nulliparous women or women with 2 or ≥3 births had a significantly increased risk of diabetes. The odds ratios (OR) and 95% confidence intervals (CI) were 1.27 (1.10-1.48), 1.17 (1.12-1.22), and 1.28 (1.21-1.35), respectively. Compared with women without pregnancy loss, those who underwent 2 (OR 1.09; 95% CI, 1.04-1.14) or ≥3 pregnancy losses (OR 1.11; 95% CI, 1.04-1.18) had an increased risk of diabetes. Moreover, women with a breastfeeding duration ≥0 to 6 months (OR 0.82; 95% CI, 0.75-0.90) and ≥6 to 12 months (OR 0.94; 95% CI, 0.89-0.99) had a significantly lower risk of diabetes.

CONCLUSIONS

Nulliparous women or women with multiparity or more than one pregnancy loss have an increased risk of diabetes in later life, while women who breastfeed more than 0 to 12 months have a lower risk of diabetes.

The association of parity/live birth number with incident type 2 diabetes among women: over 15 years of follow-up in The Tehran Lipid and Glucose Study

Background

Childbearing may increase the future risk of developing type 2 diabetes mellitus (T2DM) in mothers. However, the issue is not clear completely and not investigated in the Middle East, a region with a high burden of T2DM. In the current study, we examined the association of parity/live birth number with incident T2DM among Iranian women.

Methods

The study population included 2552 women aged 30–65 years recruited in 1999–2001 and were followed for incident T2DM by 3-year intervals. Multivariable Cox proportional hazard models were applied to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of the parity/live birth number for incident T2DM. Parity number was defined as the number of live childbirth (number of live birth) plus the number of stillbirth (defined as birth of an infant that died after the 20th week of pregnancy in the uterus).

Results

During a median follow-up of 15.4 years, 557 incident T2DM cases have occurred. After adjustment for potential T2DM risk factors and reproductive factors, each additional parity caused a 9% higher risk for incident T2DM. Moreover, compared to women with one parity, those with 3 and ≥ 4 parity had HRs of 1.73 [95% CI: 1.06–2.83] and 2.23 [1.36–3.65], respectively. After further adjustment for body mass index (BMI) and waist circumference, although the HRs were attenuated prominently, parity ≥ 4 was associated with significantly higher risk (HR: 1.72 [1.05–2.83]); even after further adjustment for triglycerides (TG)/ high-density lipoprotein cholesterol (HDL-C), the risk remained marginally significant (HR: 1.64 [1.00–2.70; P value: 0.051]). For the number of live birth, the results were also similar. Moreover, in a sensitivity analysis, when we considered BMI change during follow-up as another covariate, generally, the effect sizes did not change; the trend of HRs across categories of parity number remained marginally significant (P value: 0.064).

Conclusions

During a long-term follow-up, after adjustment for potential T2DM risk factors, reproductive factors, obesity indices, and TG/HDL-C (insulin resistance surrogate), we demonstrated that higher parity/live birth numbers could be associated with increased risk of T2DM development among Iranian women. Moreover, even after further adjustment for BMI change, the suggestive higher risk was still found.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12905-021-01519-7.

Higher Parity Is Associated With Lower Mortality in a European Population of Women With High Fertility: Results From Ireland

Research has often found a U- or J-shaped association between parity and mortality. Many researchers have suggested repeated pregnancy, childbirth, and lactation taxes the body beyond a certain parity level. Available research has concentrated on populations with controlled fertility or historic populations. Ireland presents an opportunity to explore these associations in a modern sample with high fertility. We use data from the Irish Longitudinal Study on Ageing (TILDA) to test whether parity is associated with mortality in women aged 50 years or over (n = 4177). We use Cox proportional hazards models to model survival and adjust for demographics and early life circumstances. We test whether a number of health characteristics mediate these effects. Models were also stratified by birth cohort to test possible cohort effects. Higher parity was associated with lower risk of mortality, even after adjustment for early life and socioeconomic circumstances. This effect was not mediated by current health characteristics. The effects were largely driven by those born between 1931 and 1950. Increasing parity is associated with decreasing mortality risk in this sample. The effects of parity could not be explained through any of the observed health characteristics. These findings are in contrast to much of the literature on this question in similar populations. Lack of fertility control in Ireland may have "selected" healthier women into high parity. Social explanations for these associations should be further explored.

Lactation improves pancreatic β cell mass and function through serotonin production

Pregnancy imposes a substantial metabolic burden on women through weight gain and insulin resistance. Lactation reduces the risk of maternal postpartum diabetes, but the mechanisms underlying this benefit are unknown. Here, we identified long-term beneficial effects of lactation on β cell function, which last for years after the cessation of lactation. We analyzed metabolic phenotypes including β cell characteristics in lactating and non-lactating humans and mice. Lactating and non-lactating women showed comparable glucose tolerance at 2 months after delivery, but after a mean of 3.6 years, glucose tolerance in lactated women had improved compared to non-lactated women. In humans, the disposition index, a measure of insulin secretory function of β cells considering the degree of insulin sensitivity, was higher in lactated women at 3.6 years after delivery. In mice, lactation improved glucose tolerance and increased β cell mass at 3 weeks after delivery. Amelioration of glucose tolerance and insulin secretion were maintained up to 4 months after delivery in lactated mice. During lactation, prolactin induced serotonin production in β cells. Secreted serotonin stimulated β cell proliferation through serotonin receptor 2B in an autocrine and paracrine manner. In addition, intracellular serotonin acted as an antioxidant to mitigate oxidative stress and improved β cell survival. Together, our results suggest that serotonin mediates the long-term beneficial effects of lactation on female metabolic health by increasing β cell proliferation and reducing oxidative stress in β cells.

Gonadal hormonal factors before menopause and incident type 2 diabetes in women: A 22-year follow-up of 83 799 women from the E3N cohort study

BACKGROUND

In many populations the incidence of type 2 diabetes is higher in men than in women. This may be explained by exposure to female gonadal hormones, but so far, there is no consensus on their role over the life course in type 2 diabetes etiology.

METHODS

Data are from 83 799 French women from the E3N (Etude Épidémiologique de Femmes de la Mutuelle Générale de l'Education Nationale) cohort study, followed for 22 years. Multivariable Cox models including classical risk factors were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) between gonadal hormonal factors and incident type 2 diabetes.

RESULTS

Older age at menarche, more menstrual cycles, older age at menopause, longer duration of exposure to gonadal hormones and breastfeeding were inversely associated with incident type 2 diabetes cases (n = 4806). While a longer duration of menstrual cycles (HR = 1.23 [95% CI: 1.07-1.41] comparing ≥32 vs ≤24 days) and use of contraceptive pills (HR = 1.33 [1.25-1.42]) were associated with a greater risk of type 2 diabetes.

CONCLUSIONS

In women, a longer exposure to endogenous gonadal hormones with a later menopause as well as breastfeeding were associated with a lower risk of developing type 2 diabetes, independently of classical diabetes risk factors. In contrast, the use of contraceptive agents was associated with incident diabetes, but the influence of each type of contraception and of exposure duration remain to be investigated.

Costs of reproduction and ageing in the human female

Evolutionary theories of ageing point to reproduction as a significant factor to consider when asking why ageing occurs and why there is inter-individual variation in its progression. Reproduction in human females is costly, in terms of energy, nutrients and metabolic adjustments. Thus, it is expected that women who experienced high reproductive effort resulting from multiple reproductive events will age faster. However, the evidence for long-term negative effects of reproduction is not conclusive. The lack of understanding of whether there are trade-offs between reproduction and ageing in women is partly due to methodological challenges. The costs of reproduction are often calculated based only on parity, while other elements contributing to these costs (e.g. breastfeeding, timing of reproduction) are neglected, which may significantly underestimate the total costs and obscure the all-important inter-individual variation in such costs. Costs must be evaluated in relation to individual characteristics, including developmental conditions, nutritional status and social support that a mother receives during reproduction. Furthermore, ageing and health must be assessed based on comprehensive markers rather than arbitrarily assembled variables. Finally, longitudinal rather than cross-sectional studies and new statistical approaches are needed to reveal how much of a decline in health and progressing ageing can actually be attributed to past reproductive processes. This article is part of the theme issue 'Evolution of the primate ageing process'.

Frailty: A cost incurred by reproduction?

Evolutionary theories of senescence, such as the ‘disposable soma’ theory, propose that natural selection trades late survival for early fecundity. ‘Frailty’, a multidimensional measure of health status, may help to better define the long-term consequences of reproduction. We examined the relationship between parity and later life frailty (as measured by the Frailty Index) in a sample of 3,534 adults aged 65 years and older who participated in the English Longitudinal Study of Ageing. We found that the most parous adults were the most frail and that the parity-frailty relationship was similar for both sexes. Whilst this study provided some evidence for a ‘parity-frailty trade-off’, there was little support for our hypothesis that the physiological costs of childbearing influence later life frailty. Rather, behavioural and social factors associated with rearing many children may have contributed to the development of frailty in both sexes.

Number of Pregnancies and Trajectory of Frailty Index: English Longitudinal Study of Ageing

OBJECTIVES

Women are frailer than men across different populations and age groups. However, the mechanisms are still not fully understood. One possible cause is pregnancy and motherhood. The objective of this study was to examine trajectories of Frailty Index over time according to the number of pregnancies.

DESIGN

A prospective study with repeated measures over 14 years.

SETTING AND PARTICIPANTS

A total of 2060 community-dwelling older women aged ≥60 years in England.

METHODS

The number of pregnancies was calculated as a sum of the number of live births and the number of miscarriages, still-births, or abortions. The Frailty Index (FI) was constructed using 60 deficits and repeatedly calculated every 2 years over 14 years. Trajectories of FI according to the number of pregnancies were estimated by a mixed effects model.

RESULTS

Mean FI was 0.15 at baseline. A mixed effects model adjusted for age, smoking, alcohol use, education, and wealth showed that FI increased over time. A higher number of pregnancies were significantly associated with a higher FI (estimate = 0.0047, 95% confidence interval = 0.0020, 0.0074).

CONCLUSIONS AND IMPLICATIONS

The current study showed that a higher number of pregnancies were significantly associated with a higher degree of frailty at baseline and over time. Pregnancy and child rearing may explain some of the observed excess risk of frailty in women. Pregnancy-related factors, such as pregnancy loss, types of delivery, length of pregnancy, childbearing, and child rearing, should be examined in relation to frailty in future studies.

Pregnancy, postpartum and parity: Resilience and vulnerability in brain health and disease

Risk and resilience in brain health and disease can be influenced by a variety of factors. While there is a growing appreciation to consider sex as one of these factors, far less attention has been paid to sex-specific variables that may differentially impact females such as pregnancy and reproductive history. In this review, we focus on nervous system disorders which show a female bias and for which there is data from basic research and clinical studies pointing to modification in disease risk and progression during pregnancy, postpartum and/or as a result of parity: multiple sclerosis (MS), depression, stroke, and Alzheimer's disease (AD). In doing so, we join others (Shors, 2016; Galea et al., 2018a) in aiming to illustrate the importance of looking beyond sex in neuroscience research.

Parity and risk of maternal cardiovascular disease: A dose-response meta-analysis of cohort studies

BACKGROUND

Parity has been reported to play an important role in the development of cardiovascular disease; however, the results are still controversial. We aimed to conduct a meta-analysis of cohort studies to assess quantitatively the association between parity and cardiovascular disease risk.

METHODS

PubMed and Web of Science databases were searched to 1 June 2018, supplemented by manual searches of the bibliographies of retrieved articles. And multivariate-adjusted relative risks were pooled by using random-effects models. Restricted cubic spline analysis with four knots was used to explore the relationship of parity and the risk of cardiovascular disease.

RESULTS

Ten cohort studies involving 150,512 incident cases of cardiovascular disease among 3,089,929 participants were included in the meta-analysis. A significant association between parity and cardiovascular disease risk was observed while comparing parity with nulliparity, with a summarised relative risk of 1.14 (95% confidence interval (CI) 1.09-1.18; I² = 62.0%, P = 0.002). In the dose-response analysis, we observed a potential non-linear J-shaped dose-response relationship between the number of parity and cardiovascular disease risk, the summary risk estimates for an increase of one live birth was 1.04 (95% CI 1.02-1.05), with significant heterogeneity ( I² = 89.6%). In addition, the similar J-shaped associations between parturition number and cardiovascular disease, ischaemic heart disease or stroke risk were also observed.

CONCLUSIONS

Our findings suggest that ever parity is related to cardiovascular disease risk and there is an association between the number of pregnancies and the risk of cardiovascular disease. Since the number of included studies was limited, further studies are warranted to confirm our findings.

Diabetes among Māori women with self-reported past gestational diabetes mellitus in a New Zealand Māori community

BACKGROUND

Gestational diabetes mellitus (GDM) is a risk factor for subsequent development of type 2 diabetes mellitus (T2DM). We have investigated the extent of this risk among Māori women without known diabetes.

MATERIALS AND METHODS

We recruited 2786 Māori women aged 28-86 years between 2004 and 2006, without diagnosed diabetes from the Waikato and Southern Lakes regions, via media, community and general practitioner channels, and invited them for an oral glucose tolerance test (OGTT).

RESULTS

Fifty (1.8%) women reported previous GDM (pGDM). The prevalence decreased significantly with age (P = 0.009). Women aged <50 years with pGDM had higher body mass index (35.6 ± 6.7 vs 32.4 ± 7.7 kg/m2 , P < 0.01), waist circumference (105.3 ± 18.8 vs 96.9 ± 16.6 cm, P < 0.01), fasting blood glucose (5.5 ± 1.0 vs 5.1 ± 0.8 mmol/L, P ≤ 0.01), two-hour post-prandial blood glucose (6.6 ± 3.0 vs 5.6 ± 2.1 mmol/L, P < 0.01) and HbA1c (6.0 ± 0.8 vs 5.8 ± 0.6%, P < 0.05) than women without pGDM. PGDM was a significant risk factor for undiagnosed diabetes (odds ratio 4.0; (5% confidence interval 1.67-9.71). Undiagnosed diabetes was significantly more prevalent among women with than without pGDM aged <40 years (20.0% vs 1.5%).

CONCLUSION

Self-reported past GDM was a significant risk factor for undiagnosed diabetes in this Māori population, particularly among women aged <40 years, highlighting the importance of targeting this group for more intensive screening.

Effect of multiparity and ethnicity on the risk of development of diabetes: a large population-based cohort study

AIMS

To investigate the relationship between increasing parity and diabetes in a large, population-based cohort, and to examine if this relationship is different among high-risk ethnic groups.

METHODS

A population-based, retrospective cohort study was performed in 738 440 women aged 18-50 years, who delivered babies in Ontario between 1 April 2002 and 31 March 2011. Diabetes incidence postpartum was calculated for each parity and ethnic group. A multivariable analysis of the effect of parity and ethnicity on the incidence of diabetes was performed using a Cox proportional hazards model, adjusting for confounders.

RESULTS

The diabetes incidence rate per 1000 person-years was 3.69 in women with 1 delivery, 4.12 in women with 3 deliveries and 7.62 in women with ≥5 deliveries. Women with ≥3 deliveries had a higher risk of developing diabetes compared with women with 1 delivery [adjusted hazard ratios 1.06 (95% CI 1.01-1.11) for 3 deliveries, 1.33 (95% CI 1.25-1.43) for 4 deliveries and 1.53 (95% CI 1.41-1.66) for ≥5 deliveries). A similar rise in risk could be seen in Chinese and South-Asian women, with the most influence in Chinese women [hazard ratio 4.59 (95% CI 2.36-8.92) for ≥5 deliveries].

CONCLUSIONS

There was a positive and graded relationship between increasing parity and risk of development of diabetes. The influence of parity was seen in all ethnicities. This association may be partly related to increasing weight gain and retention with increasing parity, or deterioration in β-cell function. This merits further exploration.

Central fat accretion and insulin sensitivity: differential relationships in parous and nulliparous women

BACKGROUND/OBJECTIVES

Childbearing is associated with a disproportionate accumulation of visceral fat and an increased risk of metabolic disease. However, it is unknown whether the visceral fat accretion associated with pregnancy modifies a woman's risk for metabolic disease. The purpose of this study was to test whether the association between abdominal fat and insulin sensitivity differs by parity status in healthy overweight women.

SUBJECTS/METHODS

Intra-abdominal adipose tissue (IAAT) via CT, body composition by DXA, insulin sensitivity via intravenous glucose tolerance test and minimal model (SI), HOMA-IR, and cardiorespiratory fitness (VO2max) were assessed in 212 non-diabetic, premenopausal, overweight non-Hispanic white and African-American women.

RESULTS

Nulliparous women (n=98) were younger, had less IAAT and higher VO2max, but similar SI, HOMA-IR and leg fat, compared to parous (n=114). In nulliparous women, IAAT was negatively associated with SI, controlling for age, race and body fat mass (r=-0.40, P<0.001), but this relationship was attenuated in parous women (r=-0.15, P=0.16). In multiple linear regression analysis, leg fat and IAAT were significant predictors of SI in nulliparous, but not parous women.

CONCLUSIONS

Results suggest that greater IAAT in parous women does not lead to greater insulin resistance; rather, transient insulin resistance during pregnancy may encourage intra-abdominal fat accumulation that is metabolically benign. This underscores the need to consider parity when assessing cardiometabolic risk.

Number of parity and the risk of rheumatoid arthritis in women: A dose-response meta-analysis of observational studies

AIM

The association between parity and rheumatoid arthritis (RA) risk has been investigated, but results are controversial. Thus, our aim was to systematically analyze the effect of number of parity on the risk of RA in women.

METHODS

Relevant published studies were identified using PubMed and embase databases through 1 April 2016. We pooled the relative risks (RR) and 95% confidence intervals (CI) using random-effects models.

RESULTS

In all, 12 studies with a total of 2 497 580 participants and 11 521 RA cases were included. A borderline significant inverse association was observed when we compared parity with nulliparity for RA, with summarized RR = 0.90 (95%CI: 0.79-1.02; I²  = 58.5%, P_{heterogeneity}  = 0.010). In dose-response analysis, we observed a significant nonlinear (P_nonlinearity  = 0.000) relation between parity number and the risk of RA. Compared with null parity, the pooled RR of RA were 0.89 (95%CI: 0.86-0.93), 0.84 (95%CI: 0.79-0.89), 0.85 (95%CI: 0.79-0.90), 0.88 (95%CI: 0.81-0.95), 0.90 (95%CI: 0.83-0.97), 0.92 (95%CI: 0.84-1.02), and 0.94 (95%CI: 0.83-1.07) for 1, 2, 3, 4, 5, 6, and 7 live births, respectively. Subgroup and sensitivity analyses showed similar associations. No publication bias was found.

CONCLUSION

The findings from the current meta-analysis indicate that parity was related to decreased risk of RA. The greatest risk reduction appeared when the parity number reached two. Further studies are warranted to confirm our findings.