according to the two latest who assessments , cataract has consistently been the leading cause of world blindness , which was responsible for around 48% and 51% of blindness in 2002   and 2010 , respectively .
biological ageing plays the most crucial role in the development of cataract [ 35 ] .
china , the most populous country , has been experiencing an unprecedented ageing due to a lower birth rate   and longer life expectancy .
about 15.5% of the entire chinese were aged 60 + years in 2014 , a figure much higher than the threshold for ageing society ( 10% ) .
therefore as an age - related disease , cataract requires increased and urgent attention in china [ 8 , 9 ] . besides age ,
many other related factors , such as diabetes and gender , have also been well - addressed in previous studies [ 1013 ] .
it has been demonstrated that diabetics faced 25 times greater risk of developing cataracts than the nondiabetic counterparts .
additionally , gender diversity in the prevalence of cataract has also been frequently reported and most studies showed greater prevalence among females than males .
hormonal differences between men and women may mainly contribute to such gender diversity [ 10 , 14 ] , but the reasons were still not fully understood .
ocular changes may arise during pregnancy due to the modifications of hormone , metabolism , and weight .
although most of the changes are reversible , some are occasionally permanent which may in turn cumulatively affect women 's vision at their older ages .
a study revealed that there was a significant association between parity and the risk of cataract among middle- and older age women .
however , the evidence is scant since very few studies have directly reported the link between childbearing and cataract , especially for women in their old ages . in this study , we aim to ( 1 ) test the relationship between childbearing and cataract among the older women and ( 2 ) examine whether diabetes is a mediator in this relationship .
as previously described , we conducted a large scale cross - sectional survey among 14,292 older adults aged 60 + years in xiamen , china , in 2013 .
all 38 subdistricts in xiamen were selected . in stage 2 , one - third of communities
were randomly sampled from each subdistrict and a total of 173 communities were included in the end .
the randomization of these communities was performed by computer - generated random numbers . in stage 3 , participants were conveniently selected from each community by controlling for gender and age composition .
the number of individuals to be sampled in each community was determined according to its proportion of eligible older adults .
participants ' demographic characteristics , activities of daily living , physical health , psychological health , and social support were assessed by a structural questionnaire , which was finished by a face - to - face interview . written informed consent was obtained by each participant and our study was approved by the ethical review committee of school of public health , xiamen university .
the primary outcomes in this study were whether the participants suffered from physician - diagnosed cataract and diabetes .
they were assessed by the same item :  do you suffer from the following physician - diagnosed chronic diseases ? ( check all that apply ) . 
only if the option was ticked , we assume the participant suffered from the corresponding chronic disease . in xiamen
, for medical screening purposes , people who were aged 60 years or older can participate in an annual physical examination for free in recent years , including blood pressure and blood glucose checks , and an ocular examination .
moreover , some self - reported chronic diseases were reported to be highly correlated with physician 's records .
therefore , the reliability of self - reported diabetes and cataract in the elderly should be potentially ensured ( see supplementary 1 for the reason in detail in supplementary material available online at http://dx.doi.org/10.1155/2015/385815 ) .
the nondiabetic cataracts in our study referred to the individuals who suffered from cataract but did not have diabetes .
the exposure of interest was childbearing status which was measured by number of children ( noc ) .
 numerical response was obtained and was classified into six levels : 0 , 1 , 2 , 3 , 4 - 5 , and 6 or more .
additionally , some basic information ( gender , age , residence , education , and marital status ) , life habits ( dietary salt intake , smoking history , and alcohol drinking ) , and hypertension status were included as covariates ( see table 1 for the details of the classification of the variables ) .
we considered the hypertension status as a covariate because it has also been frequently reported to have relationship to cataract .
first , we summarized the characteristics of participants by cataract status using descriptive statistics ( mean and standard deviation for age and counts and proportions for the other categorical characteristics ) .
chi - square tests were performed to assess the relationship between cataract and all the other covariates .
second , to identify the relationships among noc , diabetes , and cataract in women , stata v 13.0 was used to perform structural equation modeling ( sem ) .
the reason we tested their relationships was due to the concern that diabetes may be a mediator in the relationship between noc and cataract .
the sem for this mediation model for the ith participant ( 1  i  n ) is given by(1)logitprobabilitydi=0+1noci+i , logitprobabilityci=0+1di+2noci+3tcovariates+i , where the outcome di is diabetic status , ci is cataract status , 0 , 1 , 0 , 1 , 2 , and 3 are the regression coefficients , covariates are the nine covariates described above , and i and i are the random errors .
third , we presented the prevalence of cataract by line chart under the six levels of noc , stratified by gender and diabetes status .
fourth , logistic regressions were carried out to model the cataract status on the noc among the participants without diabetes , stratified by gender and adjusted by the nine covariates mentioned above . p
among the 14,292 participants , 14,119 had complete data on all variables mentioned above and were included in the following analyses .
descriptive statistics of characteristics stratified by gender and cataract status were presented in table 1 . among 14,119 valid participants , the prevalence of cataract was 5.01% , with an obviously higher prevalence in women than men ( 6.41% versus 3.51% ) .
the average age was significantly higher in cataract participants than in those without cataract for both men and women ( p < 0.001 ) .
an increase trend of prevalence of cataract was presented as noc grew for women and ranged from 3.10% for the childless to 9.09% for those who had six or more children .
about ten percent of participants suffered from diabetes , of whom the prevalence values of cataract were 4.48% for men and 9.26% for women , which were both higher than their nondiabetic counterparts .
approximately thirty percent of participants reported to have hypertension and 6.85% of them reported to have cataract .
significantly higher prevalence of cataract was presented in hypertensive participants than nonhypertensive groups for both men and women .
female participants who had salt - heavy diet , were illiterate , were single or widowed , and had quit drinking had significantly higher prevalence of cataract ( p < 0.05 ) .
however , for male participants , except for the hypertensive status , only smoking history was significantly associated with cataract status .
unexpectedly , men who had quit smoking presented highest prevalence , and those who smoked often showed lowest one . as descriptive results shown above , both diabetes and having more children increase the risk of cataract for older women . to test whether diabetes is a mediator in the relationship between noc and cataract , mediation analysis with sem was performed .  
figure 1 presented the path diagram with estimated odds ratios ( or ) , which represented the sem models for female elderly ( equation ( 1 ) ) .
diabetic women had a statistically higher risk ( or = 1.33 ) of cataract than their nondiabetic counterparts .
those who had one or more children faced roughly 24 times higher risk of cataract than the childless women .
however , all the paths between noc and diabetes were not significant , indicating that diabetes should not be a mediator in the relationship between noc and cataract .
the details of the estimates of the sem models can be found in supplementary 2 .
the prevalence of cataract under the six levels of noc stratified by gender and diabetic status was depicted by line chart in figure 2 .
a notably increased prevalence ( solid line ) appeared as noc grew for nondiabetic older women , but it disappeared among the nondiabetic older men ( dotted line ) .
moreover , the nondiabetic females had higher prevalence of cataract than nondiabetic males at all levels of noc except among the childless participants .
at all the levels of noc , diabetic females had obvious higher prevalence of cataract than diabetic males .
the increased trend of prevalence as having more children disappeared for diabetic female and male participants . 

table 2 presented the ors with corresponding 95% confidence intervals ( cis ) obtained from logistic regression models for nondiabetic participants stratified by gender .
for both nondiabetic women and men , age was a crucial risk factor for developing cataract .
the older women who had one or more children faced roughly 24 times higher risk of nondiabetic cataract than their childless counterparts ( or [ 95% ci ] = 3.88 [ 1.24 , 17.71 ] , 3.21 [ 1.04 , 14.52 ] , 4.32 [ 1.42 , 19.44 ] , 4.41 [ 1.46 , 19.74 ] , and 3.98 [ 1.28 , 18.10 ] for having 1 , 2 , 3 , 4 - 5 , and 6 or more children , resp . ) .
however , among the nondiabetic older men , the ors seemed to decrease as noc grew , although they were not statistically significant .
hypertension , salt - heavy diet , and living in a city were risk factors for women but not for men .
unexpectedly , having quit smoking was a risk factor , and being widowed was a protect factor for men only .
the findings in this study indicated that childbearing may increase the risk of nondiabetic cataract in women 's old age .
after controlling for the potential confounders , nondiabetic women who had one or more children faced roughly 24 times higher risk of cataract than the childless .
moreover , sem analysis suggested that diabetes was not a mediator in the relationship between noc and cataracts .
these results may contribute to the existing body of literature on identifying the risk factor of cataract among the older individuals .
however , some possible explanations for the childbearing effect in older women may be speculated ; these include ( 1 ) pregnancy - induced estrogen changes .
some investigators believed that estrogen played a protective role in controlling the development of cataract .
a previous study indicated that the risk of cortical cataract increased by about 5% for each one year increment in age at menarche and that the risk decreased by 11% for each five years of age
therefore , we may postulate that the increased risk of cataract for women having more children is due to a reduction in lifetime exposure to circulating estrogens induced by each pregnancy and breastfeeding .
( 2 ) postpartum obesity may be another important risk factor of cataract for women in their later life [ 23 , 24 ] .
a previous study presented that the average gestational weight gains for chinese women ( 17.3  4.9  kg , 17.4  4.4  kg , and 15.7  5.1  kg for women of low , moderate , and high prepregnancy body mass index , resp . )   were much higher than the recommended criteria   ( 1316.7  kg , 1116.4  kg , and 7.114.4  kg , resp . ) .
( 3 ) various ocular changes occur during pregnancy , including decreased sensitivity of the cornea , enlarged blind spots , and bitemporal loss [ 27 , 28 ]
. the cumulative effect of those asymptomatic and subtle ocular changes may also contribute to the development of cataract for women in later life .
( 4 ) a complex of other risk factors , such as the stress for taking care of many children , may also increase the risk of cataract .
however , in either case , more physiological studies were in great need to fully elucidate the mechanism . in line with many previous studies [ 2931 ] ,
cataract was more common in women than men , with the prevalence of 6.41% versus 3.51% in the present study .
such difference is often addressed by the estrogen deficiency   or biomass cooking fuels . however
the prevalence of cataract among childless women was notably lower than that among childless men ( 3.1% versus 5.1% ) .
this result may further indicate that childbearing was an important risk factor of cataract among older women .
a study has directly stated that the risk of cataract in young women ( 3545 years ) increased by an estimated 20% for each additional birth . moreover ,
older women ( 4586 years ) were observed to have 11.3% higher risk of cataract for each additional live birth in a recent cohort study . among the nondiabetic women , the prevalence of cataract grew as they had more children , but such trend disappeared among the women with diabetes . in other words , the effect of childbearing on cataract among the female older adults
cataract was the second most ocular common complication of diabetes , and the effect of diabetes on cataract should be direct and obvious .
however , the childbearing occurred at women 's younger age and its effect on age - related cataract may be cumulative and subtle . therefore the effect of childbearing on cataract is easy to be neglected or covered by other stronger risk factors .
consistent with many previous studies [ 3537 ] , our findings identified hypertension , salt - heavy diet , living in a city , and having quit smoking as risk factors for development of cataract .
salt - heavy diet has been well - addressed to be related to hypertension [ 38 , 39 ] , which may increase the risk of development of the posterior subcapsular cataracts [ 40 , 41 ] . as for smoking , it had been consistently stated to be associated with both nuclear and posterior subcapsular cataract . in this study , having quit smoking was a risk factor for older men which might be due to the smoking history in their younger age .
some investigators found that risk of cataract remains elevated for many years following smoking cessation .
unexpectedly , we found men who smoked often had obviously lower prevalence of cataract than those who never smoked ( 2.81% versus 3.61% ) .
, we further analyzed our data and found that individuals who smoked often were significantly younger than those who never smoked ( 69.45 years versus 71.78 years , p < 0.01 ) , especially among men ( 69.12 years versus 71.77 years , p < 0.01 ) .
therefore , age , the most critical risk factor of cataract , probably confounded the relationship between cataract and smoking history .
this speculation was further validated in the following regression model for men where or for smoking often was higher than never smoking ( 1.07 versus 1.00 ) , after controlling for age and other impact factors .
another possible explanation is that some related chronic diseases can prompt smoking cessation for older adults , and the current smokers may have or believe they have relatively better physician conditions .
however , this speculation can not be validated in this study due to our cross - sectional survey and limited measurements . to fully uncover the relationship between smoking and cataract , variables such as smoking pack - years , age of smoking cessation , and the reason(s ) for smoking cessation are in great need .
despite the fact that abovementioned risk factors of cataracts were well - demonstrated , limited studies have elucidated the gender - specified risk factors .
our results suggested that salt - heavy diet and hypertension were the risk factors for nondiabetic female only and on the contrary , having quit smoking was for nondiabetic male only .
the findings in the present study have uncovered the relationship between childbearing and cataract in older adults .
they may open new research challenges to detect the risk factors of senile cataract . nevertheless , some limitations should be acknowledged .
first , the chronic conditions were obtained by a self - reported question . as a result
, substantial agreement was found in a study comparing subjects ' self - reported diabetes with information from medical records .
some studies demonstrated that self - reported diabetes was > 92% reliable over time   and it was a reliable proxy for medical record review .
the difference between self - reporting and true prevalence of cataract has been evaluated in supplementary 1 , and the reliability of self - reported cataract in this study may also be potentially ensured .
second , to exclude the diabetes - induced cataracts , the data of the participants with diabetes were all removed from our regression models . however , some of participants may have cataract prior to diabetes or the cataracts were not diabetes - induced , and as a result , the complete exclusion may consequently result in some bias .
nevertheless , such bias was restricted , since only 71 ( less than 1% ) female participants had both cataract and diabetes .
third , there are three primary types of age - related cataracts ( nuclear , cortical , and posterior subcapsular ) , and each may have its own somewhat varying causes [ 37 , 41 ] .
however , the types of cataracts were not asked in our survey and therefore we can not specify which type(s ) of cataract were accounted for in relation to childbearing .
this study has revealed a relationship between childbearing status and the risk of cataract among chinese elderly , and diabetes was not a mediator in this relationship . as a result
, we should pay more attention to the eyes care for the women during pregnancy and after childbirth .
 
 backgrounds . 
 ocular changes may arise during pregnancy and after childbirth , but very few studies have reported the association between childbearing and cataract among older adults . methods . 
 14,292 individuals aged 60 + years were recruited in xiamen , china , in 2013 . 
 physician - diagnosed cataract and diabetes status were assessed by a self - reported questionnaire . 
 childbearing status was measured by number of children ( noc ) . 
 structural equation modeling ( sem ) analysis was conducted to examine the relationships among noc , diabetes , and cataract . 
 gender - specific logistic models regressing nondiabetic cataract on noc were performed by adjusting some covariates . 
 results . 
 14,119 participants had complete data , of whom 5.01% suffered from cataract , with higher prevalence in women than men ( 6.41% versus 3.51% ) . 
 estimates of sem models for women suggested that both noc and diabetes were risk factors for cataract and that no correlation existed between noc and diabetes . 
 women who had one or more children faced roughly 24 times higher risk of nondiabetic cataract than their childless counterparts ( or [ 95% ci ] = 3.88 [ 1.24 , 17.71 ] , 3.21 [ 1.04 , 14.52 ] , 4.32 [ 1.42 , 19.44 ] , 4.41 [ 1.46 , 19.74 ] , and 3.98 [ 1.28 , 18.10 ] for having 1 , 2 , 3 , 4 - 5 , and 6 or more children , resp . ) . 
 conclusions . 
 childbearing may increase the risk of nondiabetic cataract in chinese women 's older age . 
1. Introduction
2. Methods
3. Results
4. Discussion
5. Conclusions