Age at menarche and lung function: a Mendelian randomization study
Age at menarche and lung function: a Mendelian randomization study
Dipender Gill 0 1 2 3 4 5 6 8 10 11 13 14 15
Nuala A. Sheehan 0 1 2 3 4 5 6 8 10 11 13 14 15
Matthias Wielscher 0 1 2 3 4 5 6 8 10 11 13 14 15
Nick Shrine 0 1 2 3 4 5 6 8 10 11 13 14 15
Andre F. S. Amaral 0 1 2 3 4 5 6 8 10 11 13 14 15
John R. Thompson 0 1 2 3 4 5 6 8 10 11 13 14 15
Raquel Granell 0 1 2 3 4 5 6 8 10 11 13 14 15
Be´ne´dicte Leynaert 0 1 2 3 4 5 6 8 10 11 13 14 15
Francisco Go´ mez Real 0 1 2 3 4 5 6 8 10 11 13 14 15
Ian P. Hall 0 1 2 3 4 5 6 8 10 11 13 14 15
Martin D. Tobin 0 1 2 3 4 5 6 8 10 11 13 14 15
Juha Auvinen 0 1 2 3 4 5 6 8 10 11 12 13 14 15
Susan M. Ring 0 1 2 3 4 5 6 8 10 11 13 14 15
Marjo-Riitta Jarvelin 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15
Louise V. Wain 0 1 2 3 4 5 6 8 10 11 13 14 15
John Henderson 0 1 2 3 4 5 6 8 10 11 13 14 15
Deborah Jarvis 0 1 2 3 4 5 6 8 10 11 13 14 15
Cosetta Minelli 0 1 2 3 4 5 6 8 10 11 13 14 15
0 St. Mary's Hospital, Imperial College Healthcare NHS Trust , London , UK
1 Division of Respiratory Medicine, Queen's Medical Centre, University of Nottingham , Nottingham , UK
2 Department of Clinical Pharmacology and Therapeutics, Imperial College London, Hammersmith Hospital , London , UK
3 Department of Clinical Science, University of Bergen , Bergen , Norway
4 Unit of Primary Care, Oulu University Hospital , Oulu , Finland
5 National Institute for Health Research, Leicester Respiratory Biomedical Research Unit, Glenfield Hospital , Leicester , UK
6 Department of Gynecology and Obstetrics, Haukeland University Hospital , Bergen , Norway
7 Biocenter Oulu, University of Oulu , Oulu , Finland
8 UMR 1152, Pathophysiology and Epidemiology of Respiratory Diseases, Epidemiology Team, Inserm , Paris , France
9 Center for Life Course Epidemiology, Faculty of Medicine, University of Oulu , Oulu , Finland
10 School of Social and Community Medicine, University of Bristol , Bristol , UK
11 MRC-PHE Centre for Environment and Health , London , UK
12 Institute of Health Sciences, University of Oulu , Oulu , Finland
13 Population Health and Occupational Disease, NHLI, Imperial College London , Emmanuel Kaye Building, 1B Manresa Road, SW3 6LR London , UK
14 Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London , London , UK
15 Department of Health Sciences, University of Leicester , Leicester , UK
A trend towards earlier menarche in women has been associated with childhood factors (e.g. obesity) and hypothesised environmental exposures (e.g. endocrine disruptors present in household products). Observational evidence has shown detrimental effects of early menarche on various health outcomes including adult lung function, but these might represent spurious associations due to confounding. To address this we used Mendelian randomization where genetic variants are used as proxies for age at menarche, since genetic associations are not affected by classical confounding. We estimated the effects of age at menarche on forced vital capacity (FVC), a proxy for restrictive lung impairment, and ratio of forced expiratory volume in one second to FVC (FEV1/FVC), a measure of airway obstruction, in both adulthood and adolescence. We derived SNP-age at menarche association estimates for 122 variants from a published genome-wide meta-analysis (N = 182,416), with SNP-lung function estimates obtained by meta-analysing three studies of adult women (N = 46,944) and two of adolescent girls (N = 3025). We investigated the impact of departures from the assumption of no pleiotropy through sensitivity analyses. In adult women, in line with previous evidence, we found an effect
UMR 1152, Univ Paris Diderot - Paris 7, Paris, France
on restrictive lung impairment with a 24.8 mL increase in
FVC per year increase in age at menarche (95% CI
1.8–47.9; p = 0.035); evidence was stronger after
excluding potential pleiotropic variants (43.6 mL; 17.2–69.9;
p = 0.001). In adolescent girls we found an opposite effect
(-56.5 mL; -108.3 to -4.7; p = 0.033), suggesting that
the detrimental effect in adulthood may be preceded by a
short-term post-pubertal benefit. Our secondary analyses
showing results in the same direction in men and boys, in
whom age at menarche SNPs have also shown association
with sexual development, suggest a role for pubertal timing
in general rather than menarche specifically. We found no
effect on airway obstruction (FEV1/FVC).
The timing of sexual development in women has shown a
secular trend with a shift towards an earlier age over the
years , and this has been related to childhood life-style
and social factors, including diet and obesity,
psychological stress and deprivation, as well as environmental
exposures, including endocrine disruptors found in many
household products . Menarche, defined as the date of
the first day of the first menstrual bleeding, is preceded by a
complex hormonal cascade and signals the initiation of the
menstrual cycle in adolescent girls. Earlier age at menarche
has been described as a risk factor for a number of adverse
health outcomes, including obesity , type 2 diabetes ,
cardio-metabolic traits , cardiovascular morbidity and
mortality , as well as breast  and ovarian  cancers.
Understanding the effects of the age at menarche offers
insight into the pathophysiology of related diseases. In
particular this can highlight the potential effects of early
and late exposure to sex hormones on health outcomes in
women, as well as help explain gender differences in the
risks of common diseases [9–11].
Timing of menarche has been considered an important
factor in relation to respiratory health . Lung function
is an important predictor of both respiratory disease and
overall health. After cessation of lung growth by the early
twenties, there is a plateau in lung function followed by
gradual age-related decline. There are two common
patterns of lung function impairment, obstruction and
restriction, and these have a different impact on morbidity
and mortality . Obstruction, measured as a low ratio of
the forced expiratory volume in one second (FEV1) to the
forced vital capacity (FVC), represents an objective marker
of chronic obstructive pulmonary disease, a major and
growing cause of morbidity, disability and death
worldwide. Restriction, defined as low total lung capacity
(measured by plethysmography) but commonly
approximated by low FVC in population-based studies, is a
predictor of all-cause mortality even in the absence of chronic
respiratory conditions. There has been increasing interest in
understanding gender-related risk factors for lung function
impairment, particularly in relation to hormonal influences
and sexual development. Substantial evidence shows that
lung function is influenced by sex hormones in women 
for whom low lung function has been associated with
irregular menstruation, menopausal transition, and both
natural and surgical menopause, with report of
improvement in lung function in postmenopausal women receiving
hormone replacement therapy [12, 15].
An observational study of 2873 women aged
27–57 years investigated the association of early menarche
with adult lung function and found a lower FVC and FEV1,
but not FEV1/FVC, in women with early menarche .
This work took account of important potential confounders,
including age, height, body mass index (BMI), smoking,
education and birth order, as well as secular trends (age at
menarche has changed over the years and lung function has
also changed due to changes in height). However, the effect
of residual confounding by unmeasured, or poorly recalled,
early life and childhood factors cannot be ruled out. For
example, age at menarche is influenced by childhood
nutritional status , which in turn might influence lung
function in adult life; another example is birth weight,
which has been associated with both age at menarche 
and lung function . Such limitation is typical of
observational studies, where confounding can make it hard
to distinguish between causal effects and spurious
Mendelian randomization (MR) can help assess the
causality of an observed association by using genetic
variants as proxies, or ‘‘instrumental variables’’, for the
exposure of interest [20, 21]. Genetic associations are not
typically affected by confounding or reverse causation
because genes are randomly allocated at the time of
conception. Provided the underlying assumptions are satisfied
, the demonstration that genetic variants known to
modify age at menarche also modify lung function
provides indirect evidence of a causal effect of age at
menarche. The MR technique has been rapidly growing in
popularity because of these advantages over the classical
epidemiological approach, with MR studies having
previously investigated age at menarche as a risk factor for
depression , and lung function as an outcome in
relation to C-reactive protein .
In this study we used MR to investigate the lifetime
effect of age at menarche on lung function in adolescent
girls and adult women, using 122 single nucleotide
polymorphisms (SNPs) associated with age at menarche. We
considered the effects in both adulthood and adolescence,
since we hypothesised that they could differ due to a
different role of menarche in lung growth, maximal lung
function attained, and lung function decline.
SNP-age at menarche association estimates
We derived SNP-age at menarche association estimates
from a published genome-wide association (GWA)
metaanalysis of 57 studies on 182,416 women of European
descent, which identified 122 independent SNPs at 106
genomic loci (p value \ 5 9 10-8) . Overall, the 122
SNPs explained 2.7% of the variability of age at menarche
in the population. Age at menarche was based on
selfreporting and analysed as a continuous variable, with
study-specific analyses adjusted for birth year, to account
for the secular trends in menarche timing, and genomic
control, to account for population stratification . We
assessed instrument strength for the 122 SNPs, a function
of magnitude and precision of their genetic effect, using the
F statistic .
SNP-lung function association estimates
Three studies were used to estimate the association of the
122 SNPs with lung function in adult women: European
Community Respiratory Health Survey (ECRHS) ,
Northern Finland Birth Cohort of 1966 (NFBC 1966) ,
and UK Biobank  (Table 1). ECRHS is a European
prospective cohort study designed to identify risk factors
for respiratory health . The study started in 1992
(ECRHS I), with follow-up performed twice (ECRHS II
and III) over the following 20 years. Here we include 1069
women aged 27–57 recruited at random from
populationbased sampling frames in 14 centres, and who had lung
function measured in ECRHS II. Genetic associations
analyses for the 122 SNPs with FVC and FEV1/FVC were
adjusted for age, age2, height, centre and ancestry principal
components. NFBC1966 is a birth-cohort study performed
in the Finnish provinces of Oulu and Lapland. Pregnant
women with expected date of delivery in 1966 were
recruited and their offspring followed up . Among the
offspring, we include 2680 women with spirometry data at
age 31. Analyses were adjusted for height and ancestry
principal components. UK Biobank is a prospective study
across 22 assessment centres, aimed at identifying causes
of chronic disease in middle and old age . We include
43,195 women of European ancestry aged 40–69 recruited
in 2006–2010, who had GWA and lung function data.
Analyses were adjusted for age, age2, height, and ancestry
principal components, as well as smoking pack-years
because part of the sample was ascertained by smoking
We used two studies to estimate the association of the
122 SNPs with lung function in adolescent girls: Avon
Longitudinal Study of Parents and Children (ALSPAC)
 and Northern Finland Birth Cohort of 1986 (NFBC
1986)  (Table 1). ALSPAC is a birth-cohort study that
initially enrolled 14,541 pregnant women in Bristol, United
Kingdom, in 1990–1992 . We include 1234 of their
daughters, aged around 16, with GWA and spirometry data.
Analyses were adjusted for height; ancestry principal
components were not included because there was no
evidence of population stratification in the study. NFBC 1986
is a Finnish birth-cohort study that followed up 9432 live
births to mothers in Oulu and Lapland. A total of 6642
adolescents aged 16 participated in the clinical examination
in 2001–2002, and here we include 1791 with available
GWA and lung function data . Analyses were adjusted
for height and ancestry principal components. For both
ALSPAC and NFBC 1986, robust standard errors were
Table 1 Characteristics of the study populations included for the SNP-lung function associations
Values reported are mean (standard deviation)
used for the analyses of FEV1/FVC to account for deviation
from normality of the regression residuals.
Spirometry methods for all studies are reported in
Supplementary Table 1. For adults and adolescents,
estimates of the association with FVC and FEV1/FVC for each
SNP were pooled across studies using fixed-effect
inversevariance weighted meta-analysis.
Mendelian randomization estimates
We used a two-sample MR approach for summary data
with multiple instruments, where the estimate of the causal
effect is obtained as the inverse-variance weighted
combination of individual MR estimates across instruments,
using fixed-effect meta-analysis . Individual MR
estimates for the 122 SNPs were derived using the Wald
estimator (ratio of SNP-lung function estimate over
SNPage at menarche estimate), with standard error derived
using the delta method .
Investigation of pleiotropy
A fundamental assumption of MR is the absence of
pleiotropy, i.e. the genetic instruments modify lung
function only through age at menarche and no other
independent pathways . We tested for statistical evidence of
pleiotropy by using between-instrument heterogeneity as a
proxy; in the absence of pleiotropy, all variants are valid
instruments and their MR estimates will vary only by
chance (no heterogeneity) . We defined evidence of
pleiotropy as an I2 [ 25%, where I2 describes the
percentage of total variation in MR estimates due to
heterogeneity rather than chance , or a statistically significant
heterogeneity Cochran Q test (p \ 0.05). If pleiotropy was
detected, we performed a series of sensitivity analyses to
Using the PhenoScanner, a curated database of publicly
available GWA findings created to inform MR studies
(available at www.phenoscanner.medschl.cam.ac.uk/phe
noscanner) , we first checked for previous associations
of the 122 SNPs (and highly correlated SNPs; linkage
disequilibrium r2 [ 0.8) with any phenotype other than age
at menarche, limiting our search to associations that had
been identified at a significance level of 5 9 10-8
(Supplementary Table 2). For the exclusion of possible
pleiotropic SNPs in our sensitivity analyses, we then only
considered effects on phenotypes which can be related to
lung function. We adjusted for height all SNP-lung
function analyses and therefore height could not directly induce
pleiotropy. However, height SNPs could be associated with
other markers of somatic growth, potentially exerting
pleiotropic effects on lung function other than through
height. To test this, we excluded SNPs previously
associated with height. We then additionally excluded
SNPs previously associated with obesity and related traits
(weight, BMI, waist circumference), fasting insulin and
type 2 diabetes, and birth weight, since these might also
influence lung function. These exclusions were used in
sensitivity analyses if there was statistical evidence of
If statistically significant heterogeneity remained after
the exclusion of these SNPs, we performed two further
sensitivity analyses: a meta-analysis of MR estimates using
a random-effects model instead of the fixed-effect model
used in the main analysis , and MR-Egger regression
. The random-effects model allows for random
pleiotropic effects across SNPs, while MR-Egger regression
provides unbiased results if pleiotropic effects are not
random (i.e. do not cancel). Both analyses assume that the
magnitude of the pleiotropic effects is independent of the
magnitude of the corresponding SNP-age at menarche
effects. As these approaches are less powerful than the
fixed-effect meta-analysis, particularly the MR-Egger
regression , they were only used as further sensitivity
analyses when between-instrument heterogeneity was still
present after excluding possible pleiotropic SNPs.
In order to understand whether the observed effects of
age at menarche on FVC were due to factors specific to
menarche rather than puberty in general, we tested the
association of our 122 SNPs with lung function in men.
Many of the age at menarche SNPs that we used as
instruments have also been shown to regulate male
pubertal timing as measured by Tanner stage .
Finding evidence of an association in men would
indicate that the underlying mechanism is related to general
timing of puberty as opposed to a female-specific effect.
SNP–FVC associations in adolescent boys (N = 3421)
and adult men (N = 40,687) were estimated from the
same studies used for women (Supplementary Table 6).
For each SNP, association estimates were pooled across
studies using fixed-effect inverse-variance weighted
meta-analysis. The individual SNP–FVC estimates were
then meta-analysed (fixed-effect model) to provide an
overall effect of the 122 SNPs on FVC, which is
equivalent to performing an unweighted allele score
analysis with all SNPs.
All analyses were performed using Stata 14 (StataCorp
Imputed genotype data for the 122 SNPs were available for
all studies, with the exception of one SNP (rs10423674) in
NFBC 1986. The quality of imputation was very good for
all SNPs across all studies (imputation INFO or R2
parameters C 0.8), except for one SNP in two studies
(rs17233066, R2 of 0.4 in ECRHS II and ALSPAC). The
SNPs identified were strong instruments for age of
menarche. F statistics ranged from 21 to 441 across
variants (Supplementary Table 3), well over the threshold of
F [ 10 usually recommended as a test for weak
instruments in MR analyses .
Individual estimates of the per-allele effects on age at
menarche and lung function (FVC and FEV1/FVC) for
each SNP are provided in Supplementary Tables 3 and 4,
respectively. MR estimates for the causal effect of age at
menarche on lung function obtained separately from each
SNP are presented in Supplementary Table 5, while the
combined MR estimates across the 122 SNPs are reported
in Table 2.
The MR estimate for age at menarche and FVC in adult
women showed a statistically significant increase of
24.8 mL per year increase in age at menarche (95%
confidence interval 1.8–47.9; p = 0.035), while we found no
effect for FEV1/FVC (Table 2). In the MR analysis for
FVC, a between-instrument I2 of 45% (95% CI 31–55%;
p \ 0.001) suggested the presence of pleiotropy, and we
repeated the analysis after excluding SNPs with potentially
pleiotropic effects. Out of the 122 SNPs, 34 had been
previously associated with phenotypes other than age at
menarche, the large majority of which were height and
obesity-related traits (Supplementary Table 2). The first
sensitivity analysis excluding 14 SNPs associated with
height (Model 1 in Table 3) showed a larger and more
highly statistically significant MR estimate (43.6 mL;
17.2–69.9; p = 0.001). The second sensitivity analysis,
where we additionally excluded 13 SNPs associated with
other traits potentially related to lung function, showed
very similar results (Model 2 in Table 3). Since some
residual between-instrument heterogeneity remained in
both sensitivity analyses (Table 3), we performed a
random-effects meta-analysis of the MR estimates as well as
MR-Egger regression. For the random-effects
meta-analysis, results were similar to those in Table 3, with an MR
estimate of 40.7 mL (8.4–72.9; p = 0.013) for Model 1,
and 40.3 mL (5.7–74.8; p = 0.022) for Model 2.
MR-Egger regression, which suffers from low statistical power
, showed results in the same direction but with much
larger confidence intervals and loss of statistical
significance (Model 1: 95.7 mL, -37.0 to 228.4, p = 0.156;
Model 2: 84.8 mL, -52.2 to 221.8, p = 0.222).
In adolescents, the MR analysis for FVC showed a
statistically significant decrease of 56.5 mL per year
increase in age at menarche (95% CI -108.3 to -4.7;
p = 0.033), with no evidence of pleiotropy across the 122
SNPs (Table 2). As with adults, there appeared to be no
causal effect of age at menarche on FEV1/FVC.
Table 2 MR estimates for the
causal effect of age at menarche
on lung function in adults and
adolescents, obtained by
fixedeffect meta-analysis of
SNPspecific MR estimates across the
24.8 (1.8 to 47.9) 0.035
-56.5 (-108.3 to -4.7) 0.033
Beta, estimate of effect of 1 year increase in age at menarche on FVC (mL) and FEV1/FVC (%); I2 (%),
between-instrument heterogeneity; Het. p value, Q test p value
Bold values indicate statistically significant p values
Table 3 Sensitivity analyses for the MR of age at menarche and FVC in adult women
Model 1 Excluding SNPs previously associated with height
Model 2 Excluding SNPs previously associated with height, obesity, weight,
BMI, waist circumference, fasting insulin, type 2 diabetes, or birth weight
Reported are MR estimates after excluding SNPs with possible pleiotropic effects (Suppl. Table 2). Beta, estimate of effect of 1 year increase in
age at menarche on FVC (mL); I2 (%), between-instrument heterogeneity; Het. p value, Q test p value
Bold values indicate statistically significant p values
43.6 (17.2–69.9) 0.001
42.9 (14.7–71.2) 0.003
The results of the secondary analyses in men were very
consistent with those in women, with a statistically
significant positive association of the 122 SNPs with FVC in
adult men (p = 0.013) and a statistically significant
negative association in adolescent boys (p = 0.007).
Our study shows a causal effect of age at menarche on lung
function using Mendelian randomization, a technique
which draws on the biological principle that genes are
randomly allocated at conception to provide evidence not
affected by classical confounding. We found an effect of
age at menarche on restrictive lung impairment (FVC),
with no evidence of an effect on airway obstruction (FEV1/
FVC). In particular, we find that early menarche increases
FVC in adolescence but decreases it in adulthood. The
findings for adult women confirm previous observational
evidence suggesting a decrease in FVC of 123 mL (95% CI
27–220; p = 0.01) associated with early menarche
(menarche B10 years vs. menarche at 13), but no association
with FEV1/FVC (p = 0.77) .
The finding of a beneficial effect of earlier age at
menarche on FVC in adolescence, as opposed to the
detrimental effect in adulthood, is interesting and has a
plausible explanation, illustrated graphically in Fig. 1.
Lung development tends to plateau following menarche
, and therefore earlier initiation of menstruation may
lead to premature completion of lung development and
lower maximally attained lung function. Given the relative
stability of lung function over time (a phenomenon known
as ‘‘tracking’’) , this would translate to lower FVC in
Fig. 1 Graphical representation of a possible explanation for the
discrepancy in FVC findings for adult women and adolescent girls.
Earlier menarche may have current benefits to the lung function in
adolescents, but may also lead to premature completion of lung
development with attainment of a lower maximal lung function in
adulthood. Our secondary analysis suggests that the same
happens in males, where lung development has also been
shown to plateau at puberty . The beneficial effect of
earlier menarche on FVC in adolescent girls may be
explained by the prominent truncal (as opposed to limb)
growth and increased thoracic muscle strength which occur
in puberty and which contribute to higher lung volumes
. It could also be related to the direct effect of early
exposure to sex hormones, for example oestrogens, in
adolescent girls, as these have been shown to affect lung
function in humans  and animal models . Our
secondary analysis suggesting a similar effect in boys
support the hypothesis of a mechanism related to factors
associated with early pubertal timing in general rather than
specifically through female sex hormones. However, it is
also possible that the mechanisms differ in men and
women, for example through sex hormones in girls and
thoracic growth and muscle strength in boys (the latter
being more pronounced in boys ). The complex
hormonal and physiological shifts that occur in women during
menarche  make it difficult to pin-point the precise
mechanisms underlying our findings, and further research
is needed to explore them.
Our study suggests that if these same adolescents were
assessed in early adult life (once they have reached
maximal lung function), those with early menarche would have
comparatively lower FVC. Large-scale studies of lung
function with longitudinal data across the lifespan will
allow to test this hypothesis. To date few child cohorts
have lung function assessments in adolescence and at ages
associated with lung function plateau, but ongoing
consortium-based initiatives, such as STELAR  and
MEDALL , will be able to provide the relevant
Our findings offer insight into plausible
pathophysiological mechanisms underlying the effects of early
menarche on lung function impairment. Previous work has
shown an association of early menarche with greater risk
and severity of asthma [16, 45, 46], while we did not find
an effect of age at menarche on airway obstruction in either
adults or adolescents. This might be explained by an
association of early menarche with bronchial hyperactivity
through immunological and inflammatory effects [12, 47],
which would manifest as short-term reversible airway
obstruction not captured by the FEV1/FVC ratio from
single assessments in population-based studies. Our study
also highlights the importance of evaluating different lung
function parameters. Many epidemiological studies on lung
function have focused on low FEV1, which may arise from
either obstructive or restrictive lung impariment. We found
that early menarche only affects FVC, a proxy for total
lung capacity and characteristic of restrictive lung
impariment, which is a predictor of morbidity (including
cardiovascular morbidity) and mortality even in the
absence of chronic respiratory conditions .
All 122 SNPs used in our MR study were ‘‘strong’’
instruments, with strength reflecting not only the
magnitude of the genetic effects on age at menarche but also the
precision of their estimates. This is important since the use
of ‘‘weak’’ instruments can bias the MR estimate , with
such bias resulting in an attenuation of the causal effect in
the context of a two-sample MR analysis like ours . To
improve precision, we used the results from the GWA
discovery rather than replication analysis from Perry et al.
, as the former was over 20 times larger (182,416 vs.
8689). These estimates might have been affected by the
upward bias typical of the discovery stage (‘‘winner’s
curse’’) , but this is likely to be very limited in our
study given the strong p values. Moreover, any resulting
overestimation of the SNP-age at menarche association
would have pulled the MR estimate towards the null,
leading to underestimation of the true causal effect rather
than to a false positive result.
Like any other instrumental variable approach, MR
tends to suffer from limited statistical power when the
effect of the instruments on the exposure is relatively
small, as typically happens with common genetic variants
. Despite this, we were able to identify statistically
significant effects of age at menarche on FVC, although the
confidence intervals of our MR estimates are large,
particularly for adolescents where the sample size for the
genetic associations with lung function is much smaller.
MR is not affected by classical confounding
encountered in observational studies, and yet there is a form of
confounding specific to MR, pleiotropy, whereby the
genetic instrument modifies lung function through
secondary phenotypes other than age at menarche .
Heterogeneity in the MR estimates obtained from the
individual instruments can be used as a proxy for
pleiotropy . In our study there was evidence of
heterogeneity in the MR estimates for the analysis of FVC in
adults; the exclusion of SNPs with possible pleiotropic
effects, in particular SNPs previously associated with
height, showed consistent and much stronger results than
the main analysis, thus demonstrating robustness of our
findings. Height is strongly influenced by genetic and
environmental factors regulating growth and development,
and is also a strong predictor of FVC. In order to clearly
disentangle the effect of the age at menarche SNPs on FVC
from any possible effect on height, we adjusted all our
SNP-lung function analyses for height. Indeed, it is FVC
standardised for height which is clinically of interest, and
FVC is often expressed as a percentage of a normal
reference value (percent predicted) based on the individual’s
height as well as sex and age. The fact that removal of
SNPs previously associated with height reduced the
pleiotropy and made the result stronger in our secondary
analysis in adult women supports our hypothesis that these
SNPs could be associated with other markers of somatic
growth, exerting pleiotropic effects on lung function other
than through height. Robustness of our finding for FVC in
women was also confirmed by a further analysis to account
for residual pleiotropic effects using a random-effects
meta-analysis, while MR-Egger regression resulted in a
loss of statistical significance likely explained by its low
statistical power . Interestingly, there was no statistical
evidence of pleiotropy for FVC in adolescents, as shown by
an I2 of 2% for the between-instrument heterogeneity (95%
CI 0–21%; p = 0.42). A possible explanation for this is
that some of our genetic instruments may have effects on
secondary phenotypes related to lung function that only
become apparent during adult life.
A potential weakness of our study may arise from the
presence of gene-environment interactions , since our
MR analyses assume no interactions for the SNP-age at
menarche and SNP-lung function relationships. For
example, the data used in our study for the analysis of
adults and adolescents cover different ‘‘cohorts’’ of
women, potentially exposed to different environmental
exposures. ‘‘Cohort effects’’ are known to affect both age at
menarche and lung function. The MR approach is not
susceptible to confounding from environmental exposures,
including those inducing cohort effects, but they might bias
the results if they interacted with the genetic variants used
as instrumental variables . Although the practical
relevance of gene-environment interactions for our MR
analyses of age at menarche and lung function is not clear,
it remains a theoretical possibility.
Finally, our MR estimate of the effect of age at
menarche on FVC needs to be interpreted as a
populationaveraged causal effect rather than the effect for an
individual and are based on the assumption of a linear
relationship. Parametric and non-parametric methods to
address non-linearity in MR have been proposed, including
stratification of the exposure to estimate localized average
causal effects (LACE) [53, 54], although they typically
require individual-level data.
In conclusion, our study provides evidence of a causal
effect of early sexual development in women on lung
function later in life, with our secondary findings in men
suggesting a role for pubertal timing in general rather than
menarche specifically. This, together with evidence of
detrimental effects on other adverse health outcomes,
including cardiometabolic outcomes and cancer [3–8], has
public health implications given that factors predisposing
to early sexual development in women could be targeted at
a population level to contrast the secular trend towards
earlier puberty. These include a number of established
childhood life-style and social factors, such as diet and
obesity, psychological stress and deprivation, as well as
hypothesised environmental exposures, such as endocrine
disrupting chemicals (EDCs) found in many household
products . Of these, childhood obesity is the most
worrisome given the current childhood obesity epidemic.
EDCs may prove to be a substantial concern due to their
widespread presence and the potential persistence of their
effects on menarche for generations without further
exposure (transgenerational inherited effects) , although
these effects remain controversial. Our study also
illustrates the value of the MR approach, which exploits
increasingly available genetic data from large datasets, as a
tool to investigate causal effects of childhood events on
adult health, an area of epidemiological research which is
particularly problematic due to the presence of
confounding factors very difficult to measure and partly unknown.
Acknowledgements UK Biobank: This research has been conducted
using the UK Biobank Resource under Application Number 648, and
we thank the participants, field workers, and data managers for their
time and cooperation. The project used the ALICE and SPECTRE
High Performance Computing Facilities at the University of
Leicester. NFBC studies: We thank the late Professor Paula Rantakallio for
the launch of the studies, Ms Outi Tornwall and Ms Minttu Jussila for
the DNA biobanking, and the late Academian of Science Leena
Peltonen for her contribution. ECRHS study: We thank the
participants, field workers and researchers who have participated in the
ECRHS study for their time and cooperation. ALSPAC study: We are
extremely grateful to all the families who took part, the midwives for
their help in recruiting them, and the whole ALSPAC team, which
includes interviewers, computer and laboratory technicians, clerical
workers, research scientists, volunteers, managers, receptionists and
Funding This project has received funding from the European
Union’s Horizon 2020 research and innovation programme under
Grant Agreement No. 633212. IPH was supported by an MRC
programme Grant (G1000861). RG was supported by the UK Medical
Research Council (Grant Ref: G0902125). The work of MDT, IPH
and LVW was funded by a Medical Research Council (MRC)
strategic award (MC_PC_12010). MDT was supported by MRC
fellowships G0501942 and G0902313. This article presents independent
research funded partially by the National Institute for Health Research
(NIHR). The views expressed are those of the authors and not
necessarily those of the NHS, the NIHR or the Department of Health.
NFBC1966 study: NFBC1966 received financial support from the
Academy of Finland (Project Grants 104781, 120315, 129269,
1114194, 24300796, Center of Excellence in Complex Disease
Genetics and SALVE), University Hospital Oulu, Biocenter,
University of Oulu, Finland (75617), NHLBI Grant
5R01HL08767902 through the STAMPEED program (1RL1MH083268-01), NIH/
NIMH (5R01MH63706:02), ENGAGE Project and Grant Agreement
HEALTH-F4-2007-201413, EU FP7 EurHEALTHAgeing 277849,
the Medical Research Council, UK (G0500539, G0600705,
G1002319, PrevMetSyn/SALVE) and the MRC, Centenary Early
Career Award. The program is currently being funded by the
H2020633595 DynaHEALTH action and academy of Finland
EGEA-project. The DNA extractions, sample quality controls, biobank
upkeeping and aliquotting were performed in the National Public
Health Institute, Biomedicum Helsinki, Finland and were supported
financially by the Academy of Finland and Biocentrum Helsinki.
ECRHS study: This work was supported by a contract from the
European Commission (018996), Fondo de Investigacio´n Sanitaria
(91/0016-060-05/E, 92/0319, 93/0393, 97/0035-01, 99/0034-01 and
99/0034-02), Hospital General de Albacete, Hospital General Ramo´n
Jime´nez, Consejer´ıa de Sanidad del Principado de Asturias, CIRIT
(1997SGR 00079, 1999SGR 00241), and Servicio Andaluz de Salud,
SEPAR, Public Health Service (R01 HL62633-01), RCESP (C03/09),
Red RESPIRA (C03/011), Basque Health Department, Swiss National
Science Foundation, Swiss Federal Office for Education and Science,
Swiss National Accident Insurance Fund (SUVA), GSF-National
Research Centre for Environment and Health, Deutsche
Forschungsgemeinschaft (DFG) (FR 1526/1-1, MA 711/4-1),
Programme Hospitalier de Recherche CliniqueDRC de Grenoble 2000
No. 2610, Ministry of Health, Direction de la Recherche Clinique,
Ministere de l’Emploi et de la Solidarite, Direction Generale de la
Sante, CHU de Grenoble, Comite des Maladies Respiratoires de
l’Isere, UCB-Pharma (France), Aventis (France), Glaxo France,
Estonian Science Foundation, and AsthmaUK (formerly known as
National Asthma Campaign UK). ALSPAC study: GWAS data was
generated by Sample Logistics and Genotyping Facilities at the
Wellcome Trust Sanger Institute and LabCorp (Laboratory
Corportation of America) using support from 23andMe. The UK Medical
Research Council and the Wellcome Trust (Grant Ref: 102215/2/13/
2) and the University of Bristol provide core support for ALSPAC
Compliance with ethical standards
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
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