Department of Psychology, University of Helsinki
National Public Health Institute, Helsinki
Department of Psychology
Department of Public Health, University of Helsinki, Finland
Medical Research Council Epidemiology Resource Centre
Developmental Origins of Health and Disease Centre, University of Southampton, Southampton, UK
Department of Public Health, University of Helsinki, Helsinki, Finland
Correspondence: Katri Räikkönen, University of Helsinki, PO Box 9, 00014 University of Helsinki, Finland. Email: katri.raikkonen{at}helsinki.fi
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Aims To examine whether smaller birth size and shorter gestation predict depressive symptoms.
Method A total of 1371 members of a cohort born between 1934 and 1944 at term (259294 daysgestation) in Helsinki, Finland, completed the Beck Depression Inventory (BDI) and the Center for Epidemiological Studies Depression scale (CESD) at an average age of 61.5 years (BDI) and 63.4 years (BDI and CESD).
Results Gestational length predicted depressive symptoms linearly and independently of gender and birth weight: per day decrease in gestational length, depressive symptoms scores increased by 0.80.9% (95% CI 0.21.4, P<0.009). Weight, length and head circumference at birth showed no linear association with depression, adjusted for gender and gestational length. The results did not change when further controlled for socio-economic characteristics at birth and in adulthood, age and body mass index in adulthood.
Conclusions Susceptibility to depressive symptoms may relate to shorter length of gestation.
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However, challenging any programming effects on depression, a recent study found no association between birth weight and psychiatric ward admission for depression in adult men (Osler et al, 2005). Moreover, the earlier studies gave mixed results in relation to gender (Thompson et al, 2001; Cheung et al, 2002; Gale & Martyn, 2004; Patton et al, 2004). One possible explanation for the discrepancy is that, apart from studies using clinical diagnosis or hospital admission (Patton et al, 2004; Osler et al, 2005), depressive symptoms have been measured using standardised tools in only one study (Thompson et al, 2001). Finally, it is well known that low birth weight reflects not only foetal growth but also length of gestation, yet gestational length has rarely been a focus in the previous studies either this information has not been available (Thompson et al, 2001; Osler et al, 2005) or it has been available but assigned the status of a covariable (Cheung et al, 2002; Gale & Martyn, 2004). Interestingly, however, recent studies have revealed that independent of birth weight, shorter gestational length predicts increased risk of stroke, cerebrovascular disease and high blood pressure (Järvelin et al, 2004; Koupil et al 2005; Lawlor et al, 2005). This suggests that body size at birth and gestational length may both have unique predictive power and reflect foetal growth-related processes that are under different physiological controls. Thus, we tested whether smaller body size at birth and shorter length of gestation predict, independently of each other, depressive symptoms rated using the Beck Depression Inventory (BDI; Beck et al, 1988) and the Center for Epidemiological Studies Depression scale (CESD; Radloff, 1977) on two separate occasions at ages 61.5 years (BDI) and 63.4 years (BDI and CESD) among men and women born between 1934 and 1944 at term in Helsinki.
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At a mean age of 61.5 years (s.d.=2.9, range 56.769.8) time 1 a subset of 2690 (1413 women and 1277 men) were invited to participate in the clinical examination. They were selected from the initial study population using random number tables, as described by Barker et al (2005). Of this subset, 1075 women and 928 men participated. Fourteen of the non-participants had died, others declined or could not be reached. The participants were more frequently women than the non-participants (P=0.04), reflecting our initial random selection of 200 women to undergo screening for osteoporosis, and subsequent random selection of both genders. After adjusting for the gender difference, participants and non-participants did not differ significantly from each other in body size at birth (weight, length, head circumference), length of gestation, maternal characteristics (height, weight in late pregnancy) or social class at birth based on fathers occupation (all P>0.07), except that the participants had higher ponderal index (kg/m3) at birth (P=0.05) and their mothers were older (P=0.01) and had a higher body mass index (kg/m2) in late pregnancy (P=0.04) (data not shown).
At a mean average age of 63.4 years (s.d.=2.9, range=59.770.7) time 2 (mean interval between time 1 and time 2 1.9 years, s.d.=0.7, range 0.43.3) a psychological survey was sent by post to the members of the randomly selected sample who were still traceable (n=1975). Of this group, 1704 participants (951 women and 753 men) returned the survey. Of the 1664 participants having complete data available on depressive symptoms at time 1 and time 2, 1371 (752 women and 619 men) were born at term (259294 days gestation). They formed the sample of the current study: they were more likely to be women (P=0.0001), and, even after adjusting for the gender difference, they were taller as adults (P=0.005) and less depressed (P<0.002) when compared with the rest of the randomly selected subset of the randomly selected participants at time 1 born at term (data not shown). These groups did not differ from each other in body size at birth, length of gestation, in maternal characteristics (age, height, weight, body mass index in late pregnancy) or in social class at birth based on fathers occupation, or in age, weight, body mass index or level of education at time 1 (all P>0.20) (data not shown). The ethics committee of the National Public Health Institute approved this project, and all participants gave written informed consent.
Measures
The BDI (Beck et al,
1988) and the CESD
(Radloff, 1977) were used to
measure the severity and frequency of depressive symptoms. These measures are
the two most frequently used and well-validated self-report screening tools
for depressive symptoms. The BDI consists of 21 items assessing symptoms of
depression during the previous 2 weeks. Each item contains four statements
reflecting varying degrees of symptom severity. Respondents are instructed to
circle the number (03) that corresponds with the statement that best
describes them; higher scores indicate increasing severity. Ratings are summed
to calculate a total BDI score, which can range from 0 to 63. The CESD
consists of 20 items assessing the frequency of depressive symptoms during the
preceding week. Each item is rated on a four-point scale ranging from 0 (not
at all/less than a day) to 3 (all the time/57 days a week). Ratings are
summed to calculate a total CESD score, which can range from 0 to 60.
Although the BDI and the CESD are designed to screen but not diagnose
major depression, BDI cut-off scores of 10, 19 and 30 or more are indicative
of mild to moderate, moderate to severe and severe depressive symptoms
respectively, and a CESD cut-off score of 16 or more suggests more
frequent experience of depressive symptoms. The internal reliability
coefficients (Cronbachs
) of the BDI and the CESD ranged
from 0.81 to 0.91. The BDI scores measured at time 1 and time 2
(r=0.79, P<0.001) and the BDI and the CESD scores
measured at time 2 (r=0.64, P<0.001) were significantly
associated.
Data on the newborns date of birth, weight (g), length (cm) and head circumference (cm), and the mothers height (cm) and weight (kg) in late pregnancy, age and the date of the last menstrual period, as well as social class (lower, lower middle, upper middle, middle) based on fathers occupation, were extracted from birth records. Adult height (cm) and weight (kg) as well as level of education (elementary school, vocational school, senior high school, college/university degree) were measured in conjunction with the clinical examination at time 1. Body mass index (BMI) was calculated in kg/m2.
Statistical analyses
We used multiple linear regression analyses to assess the relation of body
size at birth and length of gestation with depressive symptoms. Because
depressive symptoms measured by the BDI at time 1 and time 2 were
significantly associated, and the mean level of the scores did not show
significant change over time (F(1,1369)=1.36, P=0.24 in
repeated-measures analysis of covariance adjusting for gender), the BDI scores
were averaged across time 1 and time 2 for the analyses. We adjusted for
gender and length of gestation in the analyses of body size, and for gender
and birth weight in the analyses of duration of gestation (r=0.30,
0.29 and 0.28 between duration of gestation and weight, length and head
circumference at birth respectively; all P<0.001). We repeated the
analyses after further adjusting for other factors potentially confounding the
associations, i.e. social class at birth, adult level of education, age at the
time of measuring depressive symptoms and adult BMI.
Despite the significant rank order and mean level stability of the BDI scores from time 1 to time 2, and concurrent consistency of the BDI and the CESD scores at time 2, these were not in perfect agreement. Therefore, by using logistic regressions we assessed the effect of body size at birth and length of gestation on dichotomised variables describing the consistency of depressive symptoms across time (BDI scores at time 1 and time 2) and across measures (BDI and CESD scores at time 2). By using the widely accepted cut-off points of 10 or above for the BDI (indicating at least mild symptom severity; Beck et al, 1988) and 16 or above for the CESD (indicating more frequent experience of depressive symptoms; Radloff, 1977), we compared first participants who had BDI scores of 10 or above at both time 1 and time 2 with participants whose BDI scores were below 10 on both occasions, and second, participants whose BDI and CESD scores were both at or above the cut-off points at time 2 with those who scored below these cut-off points on the two measures. The logistic regressions were adjusted for the same variables as the linear regressions described above.
We used body size at birth (weight in kg, and length and head circumference in cm) and length of gestation (days) in the analyses as continuous measures. However, because there are data suggesting that individuals born weighing 2.5 kg or less are particularly susceptible to later physical adversities and depressive symptoms (e.g. Gale & Martyn, 2004), we tested in additional analyses, whether those born weighing 2.5 kg or less differed from those weighing more than 2.5 kg in depressive symptomatology. The BDI and the CESD scores were log-transformed (log+1) to normalise the skewed distributions. However, to facilitate interpretation, exponential function was used to reconvert the coefficients. We also tested whether any of these associations varied for men and women by including interaction terms in the models. In no instance was there a significant gender interaction term (P>0.15) (data not shown). For this reason we report the results in both genders combined.
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View this table: [in a new window] | Table 1 Characteristics of the sample |
Length of gestation and depressive symptoms
Table 2 shows that, after
adjusting for gender and birth weight, depressive symptom scores increased by
0.80.9% per day decrease in length of gestation. Adjusting further for
the other confounders (social class at birth, educational attainment, age at
the time of testing, adult BMI) did not alter the magnitude of these
associations (Table 2).
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View this table: [in a new window] | Table 2 Percentage change in depressive symptom scores according to unit change in length of gestation and body size at birth |
When we compared participants whose BDI scores were 10 or above (the commonly accepted cut-off score for mild depressive symptoms) at both time 1 and time 2 (45 men and 107 women) with participants whose BDI scores were below 10 at both times (497 men and 485 women), we found that the odds of belonging to the former relative to the latter group increased significantly for each days decrease in length of gestation (OR=0.96, 95% CI 0.940.98; i.e. a 4.2% increase in risk) (Table 3). The difference was independent of gender and birth weight. Also independently of gender and birth weight, the odds of belonging to the group whose BDI and CESD scores both exceeded the cut-off points at time 2 (53 men and 108 women) rather than the group in which neither score exceeded these levels (495 men and 521 women) was increased significantly for each days decrease in length of gestation (OR=0.97, 95% CI 0.950.99, i.e. a 3.1% increase in risk). Adjusting further for the other confounders did not change these associations (Table 3).
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View this table: [in a new window] | Table 3 Comparison of length of gestation and body size at birth of individuals without (DS) and with (+DS) depressive symptoms across time and across measures. |
Body size at birth and depressive symptoms
Multiple linear regression analyses showed that after adjusting for
gender and length of gestation weight, length and head circumference
at birth showed no significant linear association with depressive symptom
scores (Tables 2 and
3). However, when we compared
participants weighing 2.5 kg or less at birth (15 men and 16 women) with those
weighing over 2.5 kg at birth (604 men and 736 women) we found that those in
the low birth weight group had 47.4% (95% CI 11.994.3,
P=0.006) higher BDI scores and 35.5% (95% CI 0.0084.2,
P=0.05) higher CESD scores, and were 3.1 times (95% CI
1.37.4, P=0.01) more likely to have BDI scores exceeding the
mild severity cut-off point at both time 1 and time 2, and 3.7 times (95% CI
1.68.6, P=0.002) more likely to have both BDI and CESD
scores exceeding mild severity and moderate frequency cut-off points at time
2, independent of gender and length of gestation. Adjusting for the other
confounders did not change these associations (P<0.02), except
that association with CESD scores was rendered non-significant
(P=0.07) (data not shown). Figure
1 compares the BDI and the CESD scores for the two
birth-weight groups.
![]() View larger version (12K): [in a new window] [as a PowerPoint slide] |
Fig. 1 Beck Depression Inventory (BDI) and Center for Epidemiological Studies
Depression scale (CESD) scores (means and 95% confidence
intervals) according to birth weight (n=31, n=219,
n=562, n=433, n=104 and n=22 for the six
categories from the lightest to the heaviest group respectively).
Log-transformed depressive symptom scores have been adjusted for gender,
length of gestation, social class at birth, educational attainment, age and
body mass index in adulthood, and then back-transformed to the original scale
for display.
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Our results indicate that length of gestation, at term range of gestation,
consistently predicted depressive symptoms later in life. Although the
associations were not large in magnitude 0.80.9% increase in
depressive symptoms per day decrease in gestational length they
represent effects that are continuous and not accounted for by birth weight or
gender, or by social class at birth, educational attainment, age at the time
of testing or BMI score in adulthood. Further, the risk of depressive symptom
scores staying above the cut-off point of mild severity (BDI
10) for a
mean period of 2 years (range 0.43.3) was increased by over 4%, and
above the cut-off points of mild severity (BDI
10) and moderate frequency
(CESD
16) on the two measures concurrently was increased by over 3%
per day decrease in gestational length. These effects were not accounted for
by birth weight, gender or the other covariates.
After adjusting for gender and length of gestation there was no association between any measure of depressive symptoms and the full range of variation in birth weight, length and head circumference. However, after adjusting for gender and length of gestation, a comparison of those whose birth weight was 2.5 kg or less with those born weighing over 2.5 kg showed that the former scored significantly higher on depressive symptoms, had a 3.1 times greater risk of experiencing increased depressive symptoms over time and a 3.7 times greater risk of experiencing increased depressive symptoms across measures. These associations did not change when adjusting further for social class at birth, educational attainment, age at the time of testing and adult BMI.
An association between lower birth weight and depression, evaluated at the age of 68 years by means of the self-reported Geriatric Depression Scale and the Geriatric Mental State semi-structured interview conducted by trained research nurses, has been shown among men born in Hertfordshire, England (Thompson et al, 2001). However, the data from the Hertfordshire cohort did not include length of gestation, and thus it remains unclear whether the association is attributable to slower intrauterine growth, shorter length of gestation, or both. A role of slow intrauterine growth is argued for by studies in 26-year-old women (Gale & Martyn, 2004) and in women and men at ages 23, 33 and 42 years (Cheung et al, 2002) showing that the association between lower birth weight and depressive symptoms, measured by the self-reported Malaise Inventory (Rutter et al, 1970) is present even though slightly weakened after adjustment for gestational length. Associations between gestational length and depression were not, however, reported in these studies (Cheung et al, 2002; Gale & Martyn, 2004). Together with the results of our study, these findings suggest that mechanisms linking early environment with late-life susceptibility to depressive symptoms might include mechanisms leading to shorter duration of gestation as well as those related to slower intrauterine growth.
Early physiological adaptation particularly of the hypothalamic pituitaryadrenal (HPA) axis to hormonal responses, to maternal-foetal malnutrition and to other adverse intrauterine events may lie beneath the associations. Supporting the role of maternalfoetal undernutrition in mental ill health are findings from the Dutch Hunger Winter of 19441945, showing that male and female foetuses exposed to famine during middle to late gestation may experience major affective disorders in adulthood (Brown et al, 1995, 2000). In support of a role for hormonal mechanisms, altered activity of the HPA axis is among the most consistently demonstrated biological abnormalities in depression (Brown et al, 2004); this hormonal axis is involved in the timing of parturition (McLean & Smith, 2001) and increased activity of the axis in adulthood characterises individuals who were born earlier in gestation and smaller (Phillips et al, 2000; Kajantie et al, 2002). Other hormonal mechanisms may be involved as well. Nor can we rule out genetic mechanisms: there is evidence that depressive symptoms are at least moderately heritable (Agrawal et al, 2004). Evidence also exists linking maternal prenatal distress with shorter length of gestation (Glynn et al, 2001) and with less optimal psychological development of the offspring (OConnor et al, 2003; Van den Bergh et al, 2005). Thus, the association found between shorter length of gestation and depressive symptoms might reflect an underlying genetic mechanism: mothers with depression might through associated hormonal mechanisms be predisposed to earlier parturition, and the more severe and intense depressive symptoms in the offspring might reflect the heritable component of this disorder. Further support for a role for genetic mechanisms is provided by a recent study of twins aged 817 years in which a greater increase in depressive symptoms per unit decrease in birth weight was reported for individuals at genetic or familial risk of depression (Rice et al, 2006). Although the study adjusted birth weight for gestation, the effect of length of gestation per se was not studied (Rice et al, 2006).
Furthermore, our findings on the foetal origins of depressive symptoms may shed some light on the associations between depressive symptoms and increased risk of cardiovascular disease, type 2 diabetes (Evans et al, 2005) and the various risk factors for these diseases (Räikkönen et al, 2002). As proposed by Thomson et al (2001) it is indeed probable that depression and the associated disease risk share a common underlying basis that might be attributable to a less than optimal foetal environment.
Limitations
There are limitations to our study. In 19341944 gestation was
estimated by the date of the last menstrual period, which might make the
length of gestation, even at the term gestational range, as well as body size
adjusted for gestational length, to some extent imprecise. Although this
introduces inaccuracy, misclassification of gestational age would only weaken
our ability to detect associations with depression in adulthood. Moreover,
length of gestation and body size at birth are affected by many factors that
could have long-term neurodevelopmental consequences; however, the data
available to us do not allow detailed evaluation of the specific
pathophysiological mechanisms that are reflected by these proxies. Cohort
members who died before 1971 were excluded from our survey. Loss of follow-up
across decades is also inevitable. However, over 86% of the randomly selected,
still traceable cohort members were available for the psychological survey.
Participation in the follow-up was more frequently related to female gender
and (even after adjusting for this difference) to lower level of depressive
symptoms. Participation in follow-up was not, however, related to any of the
neonatal or maternal characteristics. Finally, the age range of the sample
ought to be considered in light of external validity of the findings, as
depressive symptoms in later and in earlier life may differ.
We conclude that implications of earlier birth and smaller body size at birth persist into later adulthood. These results confirm earlier studies relating birth weight to symptoms of depression (Thompson et al, 2001; Cheung et al, 2002; Gale & Martyn, 2004; Patton et al, 2004). Moreover, they add to the previous literature by showing that independently of birth weight, shorter length of gestation at the term gestational age range shows continuous associations with depressive symptoms, and may thus serve as another marker of early environmental influences in the cascade of events leading to more severe and frequent depressive symptoms later in life.
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