To examine the association between body size and depression in a longitudinal setting and to explore the connection between obesity and depression in young adults at the age of 31 years.
This study forms part of the longitudinal Northern Finland 1966 Birth Cohort Study (N=12 058). The follow-up studies were performed at 14 and 31 years. Data were collected by postal inquiry at 14 years and by postal inquiry and clinical examination at 31 years.
A total of 8451 subjects (4029 men and 4422 women) who gave a written informed consent and information on depression by three depression indicators at 31 years.
Body size at 14 (body mass index (BMI) and 31 (BMI and waist-to-hip ratio (WHR)) years and depression at 31 years by three different ways: depressive symptoms by the HSCL-25-depression questionnaire (HSCL-25), the use of antidepressants and self-reported physician-diagnosed depression.
Obesity at 14 years associated with depressive symptoms at 31 years; among male subjects using the cutoff point 2.01 in the HSCL-25 (adjusted odds ratio (OR) 1.97, 95% CI 1.06–3.68), among female subjects using the cutoff point 1.75 (adjusted OR 1.64, 95% CI 1.16–2.32). Female subjects who were obese both at baseline and follow-up had depressive symptoms relatively commonly (adjusted OR 1.40, 95% CI 1.06–1.85 at cutoff point 1.75); a similar association was not found among male subjects. The proportion of those who used antidepressants was 2.17-fold higher among female subjects who had gained weight compared to female subjects who had stayed normal-weighted (adjusted OR 2.17, 95% CI 1.28–3.68). In the cross-sectional analyses male subjects with abdominal obesity (WHR 85th percentile) had a 1.76-fold risk of depressive symptoms using the cutoff 2.01 in the HSCL-25 (adjusted OR 1.76, 95% CI 1.08–2.88). Abdominally obese male subjects had a 2.07-fold risk for physician-diagnosed depression (adjusted OR 2.07, 95% CI 1.23–3.47) and the proportion of those who used antidepressants was 2.63-fold higher among obese male subjects than among male subjects without abdominal obesity (adjusted OR 2.63, 95% CI 1.33–5.21). Abdominal obesity did not associate with depression in female subjects.
Obesity in adolescence may be associated with later depression in young adulthood, abdominal obesity among male subjects may be closely related to concomitant depression, and being overweight/obese both in adolescence and adulthood may be a risk for depression among female subjects.
The prevalence of obesity has been increasing both among adults and children in Western countries.1, 2, 3 Obesity is a risk factor for many physical diseases, such as type 2 diabetes4 and cardiovascular diseases,5 and can lead to premature death.6 Especially abdominal obesity, as estimated by the waist-to-hip ratio (WHR), is associated with type 2 diabetes mellitus, cardiovascular disease and stroke.7, 8
Depression is also a common public health problem, and it has been shown to be associated with many somatic disabilities such as cardiovascular diseases and type 2 diabetes.9, 10 In cardiovascular diseases, depression increases mortality and morbidity by mechanisms that are still unclear.11, 12 Less is known about the association between obesity and psychological health. ‘The Jolly Fat’ -hypothesis was presented in the 1970s, when a positive association was found between obesity and low levels of anxiety in men and women, and low levels of depression in men.13 On the other hand, recent studies have mostly observed an increased risk for depression among the obese.14, 15
Most of the epidemiological studies concerning the association between obesity and depression have been cross-sectional.15, 16 There is not much knowledge of whether obesity increases the risk of depression in later life. One of the few follow-up studies with prospectively collected data found that obesity predicted depression in a 1-year follow-up, when other variables were controlled.15 Roberts et al.17 found in a two-wave, 5-year observational study of 2123 subjects 50 years and older from the Alameda County Study data, that obesity at baseline was associated with increased risk of depression 5 years later, and that depression did not increase the risk of future obesity. Another recent study investigating the association between obesity and eight indicators of mental health using community residents 50 years and older showed that obese subjects were at increased risk for depression 5 years later.18 Noppa and Hällström19 followed a sample of middle-aged women for a 6-year period and found that women who were more severely depressed at baseline were at greater risk for weight gain. A positive correlation between abdominal obesity and depressive symptoms was previously observed in a study of 59 middle-aged men.20
The aim of the present study was to examine the association between body size and depression in a longitudinal setting in the Northern Finland 1966 Birth Cohort (NFBC 1966). We evaluated first whether obesity in adolescence (at the age of 14 years) predicts depression in young adulthood (at the age of 31 years) and secondly whether depression is more common among the obese than among those with normal weight at the age of 31 years. In addition, we explored the connection between abdominal obesity and depression in young adults at the age of 31 years and studied whether gaining weight from age 14 to 31 is associated with depression.
This study forms part of the prospective NFBC 1966. The original sample was collected from a geographically defined area of the two northernmost provinces of Finland. It consists of an unselected birth cohort of 12 058 live births, and covered 96.3% of all deliveries in Northern Finland in the year 1966.21 All subjects are Caucasians. Data collection was begun in the antenatal phase and it has been continued since then in several ways. The follow-up studies were performed at the age of 14 and 31 years. At the age of 14 years, the follow-up study was conducted solely by postal inquiry. At the age of 31 years, both postal inquiry and clinical examination were used. The study was approved by the Ethical Committee of Oulu University Faculty of Medicine. Written informed consent was obtained from all participants.
At the age of 14 years, 11 780 subjects were alive (Figure 1). In a postal questionnaire information was obtained on both height and weight of 10 096 subjects. We had information on the depression indicators at the 31-year follow-up study of 3524 male subjects and 3988 female subjects who returned the questionnaire at the age of 14 years.
In 1997–1998, a 31-year follow-up study was conducted by means of a postal inquiry to 11 541 members of the cohort. Data were obtained on height, weight and depression indicators of 4019 male subjects and 4374 female subjects. At the time, 8465 cohort members who were still living in northern Finland or in the capital area of Helsinki were invited to a clinical examination in which weight, height and WHR were measured. Data were available both of WHR measured in the clinical examination and depression indicators obtained from the postal inquiry of 2793 male subjects and 2893 female subjects.
Of the 10 096 subjects of whom we had data on both weight and height at the age of 14 years, 2584 did not participate in the present study (information of depression was missing). Among male subjects lost to follow-up obesity was more prevalent than among participating male subjects (7.0% obese vs 5.0% obese, P=0.02). In female subjects, no significant differences were found.
Overweight and obesity were assessed by the body mass index (BMI), kg/m2. The postal questionnaire sent to the subjects at the age of 14 included questions about weight (kg) and height (cm). BMI at the age of 14 years was calculated for each individual. At the age of 14 years, overweight was defined as BMI between the 85th and the 95th percentiles separately for male subjects (N=347, BMI=21.45–23.42 kg/m2) and female subjects (N=402, BMI=21.63–23.80 kg/m2), and obesity was defined as BMI at or above the 95th percentile separately for male subjects (N=177, BMI 23.43 kg/m2) and female subjects (N=200, BMI 23.81 kg/m2), respectively. We used an internal definition, based on percentiles, to provide sufficient numbers for the analyses as has been performed in previous studies on adolescent obesity and also in this sample.14, 22
BMI at the age of 31 years was calculated using the measured data of body weight (kg, in underwear) and height (cm, without shoes) obtained during the clinical examination or the weight and height asked in the questionnaire if the measured data from the clinical examination were not available. In 70% of the subjects weight and height were measured. The self-reported and measured weight and height were almost identical (Pearson's correlation r=0.98). The subjects were classified into four BMI categories according to the standard international classification (WHO 1998): underweight <18.5 kg/m2, normal weight 18.5–24.9 kg/m2, overweight 25.0–29.9 kg/m2 (1586 male and 908 female subjects), and obese 30.0 kg/m2 (344 male and 378 female subjects). These limits were the same for both male and female subjects. Additionally, circumferences of waist (cm, at the level midway between the lowest rib margin and the iliac crest) and the hip (cm, at the widest trochanters) were measured during the clinical examination. Abdominal obesity was defined by the sex-specific WHR of the 85th percentile or greater (cutoff for male subjects 97.0 cm and for female subjects 87.7 cm).
Weight change was studied as dividing the subjects into three groups: ‘always overweight’, who were overweight or obese both at the ages of 14 and 31 years; ‘gained weight’, who had normal weight at the age of 14 years and overweight or obese at the age of 31 years; and ‘the others’ who had normal weight at the age of 14 and 31 years. There were only 82 male subjects and 186 female subjects who had lost weight. That is why they were combined with those who were normally weighted both at the age of 14 and 31 years.
Depression was defined in three different ways at the age of 31 years. Current depression was assessed by the HSCL-25-depression questionnaire, which is a 25-item shortened version of an originally 90-item questionnaire designed by Derogatis et al.23 The HSCL-25-questionnaire contains a 13-item depression subscale.24, 25 In this subscale, the subject assesses the presence and intensity of depressive symptoms over the previous week. The answers are scored on a scale from 1 (not bothered) to 4 (extremely bothered). The HSCL-score is the sum of items divided by the number of items answered. We used three different cutoff points to define depression: 1.55, 1.75 and 2.01. As reference population for depression, we used subjects with no depressive symptoms according to the HSCL-25, HSCL-score <1.55. The HSCL-25 has been previously found to be a valid instrument for screening psychiatric cases in the Nordic countries, including Finland.26 Secondly, the subjects were asked in the questionnaire about their current use of antidepressants (yes/no). Thirdly, self-reported lifetime-depression was defined by asking the subjects in the questionnaire whether they had ever been diagnosed by a physician as having depression (yes/no).
We selected the confounders according to the existing literature concerning the available data in the 14-and 31-year follow-up phases of this project. Depression has been found to be associated with socioeconomic status,27 marital status and family type,28 chronic somatic diseases,28 smoking,28 use of alcohol,28 physical activity29, 30 and dietary habits.31 Obesity has also been found to be associated with socioeconomic status,27 marital status and family type,32 chronic somatic diseases,33 smoking,34 use of alcohol,35 physical activity36 and dietary habits.35 For the longitudinal analyses, we used the following confounders from the 14-year follow-up phase: father's social class, family type (single-parent family/two-parent family), chronic somatic diseases (asthma, rheumatoid arthritis, diabetes mellitus, epilepsy, thyroid diseases, hypertonia, leukaemia, kidney diseases, haemophilia), smoking (yes/no) and use of alcohol. For the cross-sectional analyses, we used the following confounders from the 31-year follow-up phase: subjects’ own level of education as an indicator of socioeconomic status (basic/secondary/tertiary level), marital status (not married or cohabiting/married or cohabiting), chronic somatic diseases (hypertonia, congenital heart failures, angina pectoris, diabetes mellitus, thyroid diseases, ulcer, epilepsy, rheumatoid arthritis, cancer), smoking (no/yes), use of alcohol (no to light, moderate, heavy), physical activity (regular/nonregular), dietary habits (healthy/unhealthy). The selection of chronic somatic diseases depended on the availability of data. We included all chronic somatic diseases that were available in the data set separately in the 14-year follow-up phase and in the 31-year follow-up phase.
The statistical analyses were performed using the SPSS system version 11.5 for Windows.37 As a preliminary method to study the association between variables we used cross-tabulation, using Pearson's χ2 test for independence to evaluate statistical significance. Multivariate binary logistic regression analyses were used to explore the overweight/obesity–depression associations adjusting for the confounding variables to get adjusted ORs.
The prevalence of depression measured by the HSCL-25 using the cutoff point 1.75 was 11.6% among male subjects (N=468) and 17.2% among female subjects (N=761). Of the male subjects, 72 (1.8%) and of the female subjects, 76 (1.7%) were using antidepressants at the time of the clinical examination. Of the male subjects using antidepressants, 34 reported the type of the antidepressant, including six cases (17.7%) using tricyclic or other antidepressants causing weight gain. Of the female subjects using antidepressants, 49 reported the type of the antidepressant, including eight cases (16.3%) using tricyclic or other antidepressants causing weight gain. Depression had been diagnosed by a physician in 146 (3.6%) male subjects and in 233 (5.3%) female subjects.
BMI at the age of 14 years and depression at the age of 31 years
Obesity at the age of 14 years associated with depressive symptoms at the age of 31 years; among male subjects using the cutoff point 2.01 in the HSCL-25 (adjusted OR 1.97, 95% CI 1.06–3.68), among female subjects using the cutoff point 1.75 (adjusted OR 1.64, 95% CI 1.16–2.32) (Table 1). Overweight or obesity did not associate statistically significantly with physician-diagnosed depression or the use of antidepressants in adulthood.
BMI at the age of 31 years and depression at the age of 31 years
In the cross-sectional analyses of 31-year-old male subjects, we found that underweight men had a 2.48–6.10-fold risk of having depressive symptoms compared to men with normal weight when using different HSCL-cutoff points (Table 2). The finding remained significant using the cutoff point 2.01 when the analyses were adjusted for potential confounders. Overweight was not statistically significantly associated with HSCL-depression among male subjects. Overweight or obesity was not statistically significantly associated with physician-diagnosed depression among male subjects. The proportion of those who used antidepressants was 2.49-fold higher among obese than among normal-weighted men, and this association remained significant after adjusting for the confounders (OR 2.21, 95% CI 1.12–4.37).
Among the female subjects, there were no statistically significant associations between obesity or overweight and depression measured by the HSCL-questionnaire. The proportion of those who used antidepressants was 2.63-fold higher among the underweight women than women with normal weight, but the finding did not remain significant after adjusting for the confounders (OR 2.49, 95% CI 0.85–7.27). The proportion of those who used antidepressants was 2.18-fold higher among obese women than among normal-weighted women, although this finding did not reach statistical significance after adjusting for the confounders (OR 2.00, 95% CI 0.95–4.19). Obesity or overweight among female subjects was not associated with physician-diagnosed lifetime depression.
Abdominal obesity at the age of 31 years and depression at the age of 31 years
Among men, abdominal obesity, as estimated by the WHR 85th percentile, was statistically associated with depression at all HSCL-cutoff points (Table 3). Compared to subjects with no abdominal obesity, the abdominally obese men had a 1.67–2.64-fold risk for depressive symptoms. After adjusting for the confounders the association remained significant at the cutoff point 2.01.
After adjusting for the confounders, obese men had a 2.07-fold risk for physician-diagnosed depression (adjusted OR 2.07, 95% CI 1.23–3.47) and the proportion of those who used antidepressants was 2.63-fold higher among obese men than men without abdominal obesity (adjusted OR 2.63, 95% CI 1.33–5.21). In female subjects, no association was found between abdominal obesity and depression after adjusting for confounders.
Weight change and depression at the age of 31 years
Among male subjects, no associations between weight change and depression were found. Among female subjects, always overweight subjects had 1.5 times more commonly current depressive symptoms in the HSCL-questionnaire at all cutoff points compared to normal-weighted subjects. The result was significant after adjusting for the confounders at cutoff-points 1.55 and 1.75 (Table 4). The proportion of those who used antidepressants was 2.17-fold higher among women who had gained weight than women who had stayed normal weighted (adjusted OR 2.17, 95% CI 1.28–3.68). Weight gain or being always overweight was not associated with physician-diagnosed depression among women.
The main findings in this longitudinal NFBC 1966 study were that teenage obesity predicted depression in young adults, obesity and especially abdominal obesity among male subjects was associated with concomitant depression in adulthood and being overweight/obese both at the age of 14 and 31 years was associated with depression among female subjects.
To our knowledge, there are very few longitudinal studies in which associations between obesity and depression have been looked at. In an earlier study, depression in adolescence was observed to be associated with an increased BMI in adulthood, even when participants with childhood obesity were excluded at baseline.38 A recent study showed that depressed adolescents were at increased risk of obesity in a 1-year follow-up.14 This study gives the assumption, similarly to Roberts et al.,15, 17, 18 that obesity predicts later depression. A thin and beautiful body is idealized among adolescents, especially among girls. Body image develops at adolescence, and at that age overweight or obesity may easily have a negative influence on subjective well-being. However, since depressive symptoms in adolescence are known to be associated (perhaps causally) with obesity in adolescence, the lack of measurement of this factor at the age of 14 years makes it impossible to assess whether it is merely depression in adolescence which predicts recurrent/persistent depressive symptoms at the age of 31 years, rather than obesity at the age of 14 years. Additionally, the existing longitudinal studies on obesity and its social and economical consequences seem to focus more on women than men.39, 40
In a cross-sectional setting, underweight men (BMI under 18.5 kg/m2) were more commonly depressed than those with normal weight at the age of 31 years; there was a parallel increase in the ORs with increasing severity of depressive symptoms. Carpenter et al.41 found among men an association between being underweight and having an increased risk of clinical depression and suicidal tendencies. Thus, being underweight and male may have a special psychological meaning: men may prefer a large, muscular body rather than a thin one, and having a low body weight may be associated with a poorer body image and may also increase the risk for depression. In addition, as weight loss is one possible symptom of depression the possibility of bi-directional causality must be taken into consideration. Depression may cause weight loss by reduced appetite, being underweight may thus also be a consequence of depression.
The connection between abdominal obesity and depression in men was found by all three depression indicators. A possible mechanism behind abdominal obesity and depression may be stress.42, 43, 44, 45 A possible physiological mechanism behind abdominal obesity and depression may be cortisol secretion, which is regulated by the hypothalamic–pituitary–adrenal axis.42, 43 Increased levels of cortisol have been observed during stress44 and depression.45 As a way to cope with stress some individuals are prone to consume alcohol and to eat unhealthy foods,22 which is associated with abdominal obesity35 and depression.46 This was supported in this study by the observation that crude ORs decreased when analyses were controlled for unhealthy behaviours. Physical inactivity is also closely related to the development of abdominal obesity35, 47, 48 and physical inactivity may decrease psychological well-being.29 Regular physical activity is associated with psychological well-being due to increased secretion of endorphins after exercise.30 Unhealthy dietary habits involving, for example, infrequent consumption of fruit, berries and vegetables have been shown to be associated with abdominal obesity.35 These foods are rich, for example, in folic acid, and their low intake may predispose to psychiatric disorders such as depression.31 Additionally, infrequent consumption of fish resulting in a low intake of w-3 fatty acids has been shown to be associated with depression.49 On the other hand, depressed subjects might have poor appetite, and their diet might be inadequate and unbalanced. Abdominal obesity might thus be an indicator of unhealthy habits associated with depression, but the direction of the causality between abdominal obesity and depression cannot be exactly assessed in this cross-sectional study setting.
The use of antidepressants was quite rare compared to the result from the HSCL-questionnaire. In the HSCL-25, the prevalence of depression was 12% in male subjects and 17% in female subjects, while only 2% of male and female subjects used antidepressants. The subjects using antidepressants probably had more severe depression than those having depressive symptoms measured by the HSCL. That is also why the results are somewhat inconsistent depending on the assessment of depression. An association between weight gain and depression was found among women who used antidepressants. Some antidepressive drugs such as tricyclics often produce weight gain, while serotonergic antidepressants do not cause weight gain.50 The proportion of the users of the antidepressants was also high among men with abdominal obesity. The antidepressants may have contributed to the increase in abdominal fat, although in this study most of the subjects who reported the type of the antidepressant did not use drugs causing weight gain. Thus, when treating depression with antidepressive drugs it is important to take into account the possible influence on weight and to choose a drug that does not cause weight gain.
One major limitation in the present study was that self-report questionnaires, such as HSCL-25, give very limited data on lifetime depression. It gives information on depressive symptoms at one time point. Depressive symptoms may be predictive of major depression, but they are not the equivalent of physician-diagnosed depression. Unfortunately, the validity of self-reported body weight and height data at 14 years cannot be evaluated in this cohort. It is probable that obese subjects might have underreported their body weight. Because we used an internal definition based on percentiles in classifying overweight and obesity to provide sufficient numbers to the analyses, this underreporting probably does not cause classification bias. In addition, among subjects lost to follow-up, obesity was slightly more common than among participants. As both the more obese and the more depressed may be at risk of not attending surveys,51, 52 this may limit the generalization of our results to the whole population. Finally, we did not have information on depression at the age of 14 years; thus, we did not have the possibility to assess whether depression in adolescence predicts later depression or obesity.
The strength of this study is in its design: a large, population-based prospectively followed birth cohort. Secondly, depression could be measured in three different ways by using the HSCL-25 and the use of antidepressants as a measure of current depression and physician-diagnosed depression as a measure of lifetime depression. Thirdly, the HSCL-25 has proved to be an acceptable screening scale in obtaining information on symptoms of depression in normal populations and also in this database.26, 53
In conclusion, obesity in adolescence might be associated with later depression among female subjects, abdominal obesity among male subjects may be closely related to concomitant depression, and being overweight/obese both in adolescence and adulthood may be a risk for depression among female subjects. In clinical practice, it is important to take into account the growing rates of obesity among children and adolescents. Longitudinal studies are needed to explore the connection between obesity and depression.
About this article
Journal of Behavioral Medicine (2018)