In this Icelandic cohort we investigated the impact of the Great Depression on size at birth and adult obesity, impaired fasting glucose, and dyslipidemia in 2750 Icelanders living in Reykjavik. We found that infants with birth year exposure to the Depression were of lower birth weight. In adulthood, Depression-born females had a higher mean BMI and greater odds of being obese but this effect was not observed in males.
With regards to size at birth, there was a significant decline in birth weight and ponderal index from 1925 to 1934 indicative of infants being born thinner as the economic impact of Depression progressed. Although birth weight still remained relatively high, the decreasing ponderal index is suggestive of increasing fetal undernutrition along with economic and environmental influences as there is a distinct and consistent drop after the initial onset of the Depression in Iceland in 1930.
The 1920s and 1930s in Iceland were characterized by increased migration into Reykjavik and changes in birth weight may also be a consequence of overcrowding which can negatively affect birth size 
. The current cohort includes only city residents and may capture some of this early migratory trend into Reykjavik. The flux in birth weight may be reflective of the shifting urban population however, as all participants were born and living in Reykjavik when recruited into the study, it is unlikely that this had a substantial influence on the outcomes measured.
In addition to birth size, studies have suggested accelerated postnatal growth in thin infants may contribute to later disease 
. Between the ages 8 to 13 years, both Depression-born boys and girls were taller and heavier than their counterparts born prior to the Depression, despite having a similar BMI at age 8. As the children grew older, those with birth year exposure to the Depression had faster BMI gain which may have placed them at greater risk of developing obesity in adulthood.
It should be noted that the environment during which these participants were growing was quite different. Children born between 1925 and 1929 were growing-up during the Depression where access to food was more difficult and costly 
, while those born during the Depression (1930–1934) were on average growing in a more plentiful environment. Historically, this was primarily due to improvements in the fortunes of the Icelandic economy during the Second World War. Iceland experienced higher economic growth than most European countries from increased exports and greater demand created by the British and later American occupation forces in the country. The simultaneous economic change was likely linked with increased efforts by parents of Depression-born children to encourage weight gain. The relative contribution of an adverse prenatal environment during the Depression coupled with an improved situation may have contributed to the differences in childhood growth patterns.
In adulthood, we observed higher fasting glucose levels and increased obesity only among women with birth year exposure to the Depression. We observed virtually no difference in BMI or odds of obesity among men. There is evidence that increasing glucose intolerance and obesity can coincide with transition to an environment of better nutrition 
. However, both sexes experienced comparable environmental exposures suggesting the gender differences did not arise from the same etiologies. Previous analysis in this cohort also found sex-specific differences, with stronger inverse associations between birth weight and truncal fat 
and glucose intolerance 
among women at adult age. Similar findings were published on the Hertfordshire cohort, where fasting glucose measures were more strongly inversely associated with birth weight in women 
We did not find the odds of impaired fasting glucose or dyslipidemia for either sex to be linked to birth year exposure to the Depression. The relatively high birth weight in Icelandic infants has been proposed to have a protective effect with respect to diseases (i.e. coronary heart disease, hypertension) related to small size at birth 
. In several epidemiological studies higher birth weight was associated with increased lean body mass but not adiposity later in life 
. The difference in birth weight between infants born prior to versus during the Depression may reflect a lower proportion of lean body mass in the Depression-born infants. As muscle is an important site for glucose homeostasis, this could lead to abnormalities in blood glucose 
which may explain the slightly higher fasting glucose levels we observed in adult women.
While the findings of greater cardiometabolic risk factors primarily among women corroborate those from other epidemiological cohorts 
, there are several possible limitations. Data on maternal birth or adult size, gestational age or placental function was not available for analysis and their effect on birth size in this cohort is unknown. However, adjustments for strong predictors of birth weight (i.e. maternal age and parity) performed in this current study did not affect the outcomes.
Although the participants were recruited at various ages (33–65 years), our findings do not appear to be influenced by a recruitment effect. In addition, Vilbergsson et al 
previously reported that prevalence of non-insulin dependent diabetes in this cohort was consistent between the recruitment years 1967–1991. Thus, with regards to impaired fasting glucose this allows for a fair comparison between the subjects based on calendar year exposure to the Great Depression. The relationship between birth size and adult hypertension has been previously discussed in this cohort 
. We observed minor decreases in systolic and diastolic blood pressure which coincided with increasing use of anti-hypertensive medication for those recruited later in the cohort. Adjusting for this trend would not be possible without adjusting for calendar year therefore blood pressure was not included in this current analysis.
This cohort represents a population that was undergoing both economic and environmental changes during development in utero and early childhood 
. The individual impact of the Depression cannot be fully quantified, yet on a cohort level the distinct increase in infants with low ponderal index suggests the environmental strain was considerable enough to affect maternal health condition and birth size of offspring. Ultimate height and weight is a result of the interaction between many factors, but it appears that even restricted but non-famine like conditions experienced in utero (based on birth year) can modestly influence risk of later obesity while other cardiometablic risk factors (i.e. triglycerides, cholesterol, and glucose levels) seem to be less sensitive to these conditions. We also found that women were more susceptible to these conditions, which is in line with previous findings from this cohort.