Abstract
BackgroundMost studies on cortisol have focused on smaller, selected samples. We therefore aimed to sex-specifically study the diurnal cortisol pattern and explore its association with abdominal obesity in a large unselected population.MethodsIn 2001–2004, 1811 men and women (30–75 years) were randomly selected from the Vara population, south-western Sweden (81% participation rate). Of these, 1671 subjects with full information on basal morning and evening salivary cortisol and anthropometric measurements were included in this cross-sectional study. Differences between groups were examined by general linear model and by logistic and linear regression analyses.ResultsMorning and Δ-cortisol (morning – evening cortisol) were significantly higher in women than men. In both genders older age was significantly associated with higher levels of all cortisol measures, however, most consistently with evening cortisol. In women only, age-adjusted means of WHR were significantly lower in the highest compared to the lowest quartile of morning cortisol (p = 0.036) and Δ-cortisol (p < 0.001), respectively. Furthermore, when comparing WHR above and below the mean, the age-adjusted OR in women for the lowest quartile of cortisol compared to the highest was 1.5 (1.0–2.2, p = 0.058) for morning cortisol and 1.9 (1.3–2.8) for Δ-cortisol. All findings for Δ-cortisol remained after adjustments for multiple covariates and were also seen in a linear regression analysis (p = 0.003).ConclusionIn summary, our findings of generally higher cortisol levels in women than men of all ages are novel and the stronger results seen for Δ-cortisol as opposed to morning cortisol in the association with WHR emphasise the need of studying cortisol variation intra-individually. To our knowledge, the associations in this study have never before been investigated in such a large population sample of both men and women. Our results therefore offer important knowledge on the descriptive characteristics of cortisol in relation to age and gender, and on the impact that associations previously seen between cortisol and abdominal obesity in smaller, selected samples have on a population level.
Highlights
Most studies on cortisol have focused on smaller, selected samples
The vast majority of previous studies of cortisol have focused on smaller selected groups. While these studies offer important contributions for understanding the underlying mechanisms of cortisol metabolism and its association with e.g. abdominal obesity, larger studies are needed to add information on what impact associations on smaller selected samples have on a population level
Basal salivary cortisol Age-differences In both men and women evening cortisol was significantly higher in older subjects compared to younger, while the same pattern for morning cortisol was seen in men only (Table 2)
Summary
Most studies on cortisol have focused on smaller, selected samples. We aimed to sex- study the diurnal cortisol pattern and explore its association with abdominal obesity in a large unselected population. Cortisol is secreted in a specific diurnal pattern with a normal curve presenting a sharp peak in the early morning to gradually decrease over the day and end up very low in the evening and at night. Except for the increased secretion in stressful situations, there are smaller peaks during the day when the body is exposed to exercise, food, and tobacco [1]. Aging is hypothesised to alter the function of the HPA-axis in both men and women with increasing cortisol levels as a result, especially regarding nocturnal levels [2,3,4,5,6,7]. Previous studies have indicated that cortisol levels differ between men and women [2,3,4,5,8,9]. While several of the studies have found men to have higher levels than women there are inconsistencies regarding in what age-groups these findings have been seen [2,3,4,5]
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