A new study from Homones and Behavior reveals a black-white difference among children in cortisol levels throughout the day. A flatter diurnal slope is associated with more chronic stress and health problems.
As shown in the graph, whites wake up with a significantly higher level which then falls more quickly throughout the day. The different slope remains even when the following factors are controlled: age, gender, non-steroid medication usage, sleep, wake time, socioeconomic risk, psychosocial risk, perceived discrimination, harsh parenting, and parental monitoring.
Compared to blacks, the slope for Hispanics is more similar to whites, although Hispanics do have lower cortisol levels than whites by evening time.
The authors suggest that since morning levels of cortisol are known to be influenced by genes, the racial difference might be due, in part, to genetic differences.
My first full paper included diurnal measurement of cortisol (plus a dexamethasone suppression test) - compared depressed and controls
ReplyDeletehttp://bjp.rcpsych.org/content/150/6/791.short
But 25 years down the line, I am still not sure what it means.
I think if 'depressed' people have low cortisol, then they probably suffer more from fatigue, aches and pains - since cortisol is an anti-inflammatory and analgesic.
I suppose, though, as a general point, that significance testing is potentially misleading in the case of comparing traits between racially distinct populations which have been separated for scores of generations.
There isn't any particular reason to assume that they would have identical hypothalamo-pituitary-adrenal axis activity - so the null hypothesis of 'no difference' does not necessarily apply - which perhaps means that measured differences are even more likely to be non-random than the significance level suggests. But I don't have any idea what it means.