Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers, 2015, Schmidt et al

An old paper, but it has a measure of salivary cortisol in healthy volunteers.

Abstract

Rationale
There is now compelling evidence for a link between enteric microbiota and brain function. The ingestion of probiotics modulates the processing of information that is strongly linked to anxiety and depression, and influences the neuroendocrine stress response. We have recently demonstrated that prebiotics (soluble fibres that augment the growth of indigenous microbiota) have significant neurobiological effects in rats, but their action in humans has not been reported.

Objectives
The present study explored the effects of two prebiotics on the secretion of the stress hormone, cortisol and emotional processing in healthy volunteers.

Methods
Forty-five healthy volunteers received one of two prebiotics (fructooligosaccharides, FOS, or Bimuno®-galactooligosaccharides, B-GOS) or a placebo (maltodextrin) daily for 3 weeks. The salivary cortisol awakening response was sampled before and after prebiotic/placebo administration. On the final day of treatment, participants completed a computerised task battery assessing the processing of emotionally salient information.

Results
The salivary cortisol awakening response was significantly lower after B-GOS intake compared with placebo. Participants also showed decreased attentional vigilance to negative versus positive information in a dot-probe task after B-GOS compared to placebo intake. No effects were found after the administration of FOS.

Conclusion
The suppression of the neuroendocrine stress response and the increase in the processing of positive versus negative attentional vigilance in subjects supplemented with B-GOS are consistent with previous findings of endocrine and anxiolytic effects of microbiota proliferation. Further studies are therefore needed to test the utility of B-GOS supplementation in the treatment of stress-related disorders.

 

So, these researchers with links to the Department of Psychiatry at the University of Oxford have BPS leanings and mention HPA axis dysfunction in the article. They wanted to find out if prebiotics could help lower morning cortisol.

Three areas - placebo, and two sorts of prebiotic, all in healthy volunteers. The sample sizes are very small, so I don't think we can take too much away on whether prebiotics really lower cortisol. But, what I wanted to show you were the cortisol results for healthy people, and this group getting excited about lowering cortisol levels.



The x axis is the sampling times, upon waking and then every 15 minutes for an hour. First off, look at the variation over that hour.

Second, there is a bit of variation between the groups, even just pre-supplement.

Here's some of the discussion where the authors seem really happy with seeming to have lowered the cortisol levels:

So, we have BPS-leaning researchers, very happy that dosing with a prebiotic found in vegetables and dairy products might be reducing peak salivary cortisol by more than third.

 

If that chart on the left is of cortisol measured at various times, it could be that the waking cortisol peak is delayed. That might be normal if the usual waking time is later than people who have to get to the office, especially if the testing was done at home.

If DHEA is normal , and the DHEA/cortisol ratio is normal, then cortisol levels must also be fairly normal.

 

Here's another cortisol paper that I find interesting:

Day-to-Day Differences in Cortisol Levels and Molar Cortisol-to-DHEA Ratios among Working Individuals
Kim et al 2010

Abstract
Purpose
The present study was carried out to determine day-to-day differences in cortisol levels and the molar cortisol-to-dehydroepiandrosterone (DHEA) ratio (molar C/D ratio) in working subjects.

Materials and Methods
The cortisol and DHEA levels were measured from saliva samples collected 30 minutes after awakening for 7 consecutive days in full-time working subjects that worked Monday through Saturday. To determine the day-to-day differences within subjects, the collected data was analyzed using variance (ANOVA) for a randomized complete block design (RCBD).

Results
The cortisol levels from samples collected 30 minutes after awakening on workdays were similar to each other, but were significantly different from the cortisol levels on Sunday. The DHEA levels were not significantly different between the days of week. The DHEA levels on Monday and Tuesday were relatively lower than the levels on the other weekdays. The DHEA levels on Thursday and Friday were relatively higher than the other days. The molar C/D ratios on Sunday were significantly lower than those on workdays. The molar C/D ratios on Monday and Tuesday were significantly higher than those on Wednesday or other workdays.

Conclusion
The cortisol levels and the molar C/D ratios demonstrate differences in adrenocortical activities between workdays and non-workdays, but the molar C/D ratio additionally represents differences in adrenocortical status between the first two workdays and other workdays. Thus, it is possible that the day-to-day differences in the cortisol levels and the molar C/D ratio represent the adrenal response to upcoming work-related stress.



These people in Korea worked from Monday to Saturday, and had Sunday off. Cortisol and DHEA were measured 30 minutes after waking.
The mean cortisol levels on Monday through Saturday were in the range of 13.67-14.94 nmol/L, and those on Sunday were 10.39 nmol/L. That's a pretty big difference - just because of the day.

There isn't a chart of cortisol levels, but there is one of the cortisol/DHEA ratio. Given that DHEA levels were pretty constant, we can look at the chart as essentially just showing cortisol differences. Look how people had higher cortisol on wakening early in the week, lower values later in the week, and substantially lower cortisol on Sunday, the day they had off. Sampling was done 30 minutes after waking.




Also, look at the variation on any single day - the bars shows it was considerable. Healthy people can have quite different cortisol levels in any single measure.

This (and various other papers like the one that showed how quickly rowers increased their cortisol levels just by training more) suggests that there can be lots of reasons for variation in cortisol, and a number of reasons why people with ME/CFS and Long Covid (who don't routinely have to leap out of bed and run for the bus, and don't tend to be training to run a half marathon) might have levels a bit lower than average, but still with a healthy range.

If anyone wants to prove that cortisol levels actually mean something in ME/CFS, then they need to get some people with similar sleep and activity schedules (and perhaps even a similar attention to eating a good fibre-filled diet) to be controls, to make comparisons with.

 

I'm rather puzzled as to why so many researchers seem to think increasing cortisol in people with ME/CFS and Long Covid is desirable, when most of them have perfectly good levels for their level of activity already.