Why Morning Cortisol, Collection Time are so Important?

Why Morning Cortisol, Collection Time are so Important?

Anil Kumar, PhD
Created On
Aug 03 2020
Last Updated
Dec 05 2021

Cortisol levels change throughout the day. But they change a lot within first hour of waking up.

This dramatic rise and subsequent drop in the morning is called Cortisol Awakening Response (CAR).

It is a relatively new finding, when Jens Pruessner and Clemens Kirschbaum first systematically reported this trend in 1997.


Source:The daily or diurnal trend of cortisol stress hormone.

The Diurnal Cortisol Trend

To capture the cortisol variation during the day, a 4-point diurnal cortisol test tries to measure the changing cortisol levels through out the day. This involves collection of four samples during the day.

The first sample collection is right after waking up. Due to economical reasons, it is difficult to collect multiple samples early in the morning.

Therefore, it is extremely important to ensure proper protocol is followed in collection for best results. It helps to know the trend of morning cortisol variation and the factors affecting it.

Factors affecting morning cortisol levels

The early morning cortisol is affected by several factors:

  • The exact time of collection after waking up—levels during first 15 minutes are flat but they rapidly change in next 30 to 60 minutes.
  • Darkness or dim light or full exposure to sunlight when waking up—the peak levels further rise with more light.
  • Season of the year—which again correlates to the amount of light.

Source: The effect of season, daylight saving and time of sunrise on cortisol.

Although day of the week, including weekends, have no appreciable impact in morning levels, amount of light and other motivational factors might complicate collection time.

Therefore waking hours between weekday and weekends should be carefully monitored.

Collection of morning samples should be temporarily avoided or further delayed during the following conditions:

  • Current illness—e.g., flu, fever, common cold can affect measurement, which should be postponed until full recovery (Adam and Kumari, 2009).
  • Estimated ovulation—collection during this time should be postponed (around two days before and after) (Wolfram, 2011).
  • Jet lag—can have an effect up to 7 days (Doane., 2010).
  • Night time working hours can shift the diurnal cycle. This impact can be seen up to a week after change in working hours (Griefahn and Robens, 2010; Harris et al., 2010).

Other long term factors to consider

Several other factors are modulate morning cortisol levels and deserve careful consideration:

Most of these factors do not appreciably affect levels later in the day.


Difference in collection time.

Research shows inaccurate monitoring of morning cortisol collection time is more common that realized. The recorded time is often late, and can impact the results.

Careful monitoring of actual wake up time versus self-reported time showed 1 in 5 people actually woke up earlier than what they had reported. This could be anywhere between 5 mins to 30 mins. For 1 in 7 people, this gap was over 30 minutes.

However, any difference over 15 minutes can cause significant variation in results.

Difference of 5 to 10 minutes at the beginning, right after breaking the sleep is likely not critical, since the rise in cortisol levels few minutes after waking up is still small.

But anything after first 15 minutes starts to have an impact due to steep rise in the levels at this time.

Researchers have identified multiple reasons why people collect their morning samples later than expected:

  • Avoiding the discomfort of collection.
  • Might need to prioritize other responsibilities.
  • Sleep inertia, being half-asleep without being fully mentally awake and no body movement. That makes it difficult to identify exact time of waking up, despite well-intentioned efforts.

What can be done for accurate morning cortisol collection?

One simple way to motivate people is by clearly stating that collection time will objectively affect their results.

It also helps if they know their morning sample is one of the most important measurement, and accurate documentation of this particular sample is crucial. Having a normal routine is useful.

Other methods include:

  • Using a diary that logs time of waking up and collection. Keeping the kit next to bed, with a pen to note down the time has been found helpful.
  • Using an alarm to wake up—research shows the cortisol spike in morning is unaffected by whatever method is used to wake up.
  • Use of smart phone to track time—taking a picture at collection will add a time stamp to validate the time later on. However, the waking up time still needs to be monitored.
  • Heart beat monitors—when tied to the chest they can accurately provide waking up time. Heart beat increases once you are awake.
  • Other techniques include sample collection in a sleep lab, automated blood collection, wrist actigraphy, or polysomnography—however, all these methods are either expensive or do not represent natural setting.

Concrete steps for morning sample collection.

Although, how you wake up seems to have no impact on the results (Stalder, 2009; Wüst, 2000b), what you do next is important:

  1. What it means to be awake: When you are awake, i.e., you are conscious: you know who and where you are; you are in a state that is clearly different from when you were sleeping even though you may still feel tired.
  2. Avoiding premature awakening: If you wake during the middle of the night and plan to go back to sleep, do not begin sampling; please only begin when you are awake for the final time before you plan to get up for the day.
  3. Refraining from dozing off: During this measurement, please do not fall back to sleep or ‘doze’ after your initial awakening. You can stay in bed or get out of bed but please stay awake (even if you are not fully alert) during and after the saliva sampling period.

How to reduce errors in morning cortisol results?

Except water, drinking or eating anything might affect the results. Here are few recommendation:

Things to Avoid:

It is Okay:

To lie down or moving around for normal activities doesn’t show any impact (Hucklebridge, 2002; Wilhelm, 2007).


Brushing teeth, is not known to have any significant effect on morning cortisol levels (Gröschl, 2001). However, vigorous brushing–that might result in bleeding–the impact of this blood in the saliva is not so clear (Kivlighan, 2004).

What factors are not clearly defined for morning cortisol levels?

  • The duration and quality of sleep—impact is unclear but recommendation is to follow normal routine.
  • Mental health—there is some data indicating morning levels may have influence of events from previous days, especially any negative experiences (of loneliness, threat, lack of control, etc.). Steep rise in morning levels might be expected when a challenging and demanding day ahead is expected (Adam, 2006; Fries, 2009; Wilhelm, 2007). In that sense, morning levels are an indication of the day ahead.

Although labs accept samples up to several weeks, for best results, one should immediately mail the saliva samples to the lab. In case of delay, store them in the refrigerator until ready to ship.

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