# Night shifts, caffeine and crashes: what to track first

Caffeine timing, sleep opportunity and symptom patterns are more informative than treating a crash as proof of abnormal cortisol.

Canonical: https://velri.co/blog/night-shift-caffeine-cortisol-before-nad-marisol
Publisher: Velri (https://velri.co/about)
Published: 2026-06-22
Updated: 2026-09-30
Editorial policy: https://velri.co/editorial-policy

When caffeine no longer seems to carry you through a night shift, start with the pattern: how much you use, when you use it, when you sleep and what “crashing” feels like. Caffeine sensitivity and the speed at which people clear it vary, and too much can contribute to sleep problems or other symptoms. [1]

The sleep and caffeine record is the starting point for investigating the fatigue.

## Count sources, not just cups

Coffee strength and serving sizes vary. Caffeine can also appear in tea, energy drinks, supplements, bars and some nonprescription medicines. The FDA recommends considering all sources when assessing intake. [1]

A useful record includes the product, approximate amount and time. “Three coffees” is less informative than knowing whether they were small servings early in the shift or large drinks close to the planned sleep period.

## Put sleep beside the caffeine record

NHLBI recommends a sleep diary that includes sleep and wake times, naps, daytime sleepiness, caffeine, alcohol and exercise when investigating insomnia. For shift work, days off are part of that picture too. [2]

The record may reveal too little opportunity to sleep, frequent interruptions or a schedule that changes repeatedly. Those are distinct concerns, even when they all lead to feeling exhausted. [2][3]

## What can cortisol testing tell you?

Cortisol testing is used to investigate specific disorders of excess or deficiency. Levels change during the day, and stress, exercise and medicines can affect results. One measurement does not diagnose the reason for persistent fatigue. [4]

The Endocrine Society also states that “adrenal fatigue” is not a scientifically established condition and that tests marketed to diagnose it are unsupported. [5]

## Where does NAD+ fit?

NAD+ biology does not establish that a treatment will correct fatigue caused by this schedule. Reviews describe unresolved questions about translating NAD+ research into safe human benefits. [6]

A timeline of caffeine, sleep and symptoms makes the fatigue easier to investigate.

## Sources
[1] Spilling the Beans: How Much Caffeine is Too Much? | FDA (2024). https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
[2] Insomnia - Diagnosis | NHLBI, NIH (2022). https://www.nhlbi.nih.gov/health/insomnia/diagnosis
[3] Module 2. Sleep is a Basic Need | NIOSH | CDC (2020). https://www.cdc.gov/niosh/work-hour-training-for-nurses/longhours/mod2/03.html
[4] Cortisol Test: MedlinePlus Medical Test (2024). https://medlineplus.gov/lab-tests/cortisol-test/
[5] Adrenal Fatigue | Endocrine Society (2022). https://www.endocrine.org/patient-engagement/endocrine-library/adrenal-fatigue
[6] NAD+ metabolism and its roles in cellular processes during ageing (2021). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7963035/

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